American Journal of Plant Sciences, 2013, 4, 2092-2111
Published Online November 2013 (
Open Access AJPS
Morphological Diversity of Populations of the Genus
Prosopis in the Semiarid Chaco of Northern Cordoba and
Southern Santiago Del Estero
Marisa Jacqueline Joseau1*, Aníbal Ramón Verga2, María del Pilar Díaz3, Norma Beatríz Julio4
1Department of Forestry, Faculty of Agricultural Science, National University of Cordoba (UNC), Córdoba, Argentina; 2Institute of
Physiology and Plant Genetic Resources (IFRGV), Agricultural Research Center (CIAP), National Institute of Agricultural
Technology (INTA), Córdoba, Argentina; 3Statistics and Biostatistics. School of Nutrition, Faculty of Medical Sciences, UNC,
Córdoba, Argentina; 4Population Genetics and Evolution, Faculty of Exact, Physical and Natural Sciences, UNC, Córdoba, Argen-
Email: *
Received January 13th, 2013; revised February 13th, 2013; accepted March 15th, 2013
Copyright © 2013 Marisa Jacqueline Joseau et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The objective of this study consisted in the characterization of morphological variability presented in the Prosopis
population in the corridor that unites the semiarid with the arid region in Argentina. In this region, four species of Pro-
sopis get in contact (P. chilensis, P. flexuosa, P. alba and P. nigra). Due to the fact that these species make fertile hybrids,
this corridor has an enormous diversity. The mother’s allowed the differentiation of five morphologic groups, which
from the point of view of classic taxonomy have been classified in 16 taxa. Only groups 3 and 4 presented intermediate
characteristics. The morphologic study of the descendants showed that the regrouping of the intermediate groups had a
high error rate. This fact reaffirms the condition of intermediate groups. The canonical correlation analysis between the
morphologic variables of the mothers and the seedlings revealed that each morphologic group had its own association of
canonical variables between mothers and their seedlings, and that the variability observed in the set of the mothers and
their seedlings follows a certain order. The enormous existing morphologic diversity in the Prosopis populations of the
semi-arid Chaco of the north of Córdoba and southeast of Santiago del Estero was ordered in five morphologic groups.
The descendant’s morphologic studies confirmed the existence of the defined morphologic-genetic groups.
Keywords: Algarrobo; Morphological Groups; Hybrid Swarm; Semi-Arid and Arid Chaco
1. Introduction
Widespread deforestation and declining condition of the
global forest resulted in an environmentally, economi-
cally and aesthetically impoverished landscape [1]. Ar-
gentina is no exception as it has lost 70% of its native
forests over the last 114 years [2].
The change in forest cover, its quality and composition
have influenced the size and nature of genetic variation
in forest trees [3]. Some tree species of the genus Pro-
sopis are of great economic and ecological interest
among the trees in Argentina. Only relict of the once
wide forest of Prosopis remain and the irrational exploi-
tation generates genetic impoverishment, with alarming
loss of biodiversity [4].
The genus Prosopis Linnaeus emend. Burkart is within
the family Fabaceae (Leguminosae), subfamily Mimo-
soideae [5]. Based on differences in floral and vegetative
features, Burkart [6] defined the generic limits and di-
vided the genus into five sections and within the Algaro-
bia section identified 5 separate series according to the
type of vegetative growth. While the generic limits and
the division into sections are generally accepted, there
are debates as to the range in terms of species as Burkart
defined [6]. Being the most recent and complete taxo-
nomical classification of the genus [5], this is taken as
the basis in this work. Thus the species studied in this
research belong to Algarobia section Chilenses series.
In Burkart classification [6], 44 species and 27 varie-
ties of Prosopis are listed. The existence of populations
of Prosopis with distinct characteristics led Burkart to
*Corresponding author.
Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero 2093
describe many as separate species or varieties, even
though several are known to hybridise [5]. Of the five
sections distributed in arid and semiarid regions of Africa,
America and West Asia, three are present in the Argen-
tine territory: the Strombocarpa, Monilicarpa and Al-
garobia sections with a total 27 species; 21 of them be-
long to Algarobia section [7].
The close semiarid region located between the foot-
hills of the Sierras de Córdoba and those of Sumampa in
Santiago del Estero and Salinas Grandes, in both prov-
inces forms a narrow corridor linking the semiarid Chaco
with the arid Chaco. In this corridor, species typical of
semiarid Chaco Prosopis described as Prosopis alba and
P. nigra penetrate from the North, while P. flexuosa, P.
chilensis, species dominant in arid Chaco penetrate from
the South. In this region individuals of intermediate
morphology that could correspond to interspecific hy-
brids are observed and constitute part of hybrid swarm
among these four species.
Thus, this area clearly defined by geographical fea-
tures (mountains and saltworks) would be one of the
main centres of diversity (if not the most important) of
genus Prosopis in Argentina
There are hybrid swarms in many groups of plants. In
woody plants this has been described in the genus Juni-
perus, Quercus, Aesculus, Eucalyptus y Opuntia [8] and
more recently in the genus Prosopis [9-13]. The taxon-
omy of the genus is quite problematic [10]. The problems
of the limitation of species in this genus are found mostly
in Algarobia Section. Apparently the clear absence of
reproductive isolation barriers between species [9,14-17]
and the sympatry [6,18,19] facilitated the hybridization
and introgression and contributed to the observed mor-
phological and genetic variability in populations [19,20].
Species linked by frequent or occasional hybridization
are a singameon. This was defined by Grant [8] as a
group of species that hybridize and act as a biological
species, reproductively isolated from other similar groups.
Given the ability of some species hybridization of Sec-
tion Algarobia (P. alba, P. nigra, P. chilensis y P. flexu-
osa) some authors [9,21,22] suggested that they consti-
tute a singameon, which makes it difficult to identify
them in the field.
Previous studies in Section Algarobia, chroma-
tographics [9,14,23,24], seminal protein electrophoresis
[25,26] and isoenzyme electrophoresis [11,21,27-30]
indicated a low degree of differentiation between species,
which could be explained by frequent hybridization be-
tween them in an area of sympatry, favored by weak iso-
lation barriers and environmental modifications [4].
However, morphological taxonomic studies indicate a
strong differentiation between the different species
This apparent contradiction is generated because there
are individuals who truly represent the species listed,
which are even clearly different, both morphologically
and ecologically. When studying individuals in regions
where species come into contact, a large number of in-
termediate individuals sprang up that cannot be clearly
classified in any of the species. This leads to the conclu-
sion that the result will depend on the used criterion for
selecting individuals that will represent the species in
question. If one includes only those who strictly respond
to the characteristics of the pure species, differentiation
between them will be important and the intraspecific
variation genetic and morphological will be minor. As
more individuals intermediate are added, responding in
part to the characteristics of the species, this becomes
unclear with respect to the other species, decreasing in
differentiation and increasing in diversity [12].
The hybridization of the environment that occurs due
to human activity such as road construction, agriculture,
irrigation and forestry [8,9,31] is one of the conditions
that encourage the establishment of hybrids [8,9].
The “algarrobos” present in the contact area of Pro-
sopis chilensis-P. flexuosa-P. alba-P. nigra in the semi-
arid Chaco of the North of Cordoba and the South of
Santiago del Estero are apparently shown as a continuum
from the morphological point of view. In many cases it is
impossible to classify a particular individual in any of the
species mentioned, because their morphological charac-
ters correspond to more than one species simultaneously,
making it almost impossible for his taxonomic classifica-
However it is possible that, within this apparent con-
tinuum, there are groups of individuals that resemble
closer among themselves and are away from the pure
species mentioned, constituting genetic units with adap-
tation to specific niches appearing in these environments
Identifying the groups that these individuals can form
from the point of view of morphological characters
(“morphological groups defined”) will serve as a starting
point to select genetic units of the hybrid swarm, which
retain their adaptive traits and productivity in their off-
spring and become so in the basis for the improvement
and use of these genetic resources.
Hybrid areas constitute a reservoir of variation of im-
portance to conservation and may be used as base mate-
rial for breeding programmes in the long term while the
areas of “pure species”, though presented less variation,
surely have greater stability and adaptation to “normal”
conditions, being able to provide base material for use in
the short term [12,32].
The availability of appropriate genetic material, to-
gether with a better understanding of intraspecific varia-
tion in tree species, is a requirement for the development
and domestication of these species [33,34]. The aim was
Open Access AJPS
Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero
Open Access AJPS
to characterize the morphological variation existing in
populations of Prosopis in the Semiarid Chaco of north-
ern Córdoba and southern Santiago del Estero.
contact area Prosopis chilensis-P. flexuosa-P. alba-P.
nigra), following the direction of the corridor (north-
east-southwest). In addition to these gradients, there were
spatial discontinuities in the apparition of species of the
genus or start of the others not included in this study.
Thus, four samples were defined: Jume-Los Telares (Z1)
was defined to the town of Los Telares since moving
further North individuals of P. ruscifolia, a species
completely different from the morphological point of
view began to be seen (Table 1 and Figures 1(a) and (b)).
2. Materials and Methods
The materials for this research were seed and branches of
Prosopis chilensis, P. alba, P. flexuosa, P. nigra and
intermediate individuals, possible hybrids among these
four species in the Semiarid Chaco of northern Córdoba
and southern of Santiago del Estero.
The second was located near the Salinas Grandes: San
José de Las Salinas-Lucio V. Mansilla (Z2), the third
zone was established in an ecotone between two bio-
geographic subregions: Quilino-Huascha (Z3) and the
fourth was the most southern point of the corridor where
trees of Prosopis with pods were: Cruz del Eje-Tuclame
(Z4) (Table 1 and Figures 1(a) and (b)).
2.1. Exploration
In the late 1999 and early 2000 four areas (populations)
were identified based on the gradients of temperature and
precipitation in the Chaco Semiarid, in northern of Cór-
doba and southern of Santiago del Estero to get the study
material (Prosopis individuals most characteristic in the
Table 1. Quantity and location of harvested trees.
Zone Latitude Longitude Altitude (msnm) A (mm)B (˚C)
The hottestThe coldest Individuals total per zone
Z1 28˚59' - 29˚23' 63˚26' - 63˚41' 108 - 480 597 - 60026.9 11.5 27
Z2 29˚47' - 30˚08' 63˚42' - 64˚31' 191 - 193 394 - 45327.7 12.5 15
Z3 30˚12' - 30˚36' 64˚24' - 64˚46' 393 - 689 445 - 56026.2 10.8 23
Z4 29˚38' - 30˚45' 64˚38' - 65˚14' 275 - 600 379 - 48127.6 11.5 20
Source: [43]. A = Average annual rainfall; B = Average monthly temperature.
Figure 1. Location: (a) Chaco Phytogeographic Province [37] and (b) Study area.
Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero 2095
2.2. Samples
This study sought to achieve order and classification of
the genus Prosopis species found in the region, whose
morphological variability appears in first as a continuum,
in biological separated units to make handling possible.
Four areas were selected located at different lattitudes
with different environmental characteristics and usage,
representing the different conditions that occur in this
geographical corridor. In each area or population sought
to capture the great variability of possible shapes unbi-
ased manner, providing that individuals submit pods ma-
ture and intact from the morphological viewpoint. It is
worth mentioning that individuals with faulty leaflets
resulting from the use of herbicide application in nearby
fields were not harvested.
2.3. Harvest
Table 1 shows the number of individuals harvested
according to zones. The total amount of trees harvest was
85. Located at each harvested individual by geographic
positioning (GPS). Measurements considering height,
stem diameter and canopy, were classified by age group
and health status, following the methodology and harvest
forms of National Germplasm Bank of Prosopis (BNGP)
of FCA-UNC [35]. A harvested tree was assigned a
number from 1 to 85 (Table 2) and at harvest time the
species it belongs to was not specified.
The fruits threshed and seeds obtained after being
dried were placed in a freezer for ten days to bruchid
control [36], later stored at 4˚C in sealed jars retaining
their identification.
From each accession fruits and two branches with ma-
ture leaves were taken off, material to herbaria, to do
morphological studies under two different classifications:
classical classification and numerical taxonomy. So, the
85 herbaria samples collected were sent to the Labora-
tory of Vascular Plants of the Buenos Aires National
University for identification based on pre-established
taxonomic criteria for the differentiation of pure species.
As a result of this classification 16 taxa were obtained
(Table 2). Notably, in this identification, any pure spe-
cies of Prosopis flexuosa were present in the sample.
On the other hand morphological analysis was carried
out based on numerical taxonomy whose methodology is
detailed below. To order mother plants taxonomically,
morphological analysis was conducted and, based on the
obtained clustering; later analysis on the progeny was
The zones are located in the Chaco Phytogeographic
Province (Gran Chaco) [37-40]; more exactly in the
Semiarid Chaco Subregion [37,38].
The main pocket is constituted by a geographical cor-
ridor whose boundaries both Cordoba and Santiago del
Estero are Salinas Grandes towards the West and the Sier-
ras towards the North and East. This pocket is limited
Table 2. Identification of mother plants through classical taxonomy.
Species Symbol Number of the parent plant Total individuals
P. alba Pa 11-12-18-20-26-84 6
P. alba (folíolos algo menores) Pafm 23 1
P. alba x* Pax? 2-31-39-52 4
P. alba x P. nigra Paxn 22 1
P. alba ó P. chilensis x P. flexuosa. Paxf 41 1
P. chilensis x P . alba Pcxa 1-4-5-8-24-36 6
P. chilensis Pc 19-35-37-43-44-46-50-51-55-56-59-60-61-62-63-64-65-66-69-70-74-77-79-80-82 25
P. chilensis (folíolos algo menores) Pcfm 10-17-32-33-38-42-45-57-78 9
P. chilensis x* Pcx? 27-40 2
P. chilensis x P. flexuosa Pcxf 81-83 2
P. chilensis x P . flexuosa o P. nigra Pcxfon 68-75-76 3
P. chilensis x P. ruscifolia Pcxr 21 1
P. ruscifolia Pr 25 1
P. flexuosa o P. flexuosa x P. alba Pf o Pfxa 3-6 2
P. flexuosa o P. nigra x P. chil ensis Pfxc 53 1
P. nigra Pn 7-9-13-14-15-16-28-30-34-48-49-54-58-67-71-72-73-85 18
Unidentified S/ident. 29-47 2
Total taxa 16 85
Reference: *unidentified for lack of reproductive material.
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Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero
in the Sierras de Cordoba by Sierras of La Higuerita, of
Orcosuni, of Sauce Puncu, San Pedro Norte and Am-
bargasta [41], while the latter and Sumampa chain are
found in Sanitago del Estero. All of these mountains
have a North-South direction [41,42].
Chains of Sumampa and Ambargasta in Santiago del
Estero are merely an extension of the Sierras de Córdoba.
Their length within the province of Santiago del Estero is
60 kilometres and the transverse extension of two strings
together is about 40 kilometres [42].
Desertification caused by the degradation of soil and
vegetation is rated moderate to severe depending on the
area [37].
These areas constitute what in this work are set to
study populations. At harvest time, the identification of
the specimens sample was established by a number.
From the consulted bibliography, of data recorded on the
form of National Bank of germplasm of Prosopis, using
the classical classification the following description of
each area is provided, which has no other purpose rather
than to describe the situation in which each region was at
the moment of sampling. The expansion of the agricul-
tural frontier in recent years due to the cultivation of soya
may have changed some features of each study popula-
2.3.1. Z1. El Jume-Los Telares (Santia g o Del Ester o)
This region is located in the phytogeographic region of
western Chaco. The altitude varies from 108 to 480 masl
and average annual rainfall is about 600 mm. This region
is partially disassembled (Table 1).
From the point view of classical taxonomy, the sample
in this area consisted of 11 taxa, including six which
were made up of pure species (P. alba, P. alba with mi-
nor leaflet, P. chilensis, P. chilensis with leaflet minor, P.
nigra and P.ruscifolia) and the rest (39%) were interme-
diate taxa (Figures 2 and 3).
If the age composition of the sample is observed, it
shows that the most frequent carobs were elderly P. alba
and young individuals of P. nigra. Among the intermedi-
ate taxa mature individuals were predominant, which
Figure 2. Relative fre quency distribution of the taxa present
in Z1 according to age.
would indicate that the hybridization process in this re-
gion would not be recent.
The presence of greater numbers of young individuals
of P. nigra would coincide with the views expressed by
various authors [42,44], in that it is an unpalatable spe-
cies and therefore it thrives in degraded forest areas.
It is important to notice that the intermediate taxon
classified as P. chilensis x P. alba presented three age
2.3.2. Z2. Lucio V. Mansilla-San Jose de Las Salinas
(Córdo ba)
This area is near the Salinas Grandes, the altitude is be-
tween 190 and 195 masl and average annual rainfall
ranges from 394 to 453 mm.
Taxa diversity in the sample was lower than in Z1. Out
of 6 taxa found, three belonged to pure species: P.
chilensis, P. chilen sis (leaflets somewhat smaller) and P.
nigra and the rest were mainly composed of hybrids
among white carobs (Figures 3 and 4(a)).
The age composition of the sample in this zone indi-
cates a predominance of adult individuals, and in this
case young trees relate only to intermediate individuals
and P. nigra (Figure 4(a)).
2.3.3. Z3. Quilino-Huascha (Córdoba)
In this area individuals belonging to 7 different taxa were
harvested. Three belonging to pure species: P. chilensis,
P. chilensis with leaflets somewhat smaller, P. nigra and
four intermediate individuals, classified by Engineer
Palacios as carob hybrids mainly between blacks and
whites (Figures 3 and 4(b)). The species most commonly
identified in three stages (young, adult and years) was P.
chilensis (Figure 4(b)).
As for the age composition there was a predominance
of adult and elderly, only young individuals in the case of
P. chilensis and P. nigra were observed.
2.3.4. Z4. Cruz Del Eje-Tuclame (Córdoba)
The area has been quite altered by human activity, as
there are various agricultural crops such as citrus, grapes
and olives.
Harvested Prosopis species were P. chilensis, P.
chilensis (with leaflets somewhat smaller) and P. nigra.
Found hybrids were made of P. chilensis with P. flexuosa
or P. nigra, in the adult stage or years. This area is the
one which presented fewer taxa (5) (Figures 3 and 4(c)).
The species that showed more often in the sample
were elderly individuals of P. chilensis and adults P. ni-
2.4. Morphological Analysis
The morphological analysis, using the principles of nu-
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Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero 2097
Figure 3. Participation percentage of each taxon in the sample by zone.
Figure 4. Distribution of relative frequencies of taxa according to age present in: (a) Z2, (b) Z3 and (c) Z4.
merical taxonomy, was carried out at the level of mother
plants harvested field and level of offspring of these plant
2.4.1. Mother Plants
The branches and fruit collected during the harvest were
herborized and a total of 19 morphological characters for
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Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero
each tree were analyzed.
2.4.2. Leaf Characters
10 leaves from two sampled branches were taken into
account providing the following characteristics (Figure
Length of petiole (LPEC), length of pinnae (LPIN),
length of leaflet (LFOL) and separation between leaflets
(SFOL): mm with digital caliper.
Number of pairs of pinnae (NPIN) and number of pairs
of leaflets for pinnae (NFOL): number.
Width of leaflet (AFOL): mm, magnifying glass
graduated in tenths of mm.
Calculation: the relationship length/width leaflets
(L/AFOL). A total of 10 leaves by harvested tree were
2.4.3. Fr uit Chara ct er s
Were recorded the following characters were obtained
from 10 fruits taken from each mother plant (Figure 5):
Length of fruit (LFR). A graduated cable was extended
on each fruit in order to measure the length in cm.
Width of fruit (AFR). It was measured in mm on the
middle region of the fruit using a digital caliper.
Thickness of fruit (EFR). It was measured in mm with
a digital caliper on a central knuckle that had a seed.
Number of knuckles (NART). The number of knuckles
per fruit was counted.
Reference: Sinuosity of the branch (SRAMA),
Spinosity (ESPINA), Length of petiole (LPEC). Length
of pinnae (LPIN). Length of leaflet (LFOL). Width of
leaflet (AFOL). Separation between leaflet (SFOL).
Length of fruit (LFR). Width of fruit (AFR). Thickness
of fruit (EFR). Edge of fruit: 4.- rosary form (BORDE: 4).
Fruit shape: 3: spiraled (FORMA).
For the following variables of fruit a qualitative scale
was established (classes) as used by Verga [11]:
Fruit colour, with classes (COLOR): 1) uniform yel-
low; 2) yellow background with purple spots (mainly
edges), 3) preponderates purple or black on yellow ap-
pears with a very blocked or smeared.
Edge of fruit, with classes (BORDE): 1) Straight, 2)
some chokes, 3) strangulated on all knuckles, 4) rosary
Fruit shape, with classes (FORMA): 1) straight, 2)
falcate, 3) spiraled.
The relationship between length/number of knuckles
(L/NART) and the width/thickness (A/EFR) were also
included as characteristics of the fruit.
Branch characters: classes were established to qualify
the character of a degree from lowest to highest intensity
(Figure 5).
Sinuosity of the branch, with classes (SRAM): 1)
straight, 2) winding, 3) very winding.
Spinosity, classes (ESPINA): 1) boneless, 2) spiny, 3)
very thorny.
Figure 5. Illustration of the characters of leaf, fruit and branch in the mother plants.
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Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
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2.4.4. The Offspring
For the morphological study of mother plants offsprings
a trial in the nursery of Facultad de Ciencias Agropec-
uarias in November 2000 was established. Seedlings
were produced by direct seeding (seed scarified and
soaked in water at room temperature for 10 hours), in
bottomless tube packages of 6 cm diameter ×20 cm long.
This trial served to address two different aspects: 1) re-
cord variables of growth and form on each seedling and 2)
the morphological analysis.
Thus, for each seedling the height at four seedling ages
was measured: 39 (ALT1), 55 (ALT2), 118 (ALT3) and
168 (ALT4) days after sowing. The main stem and the
degree of spinosad after 180 days of the seedling were
also recorded.
Three levels were established for the variable shape of
the main stem (TALLO): 1) straight, 2) winding and 3)
very winding and three for the degree of spinosity
(ESPINA): 1) boneless, 2) moderately thorny, 3) very
10 seedlings per family were chosen at random and a
well developed leaf was taken from each one to do the
morphological analysis.
The following characteristics resulted from measuring
with digital caliper: Number of pinnae (NPIN), Number
of pairs of leaflets for pinnae (NFOL); Length of leaflet
(LFOL), Length of pinnae (LPIN), Separation between
leaflet (SFOL), and calculated with the HOJAS pro-
gramme [45]: Length of leaflet (LFOL), Width of leaflet
(AFOL), ratio length/width leaflet (L/AFOL), falcate of
leaflet (FALCA), area of leaflet (ARFOL), ratio apex
with total (AP/TOT) and apex of leaflet (APICE).
2.5. Morphological Relationships between
Mother Plants and Offspring
The association between the morphological groups of
harvested trees and their descendents was studied using
cannonical correlation analysis (CCA) between the group
of morphological variables of mothers and the group of
variables to their descendents, verifying their statistical
significance. This analysis was conducted for each mor-
phological group.
2.6. Statistical Analysis
2.6.1. Morph o l ogi cal Analysi s
This analysis was done to determine the morphological
distances (dm,) [12,13] from morphological characters. To
calculate dm Taxon software [46] was used. The matrix
used for the calculation of morphological distances dm
was dimension 79 × 19 for the number of trees and mor-
phological characters respectively.
2.6.2. Cl uster Anal ysis
For the formation of the morphological groups in the
mother plants morphological distance dm was used and
they were grouped according to the UPGMA clustering
method. Cluster analysis on the program NTSYS [47]
was carried out in order to see if it met the same clusters
in the offspring. It was considered that each offspring
belonged to same group of the parent plant.
2.6.3. Of Mother Plants
Of the 85 harvested plants 6 trees had to be rejected
(Trees N˚: 18-25-27-28-47) for the morphological analy-
sis because of lack of sufficient material. So, 79 mother
plants were analyzed morphologically in order to assess
the value of the characters for the morphological differ-
entiation and the formation of the groups. The total dif-
ferentiation of the characters (
T) and R correlation coef-
ficients between the matrix of average morphological
distance between groups and each emerging one to each
character were calculated.
2.6.4. Of the Offspring
A completely randomized design with 6 replications of 5
plants × 78 mother plants was used.
2.6.5. Di s cr i minant Ana lysis
To identify the homogeneity of the morphological groups
formed in both mothers and in offspring, a quadratic dis-
criminant analysis was done. To select the variables the
Stepwise method [48] was used. The program used for
this analysis was the SAS [49].
2.6.6. Morphol o gical Relationship s be t ween Moth e rs
and Offspring Plants
Relationships between morphological variables of moth-
ers and offspring could be established by means of mul-
tivariate canonical correlation analysis (CCA) [50]. This
analysis is used to establish the linear relationship be-
tween two groups of metric variables, some independent
and others considered as dependents. That is, the CCA
addressed the association between two sets or groups of
variables, identifying and quantifying the association.
The program used for this analysis was the InfoStat [51].
3. Results
3.1. Morphological Analysis
3.1.1. Mother Plants
Figure 6 shows that at the level of 78% two groups dif-
ferentiated. From the tree 1 to 52, corresponding to the
group of “white” and from 3 to 85 representing the
Within each of these two groups, clearly sub-groups
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Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero
Figure 6. Dendrogram obtained by UPGMA method based on morphological distance between individuals represented by all
the morphological characters of the mother plants.
were formed, which in some cases may correspond to
differences among species or the presence of intermedi-
ate individuals. At level of 70% the formation of 5
groups is observed (Figure 6).
Comparing these groups with the determinations made
in the Laboratory of Vascular Plants of the University of
Buenos Aires following the classical taxonomy, group 1
consists of individuals classified as P. alba, P. chilensis,
P. chilensis with leaflets smaller and hybrids between
two species, group 2 is formed by individuals classified
mainly as P. chilensis and group 3 corresponds to P.
chilensis and three individuals hybrids between this spe-
cies and P. alba. Group 4 is totally intermediate formed
by different types of hybrids (white by black carob or
vice versa) and group 5 consists mainly of P. nigra (Ta-
ble 3).
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Table 4 presents the average values of fruit and leaf
characters for each group and their respective coeffi-
cients of variation (in%) and in Table 5, the values found
T and R.
Table 3. Morphological composition of each group by number of tree, zone and classification according to classical taxonomy.
Groups Zone and Accession Number of individuals
1 Z1 = 1-4-5-24 (Pcxa), 2 (Pax?), 10-17-32 (Pcfm), 11-12-20-26 (Pa), 19 (Pc),
Z2 = 35-50 (Pc). Z3 = 44-46-63-64 (Pc), 57 (Pcfm). Z4 = 84 (Pa), 74-82 (Pc). 23
2 Z2 = 29 (s/ident), 33 (Pcfm), 37 (Pc). Z3 = 43-56-59-60-61-62(Pc),
38-45 (Pcfm). Z4 = 78 (Pcfm), 65-69-70-77-80 (Pc). 17
3 Z1 = 8 (Pcxa). Z2 = 36 (Pcxa ), 51 (Pc).
Z3 = 42 (Pcfm), 52 (Pax?). Z4 = 66-79(Pc). 7
4 Z1 = 3 (Pf o Pfxa)-21 (Pcxr)-22 (Paxn) -23 (Pafm). Z2 = 31(Pax).
Z3 = 39 (Pax)- 40 (Pcx?)-41 (Paxf)-53 (Pfxc). Z4 = 68 (Pfxc)-81 (Pcxf)-83 (Pcxf). 12
5 Z1 = 6 (Pf o Pfxa), 7-9-13-14-15-16-85(Pn). Z2 = 30-34-49-54(Pn).
Z3 = 48-58(Pn). Z4 = 67-71-72-73(Pn), 75-76(Pcxfon). 20
Total 79
Reference: in bold, individuals with intermediate characteristics according to the classification of Vascular Plants Laboratory at the University of Buenos Aires
Table 4. Average and coefficients of variation (CV) in percentage, by character and group.
1 17.48 28.38
0.62 13.15 4.86 2.77 1.07 1.38 2.82
2 17.85 28.73 0.62 13.74 4.89 2.85 1.08 1.36 2.79
3 16.55 25.73 0.66 12.98 5.51 2.39 1.36 1.29 2.50
4 17.51 22.48 0.79 11.17 5.79 1.97 2.51 1.87 2.17
5 14.74 17.40
0.86 8.66 6.43 1.38 2.34 3.06 1.98
1 14,83 13.34 13.72 10.22 13.35 15.89 23.19 32.17 6.86
2 16.26 8.02 12.44 11.79 12.64 14.13 21.92 30.46 7.16
3 11.92 16.75 10.91 7.54 8.67 12.84 35.04 37.95 19.46
4 13.37 14.00 11.30 9.87 12.24 13.51 20.99 14.86 11.02
5 12.50 13.35 10.62 13.05 13.48 19.98 20.06 23.87 8.42
1 34.84 103.23 4.03 25.76 15.07 1.56 4.09 9.75 1.04 1.00
2 41.22
122.45 3.60 23.02
20.31 1.56 5.36 13.04 2.24 1.94
3 33.90 104.96 3.79 24.73 16.05 1.61 4.40 9.80 2.57 1.71
4 29.62 94.73 3.40 24.88 10.66 1.54 4.09 7.09 1.50 1.50
5 27.49
66.08 3.71 25.11 5.59 1.21 2.56 4.77 1.75 1.65
1 22.80 13.86 14.18 18.44 34.71 13.01 27.81 33.80 19.98 0.00
2 20.80 14.42 13.89 15.55 14.15 10.73 15.88 17.29 40.42 12.49
3 24.50 19.77 13.85 23,63 53.40 11.53 53.41 46.26 20.79 44.10
4 26.92 16.30 28.29 32,74 41.43 36.99 39.44 34.56 34.82 34.82
5 28.16 19.27 14.47 12,25 33.88 10.33 22.88 46.93 35.24 30.38
Reference: Variables in bold are the variables that were selected to perform the discriminant analysis. CV: coefficient of variation.
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Table 5. Total differentiation of the characters (
T) and correlation coefficient (R) between the matrices of average morpho-
logical distance between groups and each one of the emerging ones for each character.
Leaf characters
T 0.893 0.889 0.820 0.767 0.748 0.723 0.636 0.320
R 0.773 0.847 0.600 0.780 0.389 0.817 0.590 0.150
Fruit characters
T 0.857 0.843 0.809 0.787 0.782 0.699 0.654 0.601 0.470
R 0.955 0.886 0.960 0.990 0.900
0.399 0.816 0.860 0.892
Branch characters
T 0.623 0.519
R 0.148 0.337
T 0.689
Reference: The R in bold represents significant values (P < 0.05) and variables in bold correspond to variables selected by Stepwise method.
The variables, which were subsequently selected for
the discriminant analysis, were the variables in bold.
Most were qualitative ordinals (ESPINA, SRAMA,
COLOR, BORDE Y FORMA), only three were quantita-
tive variables (NPIN, L/NART, AFR and L/AFOL). In
Table 4, it can be seen how the character of fruit color in
the morphological groups was distributed. Groups 1, 2
and 3 had white fruits (values close to 1) while groups 4
and 5 had darker fruit (values greater than 2). The grada-
tion in color coincided with the ordering of the morpho-
logical groups. In general it can also be noted that groups
3 and 4 showed intermediate values for most characters,
between groups 1 and 2 per side, and 5 on the other hand,
as extreme.
For those variables that were selected by the stepwise
method, the total differentiation of the characters (T)
was higher than 0.519, except for NPIN and FORMA,
which showed lower values. It should be noted that val-
ues close to 1 imply a greater degree of differentiation
provided by the character.
For the variables mentioned in the preceding para-
graph, it is observed that with the exception of variables
ESPINA, SRAMA and NPIN, the rest presented signifi-
cantly high correlation with the distance matrix of aver-
age morphological differentiation (Table 5).
3.1.2. Di s cr i minant Ana lysis
Of a total of 19 variables 9 were selected using the Step-
Fruit color was the first to contribute to group differ-
entiation, followed by the width of the fruit and the sinu-
osity of the branch. These three characters had a partial
R2 high (0.747, 0.51 and 0.442). Of these variables only
color and width of fruit showed relatively high values of
R and
T, while the sinuosity of branch showed an in-
T (Table 5).
Fruit and branch characters were those which have had
greater participation in the formation of the groups. Ta-
ble 6 shows the classification results, with an error rate
of 24%, meaning that the correct assignment to this clus-
ter structure is 76%. The groups that most influence had
on the rate of error were 3 and 4, due to the intermediate
characteristics of the individuals who compose them and
their high morphological diversity, whereas in the other
groups the degree of confusion was very low.
3.2. Discriminant Analysis for Character of
Offspring Sheet
It has been examined whether the offspring was due to
clusters in the mother plants obtained by discriminant
Since there was not enough data, two assessments
were made: one for leaf morphology variables and one
for variables included directly in the nursery: height at
different times, stem form and degree of thorns.
3.2.1. Discriminant Analysis for Character of Sheet
The method of Stepwise variable selection chose 8 of the
12 variables analyzed: LFOL, NPIN, ARFOL, AFOL,
To determine whether there was homogeneity of co-
variance between groups the modified Bartlett test was
applied. This test gave significant at 0.1%. This means
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that there is no homogeneity between groups covariance
so it was necessary to perform a quadratic discriminant
The total error rate of this analysis was very high
showing that it is not possible to group the progeny and
the mother plants in the same way (Table 7).
Thus, of the offspring of 23 mother plants belonging to
group 1, a large percentage confused with group 2 (41%)
and 4 (20%) and only 32% are in the group.
In the progeny of 17 individuals forming group 2,
there is a high percentage remaining in the same group
(70%). Most of the remaining 30% is confused with
group 1 (10%) and 5 (12%).
As for group 3, intermediate group with respect to the
average value of their characters, there is no individual in
that group.
In group 4, 18% of the individuals which forms it fo-
cuses in greater proportion on group 5 (53%) and 2
Finally, the descendants of group 5 are grouped by
85%, thus becoming the most stable group for these
3.2.2. D iscrimi n a nt Analys is for Variables Rec orded
in the Nursery
Of a total of 6 variables, Stepwise method selected 5
(Table 8), leaving aside the degree of thorniness.
As for leaf characters that were discussed above,
quadratic discriminant analysis was used, because there
was no homogeneity among the matrices covariance.
The error rate, considering these variables, also re-
mains high (0.5947). Thus, the offspring of the mother
plants belonging to group 1, a percentage of 58% fall in
group 1 and 32% in group 5 (Table 8).
Table 6. Percent of individuals belonging to each group and error rate for the groups formed.
Predicted group
Real group 1 2 3 4 5 Total
1 % 95.65 4.35 0.00 0.00 0.00 100
2 % 0.00 94.12 0.00 0.00 5.88 100
3 % 28.57 28.57 0.00 0.00 42.86 100
4 % 8.33 0.00 0.00 41.67 50.00 100
5 % 0.00 0.00 0.00 15.00 85.00 100
Total % 31.65 24.05 0.00 10.13 34.18 100
Jacknife error rate for formed groups
1 2 3 4 5 Total
Rate 0.0435 0.0588 1.0000 0.5833 0.1500
Priors 0.2911 0.2151 0.0886 0.1519 0.2531
Table 7. Percentage of individuals assigned by groups and error rate for the groups formed.
Predicted group
Real group 1 2 3 4 5 Total
1 % 32.17 40.87 1.30 5.65 20.00 100
2 % 10.59 69.41 1.76 6.47 11.76 100
3 % 12.86 38.57 0.00 11.43 37.14 100
4 % 5.83 20.00 2.50 18.33 53.33 100
5 % 2.15 6.45 0.54 3.23 84.63 100
Total % 14.43 35.44 1.29 7.73 41.11 100
Jacknife error rate for formed groups
1 2 3 4 5 Total
Rate 0.6783 0.3059 1.0000 0.8167 0.1237
Priors 0.2964 0.2191 0.0902 0.1546 0.2397
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Table 8. Percentage of individuals assigned by groups and error rate for the groups formed.
Predicted group
Real group 1 2 3 4 5 Total
1 % 57.50 6.64 3.04 0.95 31.88 100
2 % 39.73 9.07 5.07 0.53 45.60 100
3 % 36.31 10.12 7.74 1.79 44.05 100
4 % 37.75 8.43 2.81 2.01 49.00 100
5 % 14.55 2.73 0.91 0.45 81.36 100
Total % 14.43 35.44 1.29 7.73 41.11 100
Jacknife error rate for formed groups
1 2 3 4 5 Total
Rate 0.4250 0.9093 0.9226 0.9799 0.1864
Priors 0.2996 0.2132 0.0955 0.1416 0.2501
This behaviour is also observed in the offspring of the
individuals in group 2, 3 and 4, which give individuals,
which secrete primarily in groups 1 and 5.
The behaviour of the offspring of group 5 was differ-
ent, focusing on the same group (81%) and slightly on
group 1 (14%).
To summarize, it is fair to clarify that it was difficult
to bring together the descendants under the grouping of
the mother plants considering these characters, since
there is a high error rate.
The error of morphological leaf variables was pro-
vided with in a higher percentage by groups 1, 3 and 4,
while for the growth variables the groups that contributed
more error were 2, 3 and 4.
Table 9 shows the average and coefficients of varia-
tion for character and group for the variables studied in
the offspring.
The graphs of these measured variables on offspring
ordered by morphological group from the mother plants
show that despite the high degree of error found, some of
these variables allow groups to differentiate. Thus, the
length of leaflet in offspring of group 5 is of the lowest
value, while for the group of P. chilensis (group 2) is of
greater value.
Other interesting variables are the ratio of width to
length of leaflet and apex shape. The L/AFOL is also
greater in group 2 and then decreases towards the other
groups. As for the shape of the apex in group 5, it is more
rounded than the other groups that tend to be more acute.
3.3. Distribution of Morphological Groups by
Noting the distribution of morphological groups by zones,
Z1 (Santiago del Estero) is the most different; since the
morphological group 2 (P. chilensis) is absent. The re-
maining areas (Córdoba) have the 5 morphological
groups but in different proportions (Figure 7).
3.4. Study of the Association between Characters
of Seed Trees and Their Offspring
The relationship between the morphological groups of
harvested trees and offspring, as measured by canonical
correlation analysis, was conducted among a group of
mother’s morphological variables (with the exception of
type of branch) and the variable group of offspring for
each morphological group.
Although the data are presented together, each mor-
phological group had a canonical correlation analysis
independent from the other groups.
Most of the morphological groups needed two pairs of
canonical variables (L) to establish association between
variables groups of mothers and offspring, except for
group 3 in which this association was well defined with
only one canonical correlation (Table 10).
Even though all groups had a highly significant ca-
nonical correlation, the groups 3 and 4 were highlighted
presenting the highest values of R2 (Table 10). This cor-
relation indicates that the variability found in mothers is
strongly associated with the variability found in offspring,
in other words, the observed variability in both sets fol-
lows a certain order or relationship between pairs of sets
of variables.
Note that the linear combinations with correlation
maximum for each pair (L) and for each morphological
group were formed with different associations of vari-
ables for both the first set (morphological variables of
mothers) with the second set (morphological variables of
the offspring ).
Thus, it can be said that in the mothers set (Table 11),
for groups 1 and 2, morphological characters of fruit had
more weight than the characters of leaves, while for the
other groups involving both tpes of characters was eq- y
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Table 9. Average and coefficients of variation of offspring by character and group.
1 10.40 50.05 2.57 28.92 1.66 0.61 0.14 4.42 0.95
2 11.25 50.32 2.45 25.51 1.85
0.70 0.14 5.01 0.95
3 9.66 44.65 2.47 23.67 1.78 0.61 0.14 4.32 0.95
4 8.58 38.75 2.25 21.78 1.70 0.48 0.13 3.84 0.95
5 7.62 32.02 2.33 20.08 1.45
0.36 0.11 3.41 0.95
1 16.49 11.21 15.77 14.84 20.19 16.80 10.01 11.68 1.45
2 19.59 15.34 12.10 15.22 10.96 16.03 11.57 8.87 0.98
3 29.10 16.88 10.11 7.24 11.17 31.68 21.82 17.20 2.68
4 22.61 14.67 9.38 14.72 16.78 21.01 12.60 13.40 1.76
5 17.39 18.51 16.87 14.98 13.86 22.29 10.25 13.60 1.54
1 0.07 0.20 0.94 6.58 16.03 32.43 36.28 1.81 1.65
2 0.08 0.20 0.92 7.18 16.46 32.97 36.14 2.07 2.05
3 0.08 0.21 0.99 6.97 15.95 31.32 34.84 2.16 2.23
4 0.05 0.21 0.99 6.62 14.44 28.17 31.85 1.84 1.90
5 0.03 0.23 1.08 6.31 12.49 24.96 28.09 2.16 2.23
1 23.92 3.62 4.87 12.88 10.19 10.76 10.00 17.00 23.00
2 26.03 5.38 5.37 12.17 16.04 16.13 16.00 13.00 17.80
3 58.52 8.25 5.53 28.79 21.36 16.32 15.00 7.00 11.70
4 30.70 8.27 6.13 16.94 18.50 19.88 19.00 15.00 21.80
5 30.25 5.84 4.39 14.61 9.90 8.75 10.00 8.00 13.50
It is important to highlight that, when the associated
characters between seed trees and offspring coincide in
the distinct groups, this association keeps the same direc-
tion. Thus there is no evidence to indicate differences
between groups in the form of association between traits
The characters most involved in the linear combina-
tions were NART, EFR, LFOL, L/AFOL in three of the
five groups in the mother set, and LPIN and NFOL char-
acters in the offspring set. In the latter group LFOL was
distinguished, which appears in the five groups and it
also was a variable selected by stepwise method to per-
form discriminant analysis.
Most of the characters involved in the associations
have high values of coefficient of variation (Table 12).
The interpretation of these associations comes from
analysing each pair of canonical variables. So for the
Morphological group 1, the coefficients of linear com-
binations (Table 11) for the first partnership stated that:
fruits with thick and ratio width/thickness considerable in
mothers correlate significantly with offspring that had a
ratio length/width of leaflet higher, associated inversely
with the length of leaflet.
This would indicate, always in reference to the values
recorded in this morphological group that mothers with
large fruits in the dimensions of width and thickness tend
to provide offspring with leaflet of the smallest dimen-
sion in length, but wide.
The second axis showed that mothers with less number
of knuckles by fruit and with leaflet shorter in length
were significantly associated with offspring which had
longer pinnae but with fewer leaflet by pinnae.
Morphological group 2: For this group the first com-
bination of canonical variables was associated signifi-
cantly with greater fruit length and less number of
knuckles in mothers with a greater length of the pinnae
but with less number of leaflets in the offspring.
The second axis established that mothers with a
greater presence of thorns and fruit thinner had offspring
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Figure 7. Distribution of morphological groups by are a.
Table 10. Canonical correlation coefficients (R), the proportion of total variance explained by each pair of canonical variables
(R2) and associated probability levels (p-value) for each pair of canonical variables for each morphological group.
Grupo 1 2 3 4 5
L 1 2 1 2 1 1 2 1 2
R 0.72 0.55 0.68 0.67 0.94 0.82 0.68 0.75 0.60
R 2 0.51 0.30 0.46 0.45 0.89 0.67 0.46 0.57 0.37
p-valor* 1.4 × 109 4.7 × 103 7.4 × 1081.6 × 1045.3 × 1042.7 × 1073.7 × 103 5.3 × 1010 1.5 × 103
*p-valor 0.001 is considered highly significant.
with major length in leaflet and growth in height of seed-
lings in the last measurement (168 days old).
In this group the importance for the character and the
presence of thorns is emphasized. This has a high value
of coefficient of variation and occurs only in this group.
In the case of morphological group 3 it was observed
that the variability of the ratio length/width of leaflet and
its inverse association with the ratio length/number of
knuckles at the level of the mothers was significantly
correlated with the pattern of inverse association that
exists between length of leaflet and leaf area at the level
of offspring.
It could be inferred for this group that leaves with
leaflet of greater length than width, associated with a
higher number of seeds by fruit in mothers (or seeds
smaller for the same length of the fruit) will correspond
with offspring which have leaflet longest but lower leaf
Morphological group 4: the canonical first axis pre-
sented the canonical variables: length of leaflet and ratio
length/width of leaflet, associated inversely in set of
mothers and significantly correlated with the length of
leaflet which was, in turn, associated inversely with the
number and spacing of leaflet by pinnae for set of off-
The second canonical axis showed that the thickness
and the width/thickness of the fruit in mothers were cor-
related with the separation between leaflets associated
inversely with height growth of seedlings in the fourth
measurement date
It can be interpreted that mothers with long and wide
leaflets tend to give offspring with long leaflet but with a
fewer number of leaflet by pinnae and fewer separated.
Also, mothers with fruits with the width dimension
greater than the thickness will present offspring with less
separation of leaflet and less growth in height to 168
days-old of seedling.
Morphological group 5: For this group the ratio
width/thickness of the fruit associated with the ratio
length/width of leaflet in mothers, correlated with the
length of the pinnae and leaflet the offspring in the first
canonical axis, while the second was found that the
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Table 11. Coefficients of linear combinations of canonical variables (L) for characters of mothers and offspring, for each
morphological group. They indicate only the two largest absolute values for each group of variables.
Group 1 2 3 4 5
L 1 2 1 2 1 1 2 1 2
LFR 1.16
NART 1.90 0.96 1.3
L/NART 0.59
AFR 1.52
EFR 0.93 0.58 1.45
A/EFR 0.91 0.38
LFOL 1.74 0.75 1.2
L/AFOL 0.63 1.08 0.43
LPIN 1.09 1.00 0.75
NFOL 1.171.23 0.79
SFOL 0.93
LFOL 2.41 1.66 1.19 0.87 1.34
AFOL 1.57
L/AFOL 0.87 1.88
ARFOL 0.67
Growth ALT4 1.24 0.83
Table 12. Coefficient of variation of the characters involved in the canonical correlation for the mothers and offspring set.
Set Character
1 14.83
13.34 13.72 10.2213.35 15.89 34.71 33.80 19.98
2 16.26 8.02 12.44 11.7912.64 14.13 14.15 17.29 40.42
3 11.92 16.75 10.91 7.548.67 12.84 53.40
46.26 20.79
4 13.37 14.00 11.30
9.8712.24 13.51 41.43 34.56 34.82
Mother CV
5 12.50
13.35 10.62 13.0513.48 19.98 33.88 46.93 35.24
Set Character
1 11.21 14.84 20.19 16.80 10.01 11.68 23.92 10.00
2 15.34 15.22 10.96 16.03 11.57 8.87 26.03 16.00
3 16.88 7.24 11.17
31.68 21.82 17.20 58.52 15.00
4 14.67
14.72 16.78 21.01 12.60 13.40 30.70 19.00
Offspring CV
5 18.51 14.98 13.86 22.29 10.25 13.6 30.25 10.00
Reference: Variables in bold are the variables that were selected to perform the discriminant analysis and the numbers in bold indicate the variables that are part
of the canonical axes.
number of knuckles and leaflet length inversely associ- ated with the length of the fruit in the mothers, was cor-
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related with the length of leaflet and inversely with the
ratio length/width of leaflet in offspring.
Thus, mothers who have fruits with a greater dimen-
sion in width than in thickness and leaflet with more di-
mension in the long than in the width would give off-
spring with pinnae and longer leaflets.
4. Discussion
The use of numerical taxonomy is an essential tool for
morphological analysis and proper identification of ma-
terials used in this study. Thus, a total of 19 variables
used in this analysis were 9 the characters that contrib-
uted significantly to the construction of the morphologi-
cal groups of mothers. These were mainly fruit characters
(5) and branch (type of branch and thorns). The fruit
characters of higher correlation with the discriminant
functions estimated were the color and width of fruit. As
for the character leaves, the ratio length/width of leaflet
and the number of pair for pinnae were only considered.
Verga [11] found that characters ratio thickness/ width
of fruit, ratio length/width of leaflet and length of leaflet
were important for the differentiation of three morpho-
logical groups (P. flexuosa, P. chilensis and hybrids) in
the Chaco arid.
Also, Mantován [52] found that morphological differ-
entiation between populations of Prosopis flexuosa in the
Monte phytogeographic province was possible thanks to
the great weight variables had like length of leaflet and
the relationship between length of pinnae and width of
Moreover, Burghardt et al. [53] found that variables
such as length and width of pinnae and length of leaflet,
evaluated by principal component analysis, were suitable
to differentiate seedlings of 8 Prosopis species, grown
under uniform conditions.
In this study for morphological analysis of the off-
spring, 8 of the 12 variables were required and evaluated
at leaf level and 5 of the 6 variables were recorded in the
nursery to achieve adequate differentiation. Length of
leaflet along the width and area of the same variables
were the most important in the discriminant analysis.
From the morphological analysis of the mothers it was
possible to group the apparent morphological continuum
into five groups with an error level of 24%. This error
was primarily attributable to the variability in group 3
and less in group 4, both groups classified as intermedi-
ate. Groups 1 and 2 were the most homogeneous, since
the error rate was very low (4 to 5.6%), followed by
group 5 (15%).
By studying the seedlings in the nursery (offspring)
and trying to regroup under the classification for mater-
nal individuals it was observed that the error in the cor-
rect allocation increases, mainly in groups of intermedi-
ate characteristics.
Although the formation of these clusters in offspring
cannot be confirmed, multivariate analysis of canonical
correlation for each morphological group reflects the
morphological groups which best explain the variability
for each pair of canonical axes were groups 3 and 4 being
the most variable and presenting the highest values of R2.
These values indicate that the high variability found in
mothers is strongly associated with high variability found
in offspring, in other words, the observed variability in
both sets follows a certain linear relation, or one might
say, a continuous order.
At this level of analysis, variables such as those cited
by Burghardt et al. [53] are include. The length of the
pinnae, the number and length of leaflets in set of the
offsprings and for the set of mothers, the variables that
repeated the most in the different associations, were the
number of knuckles, the thickness of the fruit, length of
leaflet and the ration length/width of leaflet.
Each pair of canonical axes was different for each
morphological group, confirming identity of morpho-
logical groups.
The differentiation between populations in morpho-
logical groups in each region is linked to the fact that the
proportion of each morphological group in each area is
different as well as is the ecological and human condi-
In 1999, in zones 1 and 2 the livestock of cattle, goats
and sheep dominated over agiculture. The abundance of
Prosopis nigra confirms the existence of cattle that con-
siders this species little palatable and hence the percent-
age of this group is high (30%) in these regions.
Zone 3, apart from being in an ecotone between semi-
arid and arid region, this is an area where agricultural
activity was the greatest on livestock. Thus, according to
comments from the locals, the whites “algarrobos” were
left on seats and helmets stay, because they provided a
better shade and they were not attacked by drills, as it
happened with the black “algarrobos” (P. flexuosa and P.
nigra). On the other hand, the region 4 is a mixed pro-
duction area, where there is intensive agriculture (vine-
yards, olive and other fruit) in combination with large
cattle ranches.
Both regions are very disturbed by humankind. In
them; the native forest has been reduced to isolated
patches of adults or elderly individuals. In many cases
the larger individuals and portage have been left, which
the locals called “pantosos” and coinciding trees are
qualified within the intermediate groups, hence these
regions have the highest values of diversity, granted
mainly by such intermediate groups which continue to
mingle with the group of blacks and whites.
The morphological groups arising from the ordering of
Open Access AJPS
Morphological Diversity of Populations of the Genus Prosopis in the Semiarid
Chaco of Northern Cordoba and Southern Santiago Del Estero 2109
the mothers (determined by numerical taxonomy and
confirmed with a certain error of misclassification by the
discriminant analysis, both mothers and in offspring) are
homogeneous groups and it is considered that each of
them has a unique identity. This unique identity is not
consistent with the classification made from classical
The classical taxonomy in this study determined that
there are 16 taxa, while the morphological study sums it
up in 5 morphological groups [54,55]. While it is always
necessary to specify the scientific name of each group in
this study it is assumed, for the homogeneity of the mate-
rial, that group 1 consists of Prosopis alba, group 2 is
Prosopis chilensis, group 3 is a group of individuals of
intermediate characteristics between white “algarrobo”;
P. alba and P. chilensis; group 4 is formed by individuals
from classical taxonomy classified as hybrids between a
white and black “algarrobo” (P. flexuosa and P. nigra)
and group 5 consists of Prosopi s ni gra.
5. Conclusions
The “algarrobos”, present in the contact area of Prosopis
chilensis-P. flexuosa-P. alba-P. nigra in the Semiarid
Chaco of northern Cordoba and Southeast Santiago del
Estero, form morphologically defined groups.
Morphological studies of the offspring of the “algar-
robos” present in the contact area of Prosopis chilensis-
P. flexuosa-P. alba-P. nigra in the Semiarid Chaco of
northern Cordoba and Southeast Santiago del Estero con-
firm the existence of morphologically defined groups.
6. Acknowledgements
The autors wish to thank to Dr. Ramón Palacios
(Laboratorio de Plantas Vasculares de la Universidad
Nacional de Buenos Aires) for taxonomy determination.
They also acknowledge the IFRGV-CIAP-INTA. This
work was supported by Banco Nacional de Germoplama
de Prosopis and INTA Proyect 357.
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