American Journal of Plant Sciences, 2011, 2, 345-353
doi:10.4236/ajps.2011.23039 Published Online September 2011 (
Copyright © 2011 SciRes. AJPS
Infraspecific Delimitation of Acacia senegal
(Fabaceae) in Uganda
John Wasswa Mulumba1, Esezah Kakudidi2
1Plant Genetic Resources Centre, Entebbe Botanic Gardens, National Agricultural Research Organization, Entebbe, Uganda; 2School
of Biological Sciences, Makerere University, Kampala, Uganda.
Received May 6th, 2011; revised June 10th, 2011; accepted July 29th, 2011
The wide variation in Acacia senegal has presented taxonomic uncertainties and unresolved contradictions in previous
studies. In this study numerical taxonomic principles and multivariate analysis (UPGMA PCoA and PCA) were used
basing on 69 characters derived from growth form, branchlets, leaves, flowers, pods and seed. Three taxa, namely; va-
riety senegal, leiorhachis and kerensis have been discerned and described significantly improving the delimitations of
previous studies. The wid e variation within var. senegal has been sp lit into three recognizable variants an d that of var.
leiorhachis into two. The most important characters for differentiating the taxa include leaf breadth and length, pinna
length and its ratio to pinna breadth, number of leaflet pairs, petiolar gland shape, petiolar and rachis gland size, stem
and branch bark texture, stem and branchlet colour, under-bark colour for stem and branches, pod apical shape,
growth form, crown shape, and prickly state of leaves. An identification key has been constructed which, for the first
time, can be used to assign herbarium specimens to their respective taxa.
Keywords: Acacia Senegal, Infraspecific, Multivariate Analysis, Numerical Taxonomy, Uganda
1. Introduction
Acacia senegal (L.) Willd. was first described as Mimosa
senegal L. as far back as 1753 [1] before it was trans-
ferred to the present genus Acacia . The species belongs
to the sub-genus Aculeiferum which is known to be wide-
ly distributed in tropical and sub-tropical regions of the
Americas, Africa and Asia [2]. The great variability in
the species, however, has led to difficulty in its taxo-
nomic delimitation and hence a long list of synonyms.
Four varieties have been recognized, namely; var. sene-
gal Brenan, var. kerensis Schweinf., var. rostrata Brenan
and var. leiorhachis Brenan. However, these are sur-
rounded by continuous contradictions, disagreements [3-
5] and difficulty in assigning herbarium specimens to a
variety without adequate field notes about the habit and
habitat [6].
The delimitation of the botanical variation has been
based on morphological characters that differentiate the
varieties namely: presence or absence of hair on the in-
florescence axis, color of the axis, shape of pod tips,
number of pinnae pairs, occurrence of a distinct trunk,
and shape of the crown as provided in the variety key by
Brenan [4]. Despite this, there have been contradictions
and discrepancies in the character usage. The four varie-
ties are further reported to develop into different growth
forms [6] ranging from low multistemmed shrubs (var.
kerensis and var. rostrata), low bush with whip-like
stems (var. leiorhachis) small trees, (var. senegal and var.
rostrata) to larger trees (var. senegal and var. leiorha-
chis). The first numerical taxonomic study [7] based on
vegetative characters revealed that three of the four va-
rieties exist in Uganda but that their previous descrip-
tions were not sufficient to discern and delimit them. The
numerical taxonomic study, however, much as it im-
proved the descriptions of the three varieties, it was
based on only vegetative characters and it was not able to
provide characters that can be used to identify herbarium
The aim of the study was to confirm whether there are
distinct infraspecific taxa within A. senegal in Uganda. It
was further intended to find out whether the wide vari-
ability in the infraspecific taxa, which has been the cause
of taxonomic contradictions, can be further discerned
into recognizable groups. This would provide a compre-
hensive set of the best characters for differentiating the
infraspecific taxa hence developing a taxonomic identi-
fication key.
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda
2. Materials and Methods
2.1. Sampling and Specimen Collection
The study was undertaken in the cattle corridor of Uganda
during the period March 2007 to July 2008. The term
“cattle corridor” depicts the high concentration of live-
stock, particularly cattle, sheep and goats, in this area
compared to other parts of the country. The cattle corri-
dor stretches from the southern border of Uganda with
Tanzania, across the country to the northeastern part of
the country bordering Kenya and Sudan [7]. The corridor
comprises the rangelands (used in a broad sense to cover
grassland, bushland and woodland) which are variable in
ecosystem and vegetation types [8]. The corridor is fur-
ther characterized by the lowest rainfall in Uganda rang-
ing from lower than 500 mm to over 1000 mm in the less
dry areas [9]. Sampling followed the procedure outlined
by [10] whereby a location was taken to be an area with a
radius of 2.5 km. At each location identified, sampling
was done along a linear transect on mature plants which
were at least 50 - 100 m apart to minimize chances of
sampling very similar individuals. Five to fifteen mature
individuals per location were sampled per location re-
sulting into a total of 217 individuals. Three to five
branchlets were collected from each individual sampled
to provide enough material for the study and also for
herbarium specimens. The branchlets were immediately
pressed and the herbarium vouchers kept at Entebbe Bo-
tanic Gardens with duplicates deposited at Makerere
University Herbarium. Mature pods were harvested from
each tree sampled and kept separately in a cloth bag. At
dehiscence, not all the seed always fall out of the pod.
Therefore in cases where the pods were found to have
opened, as many pods as possible were collected to be
able to raise enough seed for the study as well as for
conservation. The seeds and pods from a given tree were
kept in the same bag. The seeds were treated with pesti-
cides in the lab to avoid insect damage and the lots for
conservation were processed and kept in the National
Genebank. Three to five inflorescences per tree were
collected and placed either in a test tube or polythene
tubing containing 95% ethanol. Inflorescences in full
bloom were harvested to avoid partially opened or wilt-
ing flower parts.
2.2. Characters Scored and Methods of Scoring
A total number of 69 characters were selected for the
study (Table 1) of which 11 were derived from the plant
habit, eight were from the branchlets, 17 from the leaves,
13 from the inflorescence/flower, 11 from the pods and
nine from the seed. Twenty nine of the characters were
qualitative and 40 were quantitative. The characters in-
cluded the ones used by [4,5,7,11] and from observations
made in this study.
Table 1. Characters scored for the study of Acacia senegal in Uganda.
I. Plant Habit
C1. Form: shrub (1); tree (2)
C2. Crown shape: lax-rounded (1); flat-spreading (2); open-irregular (3)
C3. Stem height (m)
C4. Stem diameter at base
C5. Stem height/diameter ratio
C6. Tree height (m)
C7. Bark colour: green-yellow (1); grey- brown (2); bright orange- brown (3); dull grey (4); grey-yellow (199D*) (5)
C8. Underbark colour stem: creamy-white (155D*) (1); brown (2); red (178A and B*) (3); dark pink (181D*) (4)
C9. Underbark colour branch: creamy-white (155D*) (1); brown (2); red (178AandB*) (3); dark pink (181D*) (4)
C10. Stem bark texture: papery and peeling (1); smooth, not papery and peeling (2); fissured (3); flaking (4)
C11. Branch form: Straggling (1); straight (2); whippy (3)
II. Branchlets (scores done between 20 and 30 cm from tip)
C12. Colour: yellowish (1); greyish-brown (2); purplish-brown (3) purplish-black (4); purplish-grey (5)
C13. Hairiness: glabrous (1); sub-glabrous (2); pubescent (3); densely pubescent (4)
C14. Bark texture: papery and peeling (1); papery and not peeling (2); not papery and not peeling (3)
C15. Internodal length (cm)
C16. Number of nodes (between 20 and 30cm from tip)
C17. Vertical prickle length (mm)
C18. Downward prickle length (mm)
C19. Ratio of upward to downward prickle length
III. Leaves (at 20 to 30 cm from tip)
C20. Leaf length (cm)
C21. Petiole length (cm)
Copyright © 2011 SciRes. AJPS
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda347
C22. Leaf/petiole ratio
C23. Leaf width (cm) at widest point
C24. Pinna length (cm)
C25. Pinna breadth (cm) at widest point
C26. No. of pinnae pairs
C27. No. of leaflet pairs
C28. Petiolar gland: present (1); absent (2)
C29. Petiolar gland length (µm)
C30. Petiolar gland breadth (µm)
C31. Petiolar gland shape: circular (1); oblong (2)
C32. Glands on rachis: absent (0); 1 (1); 2 (2); 3 (3)
C33. Rachis gland length (µm)
C34. Rachis gland breadth (µm)
C35. Hairiness: pubescent (1); glabrous (2); sub-glabrous (3)
C36. Midrib spines: absent (0); 1 (1); 2 (2); 3 (3)
IV. Inflorescence
C37. Inflorescence colour: white (1); cream (2)
C38. Spike length (cm)
C39. Peduncle length (cm)
C40. Spike/peduncle length ratio
C41. Hairiness of axis: glabrous (1); glabrous except for a few basal hairs (2); pubescent (3); densely pubescent (4)
C42.Corolla colour: white (1); cream (2)
C43. Corolla length (mm)
C44. Corolla/calyx ratio
C45. Calyx colour: green (1); purplish-green (2); red (3)
C46. Calyx length (mm)
C47. Calyx hairiness: glabrous (1); sub glabrous (2); pubescent (3)
C48. Stamen filaments length (mm)
C49. Pistil length (mm)
V. Pod
C50. Pod shape: oblong (1); elliptic (2)
C51. Pod color: grey (1); grey-yellow (2); grey-brown (3); yellowish-brown (4); brown (5)
C52. Pod length (cm)
C53. Pod width (cm)
C54. Pod apical shape: acuminate (1); acute (2) rostrate (3); rounded (4)
C55. Hairiness: densely pubescent and not appressed (1); sparsely pubescent and not appressed (2); densely pubescent and appressed (3);
sparsely pubescent and appressed (4); puberous
C56. No. of seeds per pod
C57. Pod venation: pronounced (1); not pronounced (2)
C58. Pod thickness: papery (1); thick (2)
C59. Pod outlook: flat (1); bulging over seed (2)
C60. Surface protrusions: present (1); absent (2)
V. Seed
C61. Seed colour: yellow (1); grey-brown (2); brown (3)
C62. Seed length (mm)
C63. Seed width (mm)
C64. Seed apical shape: rounded (1) acute (2)
C65. Pleurogram colour: yellow (1); grey-brown (2); brown (3); dark brown (4)
C66. Pleurogram length (mm)
C67. Pleurogram breadth (mm)
C68. Pleurogram shape: broadly open (1); nearly closed (2)
C69. Funicle length (mm)
*Corresponding colour chart number from Standard Royal Horticultural Society (2001) colour chart.
Copyright © 2011 SciRes. AJPS
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda
Three flowers from each of three inflorescences were
randomly selected and scored making a total of nine
flowers scored per individual tree. Flowers were dis-
sected under a microscope over a graduated graticule (in
micrometers) to allow for measurements to be taken di-
rectly. Five mature and complete pods randomly picked
from the lot were scored from each individual tree. Pod
length was taken from the point of attachment to the stalk
to the apex tip. Pod width was taken at mid-length of the
pod. Pod surface protrusions (appearance of a pro-
nounced pattern at the seed positions) were scored as
present or absent. The seeds per pod were taken as the
average from three pods. The shape of the pleurogram
was scored on two character states, thus; broadly opening
or nearly closed. Funicle length was taken as measure-
ment from the point of attachment on the pod to the point
of attachment on the seed. Data on colour shades was
taken using the Royal Horticultural Society [12] colour
chart. As much as possible colours were scored on
freshly harvested seeds to reduce effect of aging on col-
2.3. Data Analysis
The NTSYSpc (Numerical Taxonomy and Multivariate
Analysis System version 2.1e; J. F. Rohlf, 2000) was
used for the analysis. Raw data was first standardized
using range for quantitative characters and standard de-
viation for qualitative characters. Cluster analyses were
performed separately for the qualitative and the quantita-
tive characters based on UPGMA. Levels of similarities
and dissimilarities were computed using Eucledean coef-
ficients for quantitative data, Simple Matching for multi-
state and Manhattan coefficients for binary qualitative
data. Cophenetic correlation coefficients were calculated
to examine the goodness of fit of the cluster analysis to
the matrices. Quantitative data was further analysed us-
ing Principal Component Analysis (PCA) based on simi-
larities derived from product moment correlation coeffi-
cient while qualitative data was further analysed using
Principal Coordinate Analysis (PCoA) based on Simple
Matching coefficient derived dissimilarities/similarities.
Individuals in the resulting clusters were re-analysed
separately to further discern the variation within each
cluster. Univariate statistics for major discriminating
quantitative characters were computed against the emer-
gent groupings based on qualitative data and presented in
form of box-plots.
3. Results
3.1. Analysis Based on Qualitative Data
The results based on PCoA as well as UPGMA are sug-
gestive of three distinctive clusters; cluster A, B and C
(Figures 1 and 2). The first principle component is re-
sponsible for separating cluster B and C while the second
principle component is more responsible for separating
cluster A and B. The re-analysed cluster B revealed three
sub-clusters; sub-cluster 1, 2 and 3 (Figure 3) while
cluster C revealed two sub-clusters under cluster and
ordination analyses (Figure 4). The most important
characters in explaining the observed variation (charac-
ters with high loadings) included stem and branch bark
texture, stem and branchlet colour, under-bark colour for
stem and branches, pod apical shape, growth form, crown
shape, calyx colour, pleurogram colour and prickly state
of leaves. Cophenetic correlation coefficients for the
simple matching coefficients plotted against their tree
matrices ranged between 0.84 and 0.89 indicating good
fit [9].
Figure 1. A 2-D plot of 217 individuals of Acacia senegal
showing principal coordinates 1 and 2 derived from princi-
pal coordinate analysis based on 14 multistate characters.
Figure 2. Phenogram of UPGMA clustering of Simple Match-
ing coefficient based on 14 multistate characters and 217
individuals of Acacia senegal. Cophenetic correlation coeffi-
cient (r = 0.84).
Copyright © 2011 SciRes. AJPS
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda349
-0.8 -0.6 -0.4 -0.2 0.0 0.20.4 0.6
PCo 3
PCo 1
PCo 2
Figure 3. A 3-D plot of 143 individuals of Acacia senegal var.
senegal showing principal coordinates 1, 2 and 3 derived
from principal coordinate analysis based on 14 multistate
PCo 3
PCo 1
PCo 2
Figure 4. A 3-D plot of 66 individuals of Acacia senegal var.
leiorhachis showing principal coordinates 1, 2 and 3 derived
from principal coordinate analysis based on 14 multistate
3.2. Analysis Based on Quantitative Data
The PCA based on the forty quantitative characters dis-
played a wide variability but the first four components
explained less than 40% of the total variation. No clear
clustering of individuals was displayed. The PCA using
19 characters selected from the first analysis based on
their relatively higher loadings equally displayed great
variation in the individuals with minimal clustering
(Figure 5).
The first and second principal components explained
43% of the total variation while the first four components
explained 63% and the first six components explained
77%. The key characters responsible for the variation
along PC1 (Table 2) were tree height and stem diameter
at ground level (DGL), leaf breadth, leaf length, pinna
length, the ratio of pinna length to pinna breadth, number
of leaflet pairs, size of petiolar glands and peduncle
length. Leaf breadth and length, pinna length and its ratio
to pinna breadth, and number of leaflet pairs had load-
ings of 0.7 and above suggesting that they were of higher
importance in explaining the variation along PC1. The
characters responsible for the variation along PC2 relate
to size of petiolar and rachis glands and seed length. In-
ternodal length, the related number of nodes per unit
length, and length of upward prickles were responsible
for the variation along PC3 while size of flower parts,
namely, filament length and pistil length were responsi-
ble for the variation along PC4.
The results of the cluster analysis based on UPGMA
agreed with the ordination results. Box plot analysis
(Figure not shown) however, showed a high degree of
overlap of characters across the groupings making it dif-
ficult to use them independent of qualitative characters.
4. Discussion
The taxonomic delimitation of Acacia senegal infras-
pecific taxa has been a source of contradiction and un-
certainties due to the wide variation there-in [3-5,11,14,
15]. Although our previous study [7] reduced the delimi-
tation uncertainties, it relied on only vegetative charac-
ters and the key developed could not be used to differen-
tiate herbarium specimens; neither could it clarify on
PC 1
-1.0-0.8-0.6-0.4-0.20.0 0.2 0.4 0.6 0.8 1.0
PC 2
Figure 5. A 2-D plot of 217 individuals of Acacia senegal
showing principal component 1 and 2 derived from princi-
pal component analysis based on 19 quantitative characters.
Copyright © 2011 SciRes. AJPS
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda
Copyright © 2011 SciRes. AJPS
Table 2. Character loadings for the Principal Component Analysis based on Product Moment Correlation Coefficient for
quantitative characters.
Character PC 1 PC 2 PC 3 PC 4
C4 0.6567
0.2177 0.1206 0.1343
C6 0.6458
0.2881 0.1226 0.0332
C15 0.4334 0.0261 –0.6725 –0.4541
C17 –0.0919 0.1359 –0.5030 0.1437
C20 0.7040 –0.0490 0.0521 0.0124
C21 0.8620
0.1006 0.1467 –0.0191
C24 0.8787
0.1139 0.1410 0.0023
C30 0.5198 –0.7355
0.0607 0.1111
C33 0.5637
0.7328 –0.0723 0.1108
C34 0.5779
0.7405 –0.0576 0.0857
C39 0.5762
0.1283 0.0094 –0.1729
C48 0.2408 0.0981 –0.3735
C49 0.0745 0.0962 -0.3582
C62 0.3462 0.5329 –0.0131 0.0584
C63 0.3385 0.4335 –0.0673 0.1518
C19 –0.4314 –0.0657 0.7021 0.4400
C27 0.7920
0.2128 0.1239 –0.0785
variability within-in a given variety. The aim of the study
was to confirm whether there are distinct infraspecific
taxa within A. senegal in Uganda and to find out whether
the wide variability at the infraspecific level, which has
been the cause of taxonomic contradictions, can be fur-
ther discerned into recognizable groups. This would pro-
vide a comprehensive set of the best characters for dif-
ferentiating the infraspecific taxa hence developing a
taxonomic identification key suitable for field and her-
barium use.
4.1. Infraspecific Groupings
The findings of this study have shown effective delimita-
tion of six groups at two levels. The first level of differ-
entiation (Figures 1 and 2) defined the previously known
three varieties of A. senegal namely; var. kerensis (clus-
ter A), var. senegal (cluster B), and var. leiorhachis
(cluster C) and confirmed their presence in Uganda.
The variety kerensis is here described as mainly a shrub
(2.1 - 5 m ht.) with a lax-rounded to mainly open irregu-
lar crown. It has a papery and peeling, green-yellow stem
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda351
bark and dark pink underbark. The branches are domi-
nantly straggling with a dark pink underbark colour
while the branchlets are mainly papery and peeling with
some individuals peeling but not papery. Leaves are
dominantly prickly with leaf breadth (1.43 - 6 cm), pinna
length (0.86 - 2.1 cm), number of leaflet pairs (10 - 14
{16}) and number of pinna pairs (3 - 4). The taxon bears
characteristically more oblong than circular petiolar
glands of length (4.0 - 7.4 µm) and breadth (2 - 3.4 µm)
while the rachis glands length varies from 3 to 4.4 µm
and breadth from 2 to 2.8 µm. The taxon therefore has
petiolar glands whose length to breadth ratio is 2.0
making the glands characteristically more oblong than
circular. The calyx is purplish-green to red and the pods
bear mainly rounded apical shapes.
This description fits and even improves the previous
descriptions of the variety kerensis [4,7]. Figure 1 also
clearly brings out the closer relationship between this
variety and var. senegal (cluster B) which could have led
to the conclusion by [11] that the two varieties blend into
each other and are therefore one variety.
The variety senegal is here described as mainly a tree
with some shrubs, (1.8 - 7.1 m ht.) with a very variable
crown shape (lax-rounded, flat spreading to open irregular).
The stem bark is papery and peeling to fissured, green-
yellow, but also grey-brown, dull grey and occasional
bright orange brown, while the underbark is cream-white,
dark pink but predominantly dark pink. The branches are
straight to straggling, papery and peeling while the young
branchlets are yellowish to purplish black. The leaves are
seldom prickly, with a leaf breadth of 2.1 - 3.8 cm, pinna
length of 1.3 - 2 cm, number of leaflet pairs 12 - 15 (16)
and number of pinna pairs (3 - 5). The petiolar gland
length varies from 4.0 to 5.8 µm while the breadth varies
between 2.0 and 3.2 µm. The rachis gland length is 3.4 -
4.4 µm while the breadth is 2 - 3.2 µm. The calyx is pur-
plish-green and the pods apices acute to rounded. This
description agrees with and further augments the findings
of [7,11]. Neither the degree of pubescence on the bran-
chlets nor on the inflorescence axis, which were used
ambiguously by earlier studies [14] to separate the varie-
ties, has been found to be important in this study. No
wonder [3] retracted this position and later conceded [4]
together with [5] that the taxonomy of the species was far
from clear. This study has therefore provided better de-
limitation of the taxon significantly removing previous
From these findings, Acacia senegal var. leiorhachis
can be described as a tree (4.2 - 13.9 m ht.) with a lax-
rounded to flat spreading crown. The stem bark is fis-
sured, grey-brown to dull grey whereas the underbark is
red. The branches are straight to straggling, purplish-grey
to purplish-black, papery and peeling, peeling and not
papery, to papery and not peeling with a red underbark.
The leaves are seldom prickly with leaf breadth (2.7 - 5.6
cm), pinna length (1.7 - 3.26 cm), number of leaflet pairs
(16 - 20) and pinna pairs (4 - 5). The petiolar gland
length varies between 2.4 and 5.4 µm while the breadth
varies between 2.4 and 5 µm and characteristically more
circular than oblong. The rachis gland length varies be-
tween 2.6 and 4.6 µm and the breadth from 2.0 and 4.2
µm. The calyx is purplish green while the pod apical
shape is acute to round. The description agrees with and
complements that of [7] together with the arguments
thereof. Due to the absence of sufficiently distinguishing
characters on herbarium specimens, [15] decided that the
differences between A. senegal and A. circummarginata
were not distinct and merged the two into A. leiorhachis.
The present study has identified characters that can be
used to distinguish the different taxa in herbaria (as well
as in the field) thus agreeing with [5,11] that the taxa are
distinct. However, [11] preferred to maintain this taxon
as a species (A. circummarginata) following [3] as op-
posed to a variety (leiorhachis) as given by [5] and sub-
sequently followed by [3]. Our opinion based on the
findings of this study is that this taxon (var. leiorhachis)
as well as var. senegal are better treated as varieties of A.
The second level of taxonomic differentiation delim-
ited three groups from var. senegal (Figure 3) and two
from var. leiorhachis (Figure 4). The three groups de-
limited from var. senegal can be described as follows.
The first group, represented as cluster 1 (Figure 3), pre-
sents as a tree with a lax-round crown, fissured green-
yellow stem bark, yellowish papery and peeling bran-
chlets, purplish-green calyx and round pod apices. The
second group, represented as cluster 2, differs from the
first one by having dull-grey to grey-brown, papery and
peeling stem bark, purplish-black branchlets, and acute to
acuminate pod apices. This group was most dominant.
The third group, represented as cluster 3, presents as a
shrub with flat spreading to open irregular crown.
The two groups delimited from var. leiorhachis (Fig-
ure 4) can be described as follows; the first presents as a
tree with grey-brown stem bark and mainly straight
branches while the second one presents as a tree with
dull-grey stem bark and straggling branches.
The groups delimited at the second level of differen-
tiation can be based described as variants of variety
senegal and leiorhachis respectively agreeing with [6]
that varieties of Acacia senegal can develop into differ-
ent growth forms. A taxonomic key is hereby presented
but since the individuals studied were from only Uganda,
the key cannot be treated as a universal one until similar
studies are done across the species range of occurrence.
The ecological significance of this differentiation will be
further investigated in our subsequent study.
Copyright © 2011 SciRes. AJPS
Infraspecific Delimitation of Acacia senegal (Fabaceae) in Uganda
Copyright © 2011 SciRes. AJPS
Proposed taxonomic key
1. Plant a tree------------------------------------------------------------------------------------------------------------------------------2
1. Plant a shrub or bush------------------------------------------------------------------------------------------------------------------5
2. Tree height 4 - 14 m, bark fissured, underbark red, young branchlets purplish-grey to purplish-black, leaf breadth 2.7 -
5.6 cm, pinna length 1.7 - 3.3 cm, number of leaflet pairs 16 - 20, petiolar gland shape more circular than oblong,
petiolar gland length 2.4 - 5.4 µm, petiolar gland breadth 2.4 - 5 µm, rachis gland length 2.6 - 4.6 µm, rachis gland
breadth 2.0 - 4.2 µm----------------------------------------------------------------------------------------------------------------------3
2. Tree height 2 - 7 m, bark papery and peeling to fissured, underbark dark pink, young branchlets yellowish to pur-
plish-black, leaf breadth 2.1 - 3.8 cm, pinna length 1.3 - 2.0 cm, number of leaflet pairs 12 - 16, petiolar gland shape
oblong, petiolar gland length 4 - 5.8 µm, petiolar gland breadth 2.0 - 3.2 µm, rachis gland length is 3.4 - 4.4 µm and
rachis gland breadth 2 - 3.2 µm---------------------------------------------------------------------------------------------------------4
3. Stem bark grey-brown, branches mainly straight--------------------------------------------------------------Var. leiorhachis1
3. Stem bark dull-grey, branches straggling-----------------------------------------------------------------------Var. leiorhachis2
4. Branchlets yellowish papery and peeling, pod apices round------------------------------------------------------Var. senegal3
4. Branchlets purplish-black and peeling, pod apices acute to round (variable)----------------------------------Var. senegal4
5. Crown flat spreading to open irregular, stem bark papery and peeling mainly green-yellow, underbark red, branchlets
purplish-black papery and peeling to peeling and not papery, petiolar gland length (3.2 - 4.4 µm)-----------Var. senegal5
5. Crown Lax-round, underbark dark pink, branches dominantly straggling, Leaves dominantly prickly, leaf breadth
(1.4 - 3.6 cm), pinna length (0.86 - 2.1 cm), number of leaflet pairs (10 - 14 {16}), number of pinna pairs (3 - 4),
petiolar gland shape oblong, petiolar gland length (4.0 - 7.4 µm) and breadth (2 - 3.4 µm), rachis glands length (3 - 4.4
µm), and breadth 2 - 2.8 µm, calyx purplishgreen to red, pods with mainly rounded apices----------------Var. kerensis
1 and 2 are two groups that have emerged out of var. leiorhachis while 3, 4 and 5 have emerged out of var. senegal as variants.
4.2. Usefulness for Identification of Herbarium
One of the problems in studying this species has been
difficulty in identification of herbarium specimens with-
out adequate field notes. This study has revealed that
characters, namely; size of glands, particularly petiolar
gland length and breadth and their ratio which ultimately
determines their shape; number of leaflet pairs; leaf
breadth and pinna length; colour of branchlets; prickly
nature of leaves and to a lesser extent number of pinna
pairs can be important characters for differentiating her-
barium specimens and assigning them to their respective
taxa. This study further confirms that quantitative char-
acters overlap in this species as earlier reported [4,7,11].
This resulted in groups of clusters which although not so
taxonomically important by themselves, the analysis was
essential in identifying the most important quantitative
characters which have formed the bulk for the overall
taxonomic delimitation and in particular for the identifi-
cation of herbarium specimens.
5. Acknowledgements
The Swedish International Development Corporation
Agency (Sida) through the East African Plant Genetic
Resources Network (EAPGREN) is greatly appreciated
for the financial support to this study.
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