Numerical Taxonomy of Combretum Loefl. from Southeastern Nigeria
Numerical taxonomic study of eleven Combretum Loefl. species common
in southeastern Nigeria was carried out based on morphological and anatomical
characters. PAST software was used to calculate the Euclidean distances and
the coefficients were clustered by unweighted pair-group clustering method (UPGCM).
From the 107 characters employed in the numerical analysis, the species were
separated into two broad clusters (C1 represented by C. zenkeri and
C2-the remaining 10 species). The clustering further suggested that there were
groups within the genus hence C2 separated into two subgroups with C. glutinosum,
a lone sub-cluster and the other nine species, which separated into four other
sub-clusters. The similarity coefficient among the Combretum species
studied ranged from 4.69 between C. mooreanum and C. bracteatum
to 8.72 between C. glutinosum and C. zenkeri. Generally, results
obtained favour species arrangement and clustering based on phylogenetic relationship
as in C. mooreanum, C. bracteatum and C. platypterum and
habitat preference. The unknown species, Combretum sp.1 is more closely
related to C. bracteatum than any other species studied. However,
C. constrictum, C. dolichopetalum, C. glutinosum, C. hispidum,
C. paniculatum, C. platypterum, C. racemosum and C.
zenkeri have been confirmed as individual taxa based on previous classifications.
Though each Operational Taxonomic Unit (OTU) is confirmed species, we assert
that the closeness observed amongst the OTUs imply that introgression as a mechanism
of speciation in the wild, is at play in the genus.
Received: October 13, 2013;
Accepted: January 15, 2014;
Published: February 27, 2014
Combretaceae is family of plant with 20 genera and 600 species, of tropical
and subtropical regions of the world (Gill, 1988). In
West Africa, the family Combretaceae is represented by 9 genera with 72 species
and the genus Combretum Loefl. is the largest genus with 49 species (Gill,
1988). Keay (1989) reported 25 species of the genus
Combretum Loefl. which are mainly straggling shrubs or lianes in Nigeria.
Hutchinson and Dalziel (1954) showed that a number of
species are indeterminate and occur in the South-Eastern Nigeria. The ethnopharmacological
importance which include anti-inflammatory, anthemintic, anti-biharzia (anti-schistosomal),
treatment of malaria, pain, dermatitis, diarrhea, Pneumonia, gonorrhea, syphilis,
hypertension and cancer have been reported (Coulidiati et
al., 2009; Fyhrquist et al., 2002; Baba-Moussa
et al., 1999; Simon et al., 2003;
Martini et al., 2004; Batawila
et al., 2005).
The existing information on these species in Nigeria is strictly based on morphological
descriptions by Hutchinson and Dalziel (1954). These
information were however, sourced from herbarium specimens. Literature search
revealed neither recent description nor taxonomic treatment of Nigerian members
of this genus. Hutchinson and Dalziel (1954) reported
indeterminate species and noted that much taxonomic gaps needed to be filled
with the identified species in tropical West Africa. This underscores the need
for a study approach that utilizes different taxonomic lines of evidence to
confirm the identity of species in southeastern Nigeria and other parts of tropical
West Africa. In the wild forest of southeastern Nigeria were the species occur,
there are conflicting identities with morphological signs of introgression.
Thus the study is aimed at resolving difficulties with identifying taxonomic
species from this section of Nigeria. It seeks to support the great taxonomic
work of Hutchinson and Dalziel (1954), which unarguably
is the taxonomic Bible of tropical West Africa. The numerical taxonomy approach
adopted for this study has been applied in the elucidation of complex genera
by Sornsuwan et al. (2006), Khalik
et al. (2008), Dogan et al. (2009)
and Osman et al. (2011).
MATERIALS AND METHODS
Plant material: Different specimens of Combretum were collected
from southeastern part of Nigeria (Fig. 1) between January
2009 and December 2011. By painstaking reference to the Flora of West Tropical
Africa (Hutchinson and Dalziel, 1954), these specimens
were sorted into ten known taxa and an indeterminate species (Table
|| Species name, locality, coordinates and date of collection
of Combretum species studied
Further authentication of the taxonomic identity of the species was achieved
by sending representative samples of each identified taxon to Forestry Herbarium
Ibadan (FHI). These specimens were compared with species from the study area
deposited at FHI. Morphological and epidermal studies were carried out on these
species and characters and their character states (Table 2)
deduced from the study were used for numerical analysis. Taxa were deposited
at the University of Port Harcourt Herbarium (UPH).
Character observation: In this study, the species were treated as the
Operational Taxonomic Units (OUT). Eleven OTUs (Table 1) and
one hundred and seven (107) characters derived from the morphology (anther colour,
flower colour, stem colour, colour of receptacle plus calyx tube, stem hair,
habit, number of wings, average leaf length, average leaf breath, average petiole
length, average internode length, leaf type, leaf apex, leaf base, leaf shape,
leaf surface and leaf arrangement) and anatomy (crystal type, crystal distribution,
number of palisade layers, No. of spongy layers, stomata types/complex/occurrence,
trichome type, anticlinal cell wall pattern and epidermal cell wall shape) (Table
2) of the species were used in constructing the dendrogram. These characters
were selected without prejudice. Ten samples of each authenticated OUT were
either qualitatively observed or quantitatively scored to deduce the results
summarized in Table 2.
Numerical analysis: Numerical taxonomic analysis was based on Sneath
and Sokal (1973). The hierarchical cluster analysis for qualitative and
quantitative characters was performed using binary Euclidean distance; the dendrogram
was drawn using average distance linkage (between groups). The similarity coefficient/Euclidean
distance were measured using PAST and clustered by Unweighted Pair-group Clustering
Method (UPGCM). Data generated from the different morphological and anatomical
characters were scored and converted to binary No. 1 or 0 i.e., present or absent
and fed into a computer which generated clusters of the OTUs according to their
overall similarity/Euclidean distance using PAST software. Dendrogram was constructed,
which represented the diagrammatic illustration of the relationship among the
species based on their degree of similarity in which the OTUs are linked together
at various levels of resemblance.
The characters and character states generated and used for the cluster analysis
is presented in Table 2. From the 107 characters employed
in the numerical analysis, the dissimilarity coefficients among the Combretum
species studied ranged from 4.69% between C. mooreanum and C. bracteatum
to 8.72% between C. racemosum and C. zenkeri (Table
3). At 11.54% dissimilarity as shown in Fig. 1, the OTUs
separated into two broad clusters. Cluster C1 contains only one species, C.
zenkeri while cluster C2 contains 10 species. However at 11.11% dissimilarity,
cluster C2 further separated into two sub-clusters (C3 with only C. glutinosum
and C4). Sub-cluster 4 gave rise to C5 and C7 each with two species and C6 with
five species (C. mooreanum, C. paniculatum, C. bracteatum,
C. platypterum and Combretum sp.1) as shown in Fig.
The unknown species Combretum sp.1 is closest to C. bracteatum
and together with C. mooreanum (all three in C9) occur in marshy environment.
C. mooreanum, C. bracteatum and C. platypterum in C6 are
phylogenetically related in Hutchinson and Dalziel (1954)
|| Character and character states used for cluster analysis
of Combretum species
|| Range of coefficient of dissimilarity matrix among the eleven
|1: C. bracteatum (Laws.) Engl. and Diels., 2: C.
constrictum (Benth.) Laws, 3: C. dolichopetalum Engl. and Diels.,
4: C. glutinosum Perr. ex DC., 5: C. hispidum Laws, 6: C.
mooreanum Exell., 7: C. paniculatum Vent., 8: C. platypterum
(Welw.) Hutch. and Dalz., 9: C. racemosum P. Beauv., 10: C.
zenkeri Engl. and Diels. and 11: Combretum sp.1
The close morphological similarities of members of the genus Combretum in
Nigeria oftentimes lead to confusion in species identification and collection.
Existing taxonomic information on the genus in the country is based on morphological
characters documented in Hutchinson and Dalziel (1954),
which reported some indeterminate species. Reassessment of the phylogenetic
relationship of members of this genus is therefore worthwhile. We have begun
this by subjecting species within the southeastern region of the country to
numerical analysis and phylogenetic interpretation.
Dendrogram based on morphological and anatomical information grouped these
eleven southeastern species into two major clusters C1 and C2. Cluster C1 is
distinct containing only C. zenkeri. This indicates that C. zenkeri
is distinct from all the other southeastern species studied. The remaining
ten species clustered in C2. The unknown species Combretum sp.1 is found
midway among these other species. In cluster C2, C. glutinosum is distinct
among the species in this cluster. C. racemosum and C. dolichopetalum
are closely related supporting Hutchinson and Dalziel
(1954). The relative closeness between these species is attributed to their
similar anatomical features. However, C. hispidum and C. dolichopetalum
did not follow the sequence.
||Dendrogram for the hierarchical cluster analysis of 11 southeastern
Nigeria Combretum species using Euclidean distance among the taxa
The divergence between these two species is as result of their anatomical differences.
Similarly, C. zenkeri and C. glutinonum are the most diverged
species in the dedrogram. On the other hand, the unknown species Combretum
sp.1 is more closely related to C. bracteatum and C. paniculatum
than any other species in the dendrogram. Based on their percentage dissimilarity,
Combretum sp.1 is a new unnamed species but more closely related to C.
It is important to reemphasize the fact that current information is lacking
on members of the genus Combretum in Nigeria. A closer comparative assessment
of the results obtained from this study with existing information in Hutchinson
and Dalziel (1954) confirm the phylogenetic relationship between C.
mooreanum, C. bracteatum and C. platypterum. In fact, C.
bracteatum is phylogenetically next to C. mooreanum in Hutchinson
and Dalziel (1954) classification key. These species also have similar habitat
preference occurring in marshy environments. C. constrictum, a low shrubby
liana also prefers damp habitats. However, C. glutinosum, which has been
previously reported as savannah small tree, was collected within the region.
So also was C. paniculatum, which reportedly thrive at the extreme of
the forest zone into the savannah region of the country. These may not be unconnected
with human dispersal of reproductive structures.
The close affinity observed in morphological and anatomical characters employed
in this study across species is worthy of note. These observations were highest
amongst members in C9 (C. mooreanum, C. bracteatum and Combretum
sp.1). We therefore assert that introgression as a mechanism for speciation
is at work on members of the genus Combretum in southeastern Nigeria.
Further work is ongoing for the authentication of this assertion.
Baba-Moussa, F., K. Akpagana and P. Bouchet, 1999.
Antifungal activities of seven West African Combretaceae used in traditional medicine. J. Ethnopharmacol., 66: 335-338.CrossRef | PubMed | Direct Link |
Batawila, K., K. Kokou, K. Koumaglo, M. Gbeassor, B. de Foucault, P. Bouchet and K. Akpagana, 2005.
Antifungal activities of five combretaceae used in togolese traditional medicine. Fitoterapia, 76: 264-268.CrossRef | Direct Link |
Coulidiati, T.H., H. Millogo-Kone, A. Lamien-Meda, C.E. Lamien and M. Lompo et al
Antioxidant and antibacterial activities of Combretum nioroense
Aubrev. Ex keay (Combretaceae). Pak. J. Biol. Sci., 12: 264-269.CrossRef | PubMed | Direct Link |
Dogan, B., A. Duran and E. Hakki, 2009.
Numerical analyses of wild Jurinea
spp. (Asteraceae) in Turkey. Bangladesh J. Bot., 38: 47-53.CrossRef |
Fyhrquist, P., L. Mwasumbi, C.A. Haeggstrom, H. Vuorela, R. Hiltunen and P. Vuorela, 2002.
Ethnobotanical and antimicrobial investigation on some species of Terminalia
(Combretaceae) growing in Tanzania. J. Ethnopharmacol., 79: 169-177.CrossRef |
Gill, L.S., 1988.
Taxonomy of Flowering Plants. Africana-FEP Publishers Ltd., Ibadan, Nigeria
Hutchinson, J. and J.M. Dalziel, 1954.
Flora of West Tropical Africa. Vol. 1, Part 1, Crown Agents for Oversea Governments and Administrations, London, UK., pp: 32-295
Khalik, K.N.A., M.M. Abd El-Ghani and A. El Kordy, 2008.
Numerical taxonomy of Galium
(Rubiaceae) in Egypt. Phytologia Balcacia, 14: 245-253.Direct Link |
Keay, R.W.J., 1989.
Trees of Nigerian. Clarendon Press, Oxford, UK
Martini, N., D.R.P. Katerere and J.N. Eloff, 2004.
Seven flavonoids with antibacterial activity isolated from Combretum erythrophyllum
(Burch) Sond (Combretaceae). S. Afr. J. Bot., 70: 310-312.
Osman, A., M. Zaki, S. Hamed and N. Hussein, 2011.
Numerical taxonomic study on some tribes of Gramineae from Egypt. Am. J. Plant Sci., 2: 1-14.
Sneath, P.H.A. and R.R. Sokal, 1973.
Numerical Taxonomy: The Principles and Practice of Numerical Classification. W H Freeman Limited, San Francisco
Simon, G., J. Dewelle, O. Nacoulma, P. Guissou, R. Kiss, D. Daloze and J.C. Braekman, 2003.
Cytotoxic pentacyclic triterpenes from Combretum nigricans
. Fitoterapia, 74: 339-344.PubMed |
Sornsuwan, P., T. Boonkerd and T. Seelanan, 2006.
Numerical taxonomy of some fern species in the genus Thelypteris
schmidel Sensu lato
in Thailand. BRT Res. Rep., 2549: 119-126.