Abstract:
The genus Phyllanthus (Phyllanthaceae) is of economic importance in herbal medicine
and owing to its diversity, grows in similar habitats and shares common local names in
Nigeria. These common local names give rise to misidentifications and taxonomic
confusion. The only available taxonomic information on Phyllanthus is the Flora of West
Tropical Africa which is not current. Therefore, this study was conducted to provide
revised taxonomic information on Phyllanthus species and a reliable key for their
identification.
One hundred and forty two specimens comprising 55 field collections covering major
ecological zones in Nigeria and 87 representative herbaria materials from Forest
Herbarium Ibadan, University of Ibadan herbarium and Obafemi Awolowo University
herbarium were assessed for morphological characters using standard taxonomic
methods. Light and Scanning Electron Microscopes were used to examine leaf epidermal
and pollen morphology. Genomic DNA from 20 fresh and field collected young leaf
samples was extracted, amplified using chloroplast rbcL primer and the product was
sequenced using standard techniques. Phylogenetic trees were constructed using
maximum composite likelihood based method. Principal Component Analysis (PCA) and
cladograms of the assessed characters were used to establish taxonomic relationships
among the taxa. Data were subjected to descriptive statistics.
Nineteen Phyllanthus species were recognised from the herbarium materials out of which
16 species were validated because Phyllanthus floribundus, P. fraternus and P.
physocarpus were synonyms of P. muellerianus, P. amarus and P. acidus, respectively.
The length and width of leaves ranged from 0.45 - 11.70 cm and 0.15 - 5.40 cm,
respectively. The leaves were entire with alternate arrangement and the leaf shapes were
mainly oblong, lanceolate and linear. Only P. muellerianus had recurved stipular spines
at the nodal points. Perianth lobes ranged from 4-6 and were mainly green. Fruits were
green except in P. acidus (yellow), P. muellerianus (red), P. reticulatus (black) and P.
urinaria (reddish-brown). Epidermal cells were mostly irregular/polygonal on adaxial
and/or abaxial surfaces but rectangular in P. muellerianus and P. floribundus. Stomata
iii
were anisocytic, anomocytic, laterocyclic and paracytic. Epicuticular wax deposits,
sessile multicellular scales, unicellular trichomes, oil droplets, crystal sand and druses
were recorded in all except P. maderaspatensis, P. mannianus, P. nigericus, P.
niruroides, P. pentandrus, P. sublanatus and P. urinaria. Pollen was 3-colporate, finely
reticulate, prolate, subprolate and oblate-spheroidal, while the size ranged from small
(12.40 x 13.00 µm) to medium (31.50 x 23.25 µm). Four clusters and clades each were
delineated from the PCA and cladograms, respectively indicating that the genus is
paraphyletic, contrary to the presumed monophyletic relationship of the species. A
dichotomous key was produced for easy identification of the species.
Sixteen Phyllanthus species were established and revised taxonomic information revealed
clusters useful in understanding the relationships among the species of Phyllanthus in
Nigeria.