Stem anatomy of some members of the subfamily papilionoideae with reference to their identification

Quantitative and qualitative data are presented for ten species in the subfamily Papilionoideae in Ile-Ife, Nigeria with the view to document the stem characters of taxonomic value and that could be used in identifying the species within the subfamily. Species studied were Desmodium tortuosum (Sw.) DC., Desmodium scorpiurus (Sw.) Desv., Desmodium adscendens (Sw.) DC., Cajanus cajan (L.) Millsp., Calopogonium mucunoides Desv., Centrosema molle (Mart.) ex. Benth., Mucuna pruriens (Linn.) Walp., Vigna unguiculata (Linn.) Walp., Crotalaria retusa Linn. and Gliricidia sepium (Jacq.) Walp.
The stem anatomy of the species was studied by cutting the Transverse, Tangential Longitudinal as well as Radial Longitudinal Sections of the stem. with a Reichert microtome at a thickness of ten micrometre. Schultz’s fluid was used for the maceration of wood.
Circular and undulating stem outline is diagnostic and unique for Centrosema molle while oval pith shape through the Transverse Section of the stem is also unique to Centrosema molle and Vigna unguiculata. Pith is central in all the other species studied except in Mucuna pruriens and Vigna unguiculata. Cajanus cajan is the only species with angular collenchyma cells in the cortical region. Axial parenchyma is generally paratracheal and range from scanty to banded confluent. Wood is generally diffuse porous. Vessel pore shape is generally oval to circular in shape except in Desmodium adscendens, Mucuna pruriens, Vigna unguiculata and Centrosema molle where they are largely circular to oval. Presence of tyloses in the vessels delimit Glyricidia sepium from all the other species studied.
Vessel length and diameter study suggest primitiveness of the vessels in Vigna unguiculata while they are more advanced in Mucuna pruriens. Among the three species of Desmodium studied, Desmodium scorpiurus seems to be more advanced and Desmodium tortuosum least advanced in stem characters. Homogeneous wood rays in the Tangential Longitudinal Section of the stem suggest that Cajanus cajan and Gliricidia sepium are more advanced in terms of wood rays than the other species. The dendrogram of both qualitative and quantitative data distinctly separates Crotalaria retusa from other species. Type of stem, presence of central hollow at the pith and vessel width are the major characters unique to Crotalaria retusa. Desmodium tortuosum is delimited in the second major cluster largely because of its non-storied fibres and heterogeneous wood rays which are primitive characters. The study has also revealed a close relationship in stem anatomy between Desmodium adscendens and Calopogonium mucunoides; between Desmodium scorpiurus and Centrosema molle; and between Cajanus cajan and Gliricidia sepium.