TAXONOMIC REVISION IN THE GENUS COLA SCHOTT. AND ENDL. IN NIGERIA

Abstract

Cola Schott.&Endl.is a genus of about 125 species of which about 31 species are available in Nigeria. The species play vital roles in social, cultural, religious and commercial lives of Nigerians. There has been no comprehensive systematic approach to the taxonomy of Cola and identification of the various species has been difficult. The aim of the study was to revise the genus Cola in Nigeria for easy identification and classification. Twenty one species of Cola found mainly in the forests of southeastern Nigeria were studied. Specimens (147) in the herbaria of the Forestry Research Institute of Nigeria, Ibadan, University of Ibadan and Ahmadu Bello University, Zaria were also examined. Selected vegetative and reproductive characters were assessed and leaf epidermal morphology as well as transverse sections of the leaf blade and petiole were done using standard methods. Pollen morphology was studied using the Erdtmanacetolysis method. Photomicrographs were obtained using a camera-mounted microscope. Phytochemical screening of the leaves was carried out following standard methods for alkaloids, anthraquinones, saponins, terpenes, sterols, flavonoids, resins, balsams and tannins. Principal components analysis and dendrograms of the characters were constructed to elucidate taxonomic relationships among the taxa. Leaves were mainly glabrous but sometimes hispid, scabrous and tomentose and might be lobed, elliptic, ovate or oblong in shape. C. anomala had three leaves at a node while C. verticillata had three or more in whorls. Flowers were of different colours and were borne on stem (6), branches (5) or leaf axils (10). The fruits which were either solitary (4) or in stellate (17) forms were ellipsoid (12), long and flat (1), sub-cylindrical (2), oblong (1), sub-globose (3), boat-shaped (1) and ovoid (1). Epidermal cells were either polygonal or irregular in the species and stellate trichomes were observed in C. gigantea. Stomata were either anomocytic, paracytic or anisocytic. All taxa were hypostomatic except in C. acuminata and C. nitida. Peltate hairs were restricted to petiole of C. lepidota.Turfted and single uniseriate hairs were widely distributed while vascular bundles of the petiole were either collateral or bicollateral in the genus. Palisade cells were mostly elongated and single layered in the leaves. Pollens were generally prolate-spheroidal or sub-prolate but prolate in C. heterophylla which had a combination of triporate and dicolpate pollen grains. Alkaloids were absent in all taxa while other metabolites were either present or absent. The groupings obtained from numerical analysis showed affinity among the species in conformity to current classification of the genus. The characters observed were used to construct a key for the taxa. The classification of the genus obtained from the variability of characters of the taxa was in agreement with the current classification. An indented dichotomous key was constructed for the identification of the species.