MORPHO-ANATOMICAL STUDY OF TWO CLOSELY RELATED SPECIES OF OLDENLANDIA (RUBIACEAE) IN NIGERIA
Morpho-anatomical study of Oldenlandia corymbosa L. and Oldenlandia affinis (Roem & Schult.) DC. in the family Rubiaceae was undertaken in order to assess the taxonomic relationship of the two species. Ten samples of each of the two species were randomly collected from their natural regions of provenance, Nkalagu (derived Savanna), Nsukka (derived Savanna), and Otukpo (Southern Guinea Savanna). Both species are herbaceous and are thergefore, apomorphous than shrubs and trees, which are plesiomorphous. Comparative morphology and anatomy of the leaves, stems, roots and the flowers (pollen) of the two species were analysed. The results obtained showed great similarities and differences as well as the effect of climate on the species in their study sites. The influence of environment was not significant on O. corymbosa and O. affinis in all the morphological variables: lamina length, lamina diameter, fruit beak length, fruit stalk length, fruit length and fruit diameter in all the study sites. Leaves of both species are bifacial and hypostomatic; anomocytic and paracytic types of stomata were observed in the two species. Variations occurred among the woods of the two species which are diffuse porous with heterogenous rays; biseriate in O. corymbosa with medullary rays of 7 – cell high and uniseriate in O. affinis with medullary rays of 5 – cell high. The mean vessel length and diameter varied significantly (P ≤ 0.05) in O. corymbosa, especially in Nsukka (derived Savanna) and Otukpo (Southern Guinea savanna) in contrast to those in Nkalagu (derived savanna). In O. affinis the wood anatomical parameters varied significantly at P ≤ 0.05 in both the roots and the stems in all the study sites and insignificant in Nsukka and Otukpo in contrast to Nkalagu. This factor was supported by the vulnerability index of O. affinis which was found generally to be more vulnerable than O. corymbosa and this increased towards Otukpo which lies farther north. The variation of these anatomical parameters across species showed the strongest significant difference. Flowers of both species are complete; racemose and corymbose; petals 4 – merous and white; sepals 4 – merous; bicarpelous ovary but yellowish-white petals in O. affinis; tricolporate pollen type in O. corymbosa but tricolporate and tetracolporate in O. affinis. Therefore, judging from the array of anatomical and morphological variables of the two Oldenlandia species, they should be classified as “moderately” apomorphous.