Taxonomic and Ecological Significance of Foliar Epidermal Characters in Four Taxa of Mussaenda L. (Rubiaceae) in Nigeria

Abstract

Aims: This study investigated leaf epidermal features as taxonomic markers in delimiting two West African species (M. elegans and M. erythrophylla) and two Philippine infraspecific species (M. “Doña Aurora” and M.“Doña Luz”) of Mussaenda L. in Nigeria and their ecological significance. Study Design: The experiment adopted a Completely Block Design (CBD) of four plant taxa from two study locations with 10 replicates each, totaling 80 samples. Place and Duration of Study: The study was carried out in the Department of Plant Science and Biotechnology, University of Nigeria, Nsukka, between June and September, 2010. Methodology: Fresh leaves were collected from the Tropical Rainforest (TRF) and Derived Savanna (DS) vegetations of Nigeria under the same weather conditions. Leaf epidermal strips were prepared by clearing method, stained with Safranin and observed under the light microscope. Results: The stomata are of the paracytic type borne on polygonal to irregularly shaped, wavy epidermal cells. Simple trichomes were also a common feature in all taxa. Mussaenda erythrophylla has significantly (P ˂ 0.05) the least dense stomata (84.51 ± 0.73 mm-2) while M. “Doña Aurora” has the densest stomata (230.98 ± 2.67 mm-2). M. elegans and M. “Doña Aurora” have significantly the highest stomata index (28.48% and 28.98% respectively) while M. “Doña Luz” has the lowest (24.31%). Samples from the TRF have significantly higher density, index and size of stomata in M. elegans and M. “Doña Luz” than those from DS. Quantitative trichome parameters also vary among the taxa. The fewest trichomes were observed in M. elegans (7.90 ± 0.14 and 11.75 ± 0.21) while they are most abundant in M. “Doña Luz” (11.77 ± 0.11 and 18.90 ± 0.51). Ecological conditions affected these variables as trichomes were more abundant in the specimens collected from DS locations. Conclusion: Epidermal features are proven significant tools in taxonomic delimitation and as environmental indicators in predicting climatic changes and environmental pollution.