CYTOMORPHOLOGICAL STUDIES OF SOME NIGERIAN ASTERACEAE (COMPOSITAE) - TRIBE EUPATORIEAE

Abstract

Cytological, seed and epidermal studies were carried out of 9 taxa belonging to 4 genera and 6 species of the tribe Eupatorieae. Chromosome counts of 2 species-Adenostemma caffrum (n=10) and A. mauritianum (n=10) are reported for the first time from the Nigerian flora and the report of Ageratum conyzoides (n=18) differed from earlier reports. The report of 2 cytotypes in Ageratum conyzoides is reported for the first time from the Nigerian flora. The pollen fertility test of all the plants studied were high and this revealed that meiosis was normal with regular bivalent pairing and the plants were stable. The achene morphology of all the taxa studied have been drawn and described for the first time. Distribution maps of all the taxa studied have been drawn and described for the first time and this revealed that the plants were of widespread occurrence in the country. The epidermal walls of all the species studied were sinuously walled and their mature stomata was anomocytic in their amphistomatic leaves except for Adenostemma perrottetii that was hypostomatic. The ontogeny of all the plants studied was agenous and this has been presented for the first time. Eglandular multicellular trichomes were present in Chromoleana odorata and Ageratum conyzoides. Contiguous stomata was observed in (Adenostemma mauritianum, A. caffrum, Ageratum conyzoides, Chromoleana odorata and stomata with only one guard cell was observed in Mikania chenopodifolia were the only stomatal abnormality found in the tribe. The stomatal size of Mikania chenopodiifolia was the highest with 46?m x 20?m x 20?m x 4?m. There was no correlation between chromosome number and habit or between achene morphology and their growth habit in the tribe. A probable pathway of the evolution of basic chromosome number in the tribe has been suggested. The results from this study has confirmed the correct placement of the genera in the tribe Eupatorieae.