Taxonomic Relationships in the Aloe Morijensis (Xanthorrhoeaceae) Complex
Uleh, Amodu Mark
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Cutler and his colleagues (1980) investigated evolutionary relationships in the tetraploid shrubby species of Aloe in Kenya. They concluded that the tetraploid shrubby species, Aloe kedongensis and Aloe nyeriensis had evolved from a form very close to the diploid Aloe morijensis S. Carter & Brandham in which chromosome doubling had occurred, followed by spreading northwards from Morijo in Narok County. However, in contrast to the tetraploid shrubby species that have aloitic cells which produces exudates, A. morijensis has fibres in the leaves in place of the aloitic cells that produce distinctive exudates in most aloes. A return to aloitic cells from fibres would be a reverse of an evolutionary trend, which is unlikely in science. Hence, this conjectured origin of the shrubby species and their relationship with A. morijensis was investigated, vis-a-vis the tetraploid shrubby A. nyeriensis Christian and A. kedongensis Reynolds, using anatomical characters not employed by Cutler et al. The presence of lignified cells was seen in the base, middle and apex of the lamina of A. morijensis while in the case of the tetraploid shrubby species only aloitic cells were found. These results suggest that it is very unlikely that A. morijensis is the ancestor of the tetraploid shrubby aloes. Also, Aloe morijensis has been found at several localities in Kenya in addition to the type locality near Morijo, and also in Tanzania, but there appear to be some differences between the populations. Population variation was investigated by considering morphological, anatomical and phytochemical characters. The Kruskal- Wallis Test was used to analyze data generated for phytochemistry while the morphological characters were coded into numerical values and a dendrogram drawn using Minitab software to show relationships among the fibrous species. Results suggest that the Eastern variant of A. morijensis should be recognized as a distinct variety. The chromosome number of A. tegetiformis L.E. Newton was not determined by the nomenclatural author. In view of its location further north than the tetraploid shrubby species, its relationship with A. morijensis was also investigated. Results confirm that A. tegetiformis is a species distinct from A. morijensis.