Cytotaxonomic studies on the West African Labiatae

The taxonomy and distribution of the West African Labiatae is reviewed. Two new genera (Homalocheilos and Neohyptis) allied to Plectranthus are described, together with seven new species (Ocimum irvinei, Plectranthus hcdlii, P. harrisii, Leocus membranaceus, Solenostemon linearifolius, S. minor and Stachys pyramidalis) and three new subspecies (Plectranthus punctatus subsp. lanatus, Solenostemon monostachyus subsp. perennis, and Leucas oligocephala subsp. tenuifolia). Also twenty-three new combinations have been made, mainly in Plectranthus and its allied genera. The status of the genus Ooleus is discussed, and it is concluded that there is no satisfactory distinction between it and Plectranthus. Accordingly, the two are combined under the latter name, though many of the species are transferred to the allied genera Leocus and Solenostemon; the limits of the latter genus being re-defined. Cytological data is of little value in distinguishing between Plectranthus and its allied genera, all the known chromosome numbers of which are summarized. Chromosome numbers are recorded for 63 of the 103 taxa of Labiatae (including introduced species) known from West Africa. In most cases these are the first published numbers for the taxa concerned. The chromosome numbers are summarized in Appendix 2. In each genus the published cytological data is briefly reviewed in relation to that now available from the West African taxa. Attention is drawn to the occurrence of cytotypes in several species–Platostoma africanum, Englerastrum graciUimum and Hyptis lanceolata each having a short euploid series, whilst aneuploidy occurs in three species of Plectranthus from Cameroon Mountain. Only in Platostoma africanum are any morphological differences, other than pollen and epidermal-cell size, apparent. The relationship between the cytological data and the taxonomy of the West African Labiatae is briefly discussed.