Agrostis kilimandscharica (Gramineae) and Its Allies in Eastern Africa

Abstract

While preparing an account of the genus Agrostis for the 'Flora of Ethiopia', I discovered several anomalous specimens from the Ethiopian highlands, either undetermined specifically or referred provisionally to the East African species A. kilimandscharica Mez and the West African species A. mannii (Hook.f.) Stapf. A preliminary investigation of these 2 species showed them to be extremely variable, not only vegetatively (probably at least partially in response to environmental factors), but also in spikelet characteristics, with the specific boundaries far from well defined. In order to determine the correct identity of the Ethiopian collections, it was therefore necessary to undertake a detailed study of variation within this group of Agrostis. A. kilimandscharica and A. mannii are extremely closely related, and are referred to in the 'Flora of Tropical East Africa' as being only 'barely distinct'. A third species, A. producta Pilg. from East Africa, also falls within this group, the three species forming a closely knit species-complex. The group as a whole is characterized by the possession of a loosely tufted habit, linear flat leaves, loose flexuous panicle, and spikelets with a sub-basally awned, hairy lemma. All three species are upland plants, occurring only on mountains over 2000 m. A. mannii is mainly confined to the highlands of West Africa (Cameroon and Fernando Po), but the centre of distribution and variation for this group is the highlands of East Africa. Only A. producta extends southwards beyond the mountains of northern Tanzania, occurring on the high ground of Mbeya and in Malawi. These are grasses of the montane forest belt, and the grass and scrubland above to about 3500 m. A. kilimandscharica is particularly frequent in clearings in bamboo forest and in ericaceous scrubland, and only on Mt Kenya does it penetrate upwards into the lower levels of the alpine moorland belt (above 3500 m). At the lower extreme, A. kilimandscharica also occurs in central Kenya below the present level of the montane forest in the area extending from Mt Kenya and the Aberdares towards the Cherangani Hills and Mt Elgon. However, Hedberg (Biol. J. Linn. Soc. 1: 140 (1969)) has shown that these areas linking the higher ground in Kenya are climatically suited to montane forest, which indeed once covered this area, but has been progressively cleared by man for agriculture. Presumably populations of A. kilimandscharica from these areas have been able to persist in the secondary habitats which have arisen since the montane forest was cleared.