The Gerire Hills, a SE Ethiopian outpost of the transitional semi-evergreen bushland: vegetation, endemism and three new species, Croton elkerensis (Euphorbiaceae), Gnidia elkerensis (Thymelaeaceae), and Plectranthus spananthus (Lamiaceae)

摘要

The vegetation of the plateaux of the Gerire Hills, of unique geology, represents an outlier of the Transitional semi-evergreen bushland of the eastern escarpment of the Ethiopian highlands, about 160 km from continuously distributed vegetation of this type. In the lowland surrounding the hills is deciduous Acacia-Commiphora bushland, typical of the Somalia-Masai region. Unpublished data from a 1937 Italian expedition documents past existence of Juniperus procera on the plateaux. Three new narrowly endemic species are described here from recently collected material: Croton elkerensis Friis & M.G. Gilbert (Euphorbiaceae), Gnidia elkerensis Friis & Sebsebe (Thymelaeaceae), and Plectranthus spananthus A.J. Paton, Friis & Sebsebe (Lamiaceae). Three previously described species from the hills, Blepharispermum obovatum Chiov. (Asteraceae), Aloe elkerriana Dioli & T.A.McCoy (Aloaceae) and Euphorbia bertemariae Bisseret & Dioli (Euphorbiaceae), are narrow endemics. The species most similar to the bushlandendemics occur in a range of vegetation types and phytochoria in East Africa south of Ethiopia or more widespread in Africa. The species most similar to the succulent endemics occur elsewhere in semi-evergreen bushland on limestone at the mountain rangein northern Somalia. The Gerire Hills endemics are considered Vulnerable (VU) or Least Concern (LC) given the differing threats to their respective habitats.