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)

ABSTRACT

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 Unpublished data from a 1937 Italian expedition documents past existence of Juniperus procera on the plateaux.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 bushland endemics 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 range in northern Somalia. The Gerire Hills endemics are considered Vulnerable (VU) or Least Concern (LC) given the differing threats to their respective habitats.

KEYWORDS:

• Acacia-Commiphora bushland
• Audo Range
• conservation
• gravitational spreading domain
• Somalia-Masai region
• taxonomy
• Yesomma sandstone

Acknowledgements

On our field trips to the Gerire Hills in 2014 and 2016 we used a 4WD vehicle, kindly lent us by the Addis Ababa University. We thank our travel companions, Wege Abebe (Addis Ababa University), Abubaker Adem (our guide from Bale), and Ermias Getachew (Addis Ababa University). Melaku Wondafrash, Shewangziwe Lemma, Wege Abebe, Shambel Alemu, Ermias Getachew and Elias Tadesse, all staff members at the Ethiopian National Herbarium and the Addis Ababa University, kindly went on a collecting trip to the Gerire Hills in 2016, collecting and photographing the new species. We thank Daniel Mège for his kind checking our text regarding topography, geomorphology and geology. We thank Riccardo M. Baldini and Lia Pignotti at the Centro Studi Erbario Tropicale, Universitá degli Studi, Firenze, for help with scanning the manuscript report at FT, Cenni monografici sul paese dei Gherire. Last, but not least, we are obliged to Victoria Gordon Friis, Copenhagen, for her excellent work with the three drawings of the new species.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Carlsbergfondet [2013_01_0051; CF14-0047; CF15-0074; CF16-0040].