1 2 Vicariance, dispersal, and hybridization in a naturally fragmented system: the afro- 3 alpine endemics Carex monostachya and C. runssoroensis (Cyperaceae) 4 5 6 7 Abel Gizaw1,2, Tigist Wondimu1,2, Tusiime Felly Mugizi1,3, Catherine Aloyce Masao1,4, 8 Ahmed Abdikadir Abdi1,5, Magnus Popp1, Dorothee Ehrich6, Sileshi Nemomissa2, and 9 1 Christian Brochmann 10 11 1 12 Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway; 2Department of Plant Biology and Biodiversity Management, Addis Ababa 13 3 14 University, P.O. Box 3434, Addis Ababa, Ethiopia; School of Forestry, Environmental and 15 Geographical Sciences, Department of Forestry, Biodiversity and Tourism, Makerere University, P.O. Box 7062, Kampala, Uganda; 4Department of Forest Biology, Sokoine 16 5 17 University of Agriculture, P.O. Box 3010, Morogoro, Tanzania; Botany department, National Museums of Kenya, P.O. Box 40658-00100, Nairobi, Kenya; 6Institute for Arctic and Marine 1918 20 Biology, University of Tromsø, NO-9037, Norway 21 22 23 24 Corresponding Author: Abel Gizaw Email:
[email protected]; Natural History Museum, 25 University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway 26 1 1 2 Abstract 3 4 5 The naturally fragmented habitat on the tallest African mountains provides a good model 6 system to study vicariance, dispersal, and hybridization. Many mountains are separated by 7 lowland that likely was unsuitable for high-alpine plants even during cold climatic periods. 8 We explore the relative importance of these processes using two endemic sister species: the 9 widespread Ethiopian/eastern East African Carex monostachya and the mainly western East 10 African C.