Karyotypes in Ethiopian Aloe species (Xanthorrhoeaceae: Asphodeloideae)

Abstract

A cytogenetic survey of 17 species in the succulent-leaved genus Aloe L. (Xanthorrhoeaceae subfamily Asphodeloideae) in Ethiopia was undertaken towards a more complete genetic characterisation of the genus throughout its distribution in Africa, Arabia and Madagascar. Somatic metaphase chromosomes of all species studied showed the same diploid chromosome number of 2n = 14, consisting of four pairs of long and three pairs of short chromosomes. Symmetry was characterised as Stebbins type 2B and the asymmetry indices AsK%, TF%, A1 and A2 revealed minor karyotypic variation common in closely related species. The metrics showed that A. benishangulana has a marginally higher degree of asymmetry than is typical, and the pubescent-flowered A. trichosantha has a more symmetrical karyotype than most other species. We suggest that the stable karyotype morphology in Aloe indicates that structural genome changes and ecological factors play a more prominent role in speciation in Aloe. © 2013 The Board of Trustees of the Royal Botanic Gardens, Kew.