Significance of morphology in the systematics of Mesembryanthemaceae : interactive database and illustrated atlas for identification

Abstract

An overview and interpretation of morphological characters is provided for the Mesembryanthemaceae. Characters useful for identification are separated from those of phylogenetic significance. A new tribal classification that relies primarily on characters of the floral nectary is proposed for subfamily Ruschioideae. Apatesieae is characterized by a broad, flat holonectary, Dorotheantheae by the broad, flat meronectary, Drosanthemeae by the lophomorphic meronectary and Ruschieae by the lophomorphic meronectary (pleisiomorphic state) and lophomorphic holonectary. Ruschieae is defined by the morphological synapomorphy: leaves basally fused. The lack of stable phylogenetic characters and extreme variation in morphological characters give the mesembs an inherent flexibility that may have predisposed this family to great adaptability, and may well have contributed to their explosive speciation in the Succulent Karoo of southern Africa. A web-based interactive key to mesemb genera was constructed. Species identification is enabled through an iterative search facility and illustrations of types. The 'Interactive Mesembs' site is available at http://www.mesembs.org. Mesembs comprise 1666 species, 4 hybrids and 112 subspecies in 126 genera. New biogeographic data showed mesembs to have extremely high levels of endemism at species level in Fynbos (93%), Albany Thicket (91 %), Succulent Karoo (89%), and Grassland (84%). At genus level, endemism is highest in Succulent Karoo (45%) and then Fynbos (24%). Most shared genera are between Succulent Karoo and Fynbos (12 genera). The most primitive extant tribe in subfamily Ruschioideae, the Apatesieae, is almost entirely confined to the southwestern Cape. Data supports the hypothesis that the Fynbos Biome is older than the Succulent Karoo Biome, and that the former biome may have acted as a mesic refuge. The number of shared genera between Fynbos and Succulent Karoo supports the recognition of the Greater Cape Mediterranean Region.