Patterns of geophyte diversity and storage organ size in the winter‐rainfall region of southern Africa

Abstract

The winter‐rainfall region of southern Africa, covered largely by the fynbos and succulent karoo biomes, harbours the world's greatest concentration of geophyte species. Species diversity is greatest in the south‐west, where more than 500 species co‐occur in one quarter‐degree square; in the south‐east the values are generally around 100, and in the arid north‐west, always less than 50 (more often less than 10). In at least three species‐rich genera (Moraea, Eriospermum and Oxalis), the size of storage organs (bulbs, corms, tubers) varies inversely, with the largest average values occurring in the species‐poorer areas — both in the north‐western, and in the south‐eastern parts of the region. This negative correlation between average storage organ size and species diversity is, however, only observed at relatively large spatial scales, which suggests that there is no direct relationship between storage organ size and species diversity. More likely, both these measures are driven by winter rainfall amount and reliability, both of which peak in the south‐western Cape. We suggest that reliable winter rainfall makes large storage organs unnecessary and depresses extinction rates, thus leading to the accumulation of species.

OCBIL theory: towards an integrated understanding of the evolution, ecology and conservation of biodiversity on old, climatically buffered, infertile landscapes

“…Accentuated development of ecophysiological adaptations in roots and other underground structures is evident (Lamont 1982). Cluster roots , dauciform roots (Shane et al 2005), geophytism (Parsons andHopper 2003;Proches et al 2005a) and extensive water-foraging strategies (Poot and Lambers 2008) are evident in the Southwest Australian Floristic Region and the Greater Cape. Removal of perennial native vegetation in these regions has required massive importation of nutrients to sustain cereal agriculture (Cordell et al 2009).…”

“…Given the extensive Neogene uplift of mountains in the Greater Cape (Cowling et al 2009), the area of YODFELs is greater than in the Southwest Australian Floristic Region and Pantepui. Nevertheless, the extensive occurrence of geophytes (Proches et al 2005a) and resprouting shrubs in YODFELs occupied by fynbos, renosterveld and succulent karoo suggests that wholesale topsoil removal would be detrimental even for these landscapes so regularly disturbed by erosional and other processes.…”

Mechanical Properties of Plant Underground Storage Organs and Implications for Dietary Models of Early Hominins

“…In August 2005 and 2006, we sampled USOs from the Western and Northern Cape Provinces of South Africa, a region of celebrated geophyte diversity Procheş et al 2005Procheş et al , 2006. A majority of our data was obtained from Wayland's Farm, Darling (33°S, 18°E) and private lands outside of Kamieskroon (30°S, 18°E).…”

Spatial patterns, availability and cultural preferences for edible plants in southern Africa

“…However, it is noteworthy that the carbohydrate content of utilized geophytes (Figures , a) appears to be higher within the distribution range of this cultural group (Figures , a and b2) than in the rest of the FSA region (Figures , a and b3). The diversity of underground storage organs in the Cape flora is well‐known (Procheş, Cowling, & du Preez, ). Of the 24 species which have edible underground storage organs high in carbohydrate values, eight of them are from the Iridaceae ( Babiana curviscapa G.J.Lewis, B. dregei Baker, B. pubescens (Lam.)…”