Ontogenetic and demographic studies of Sparaxis grandiflora subspecies fimbriata (Iridaceae)

The seasonal ontogeny and phenology of Sparaxis grandiflora spp. fimbriata were examined along with various population parameters for this synanthous geophyte which possesses an annual storage organ. It was found that the majority of plants in the sample were less than seven years old with a maximum age determined at eighteen years. Age was successfully determined by examining subterranean markers (tunics) and it was found that the plants do not generally flower before they are four years old and have a ‘critical minimum corm biomass’ of 0.37 g dry matter. Corm size is related to depth of burial until reproductive maturity is reached, with over 80% of the corms found in the organic profile which extends to 3 cm below the soil surface. The seasonal allocation of dry matter to the various plant parts indicated the efficient mechanisms adopted by this species to cope with the mediterranean climatic conditions and the low soil nutrient levels.