Constraints to symbiotic germination of terrestrial orchid seed in a mediterranean bushland.

•  The dependence of seeds of terrestrial orchids on specific fungi for germination provides a means of locating these fungi in the wild and to investigate the role of appropriate fungi in the germination of orchid seed and development of seedlings under natural field conditions. •  Seed baits, comprising orchid (Caladenia arenicola) seed enclosed in fine nylon mesh, were placed at sample points along four transects through two orchid populations in bushland in Western Australia. Seed germination was scored and compared with adult orchid plant distribution and soil factors. •  A small fraction of available seed (< 1%) germinated to a stage of tuber formation where survival over the subsequent dry season would have been possible. Germination increased in the vicinity of adult C. arenicola plants, but other factors, such as soil potassium levels and presence of leaf litter, were also correlated with seed germination. •  The measurement of the spatial variability in germination events within an orchid habitat demonstrated the availability of new recruitment sites. This information is required to assess the natural recruitment capacity and the potential for orchid reintroduction in natural habitats.