The Eriochilus dilatatus (Orchidaceae) complex in Western Australia: Subspecies taxonomy is not supported by consistent differences in morphology or distribution

A detailed study of taxonomic features of the Eriochilus dilatatus (Orchidaceae) complex (white bunny orchids) in Western Australia found that there were no consistent differences among most subspecies when herbarium specimens or living plants were compared. These subspecies were originally segregated primarily by differences in leaf size and shape and the number of flowers produced, but a critical examination of herbarium specimens found that these features were highly inconsistent within taxa. These features were also found to be highly variable over time and space within populations of living plants. The distribution patterns, habitat preferences and flowering times of these taxa were found to overlap, even for subspecies brevifolius and orientalis, which occupy the northern and eastern limits of the distribution of this species. Eriochilus dilatatus subsp. magnus and subsp. multiflorus were shown to be synonyms of subsp. dilatatus, whereas subsp. undulatus and subsp. orientalis are synonymised under subsp. brevifolius. As a result of this study, the two recognised subspecies are subsp. dilatatus and subsp. brevifolius, which can be readily separated by plant height, flower numbers and leaf morphology, except for a few intermediate plants where ranges overlap. New keys and descriptions to these taxa are provided. The reasons for previous taxonomic confusion in this group and in many other Western Australian orchids are discussed and research approaches to resolve these issues are suggested.