An introduction to Caladenia R.Br. - Australasia's jewel among terrestrial orchids

Caladenia is a genus of more than 250 species of geophytic orchids in the Tribe Diurideae endemic to the Australasian Region. The genus in this broad sense has an exceptional diversity of insect pollination adaptations among its colourfully adorned species, from food-rewarding generalists to specialists achieving pollination by sexual deception of male thynnid wasps. The exploration of diversity in Caladenia involves many of the great names in the foundation of Australasian plant systematics, as well as reflecting a remarkable second phase of discovery and description over the past three decades. Molecular phylogenetics has greatly clarified relationships of Caladenia and established six major clades within the genus. Some researchers regard these clades as genera themselves, whereas they are treated as subgenera herein to maximise nomenclatural stability and information retrieval. More work is needed to adequately document relationships within each of these clades, and disputed matters of typification greatly influence nomenclature applied to many species if the six clades are recognised as genera. Given the relatively recent and ongoing discovery of so many new species in Caladenia, the biology of these orchids is only now being documented comprehensively. Significant advances in pollination ecology, mycorrhizal studies, horticulture and conservation biology are emerging that highlight the extraordinary ecological sensitivity and conservation vulnerability of the genus. Indeed, the high species number and complex biotic connections have resulted in no other genus of terrestrial orchids possessing such a large number of rare and threatened taxa. Some of this rich body of new data is presented by a diverse range of laboratories and researchers in this special issue.