Integrative analyses of Crepidium (Orchidaceae, Epidendroideae, Malaxideae) shed more light on its relationships with Dienia, Liparis and Malaxis and justify reinstatement of narrow endemic C. allanii

Malaxidinae are a cosmopolitan higher Epidendroid subtribe of > 1250 species that exhibit wide morphological and ecological diversity. Despite almost two centuries of taxonomic deliberation, controversy persists regarding the delimitation of practically all Malaxidinae genera, the most important of which are Crepidium, Dienia, Liparis and Malaxis. Previous attempts to classify these genera using a molecular phylogenetic approach showed Liparis and Malaxis to be polyphyletic and the floral characters traditionally used to define them as homoplastic. Emphasis has instead shifted to vegetative and ecological traits. Here, we conduct an expanded analysis of nuclear (ITS) and plastid (matK) sequences focused on terrestrial taxa, with the resulting phylogram largely corroborating the emerging picture, and we test the efficacy of four previously highlighted traits to recover the same relationships. Although growth habit is underscored as important for resolving a natural distinction between epiphytic Liparis and terrestrial 'Crepidium clade' plus 'Malaxis clade' taxa, leaf shape and venation and habitat preference are shown to be poor predictors of phylogenetic affiliation. Instead, perennating organ structure (heteroblastic or homoblastic) and placement (predominantly above- or below-ground) - are incisive, with leaf number and texture apparently correlated. These findings are discussed in the context of an inferred evolutionary history of the subtribe. Although homoplastic at the subtribe level, some floral characters are shown to be useful for resolving identities at the species level. Accordingly, the status of four long-confused species (Crepidium acuminatum, C. allanii, C. purpureum and Microstylis biloba) is resolved.

Automated summary

The study examines the classification and evolutionary history of the Malaxidinae subtribe, finding that growth habit, perennating organ structure, and placement are key factors in resolving relationships between genera, while leaf shape and habitat preference are poor predictors of phylogenetic affiliation. The findings also suggest that some floral characters can be useful for resolving identities at the species level, resolving the status of previously confused species.