A review of the taxonomy and relationships of the Dendrobium speciosum complex (Orchidaceae), and recognition of two new taxa

Abstract

Dendrobium speciosum is one of Australia's most prominent orchids. Two hundred years after the type description, there are several contrasting taxonomic treatments of the D. speciosum complex. We review the taxonomy from first descriptions and incorporate recent numerical approaches. Our explorations extend the plant range to an almost continuous distribution along the east coast of Australia, with disjunct populations along the Tropic of Capricorn. Data from field observations, and studies of 453 plants over the entire distribution range were analysed using morphological and multivariate techniques. Results indicate a species complex forming a continuum of variation. Within the continuum from north to south the varieties boreale, pedunculatum, curvicaule, capricornicum, grandiflorum, hillii and speciosum occupy geographical areas which are defined approximately, and they exhibit significant infra-varietal variation. At interfaces of described varieties, populations show intermediate characteristics. There are no distinct qualitative differences in characters between any of the varieties or groups. We describe two new varieties, var. blockdownense and var. carnarvonense from central Queensland and propose that var. capricornicum Clemesha be retained for plants of east Capricorn. © 2006 Royal Botanic Gardens and Domain Trust.