Dendrobium speciosum (Dendrocoryne: Orchidaceae) complex in north Queensland

Dendrobium speciosum Sm. has received insufficient taxonomic study north of St Lawrence, Queensland, where plants display much morphological variation in diverse habitats. Two varieties have been described previously, variety pedunculatum, occurring north of Townsville, and variety curvicaule for plants between the Connors Range south of Mackay and Annan River, south of Cooktown. In this multivariate analysis of 107 representative plants sampled from areas between St Lawrence and Cooktown, cluster analysis and principal coordinates analysis, were used to categorise the variation. Three overlapping varieties are revealed. North of Townsville variety pedunculatum intergrades with a medium-to-tall rainforest form, which separates with a small overlap in analyses from variety curvicaule plants south of Townsville. We formally describe these rainforest forms, previously referred to as variety curvicaule, as a new variety, Dendrobium speciosum variety boreale, which occurs between Cooktown and Mt Elliot, south of Townsville. Variety boreale is characterised by the presence of a collum in most individuals, medium to long pseudobulbs, large, wide leaves, long pedicels, and fairly uniform off-white to cream flowers. Dendrobium speciosum variety curvicaule Bailey is shown to be a name of uncertain application, and is neotypified to apply to the southern group of north Queensland plants, which occur between St Lawrence and Mt Dryander and on the Whitsunday Islands. Variety curvicaule is characterised by pseudobulbs that are of medium length, wide base and have an inconspicuous collum. The flowers have relatively wide segments in relation to all other varieties, long wide petals and incurving lateral sepals.