Large epilith. Pseudobulbs narrow-conical, to 40 cm long, fleshy, erect. Leaves 2? 5, elliptic to oblong, to 25 cm long, to 8 cm wide, persistent. Flowers 20-120, to 5 cm wide, white to pale yellow, labellum with purple dots and stripes; spring. Sepals linear. Petals linear, narrower than sepals. Labellum 3-lobed, midlobe wider than long, blunt, side lobes erect, rounded.
The above description is of D. speciosum in the strict sense. Some authors regard D. speciosum as a variable species consisting of several varieties, others regard these varieties as distinct species. All these taxa are cultivated and are involved in hybridization.
D. curvicaule (F.M. Bailey) M.A. Clem. & D.L. Jones syn. D. speciosum var. curvicaule F.M. Bailey from Qld, is a robust epilith or epiphyte with cylindrical, sometimes curved pseudobulbs to 1 m long and many flowers that have short thick creamcoloured segments.
D. pedunculatum (Clemesha) D.L. Jones &M.A. Clem. syn. D. speciosum var. pedunculatum Clemesha from Qld, is a robust epilith with cylindrical pseudobulbs to 30 cm long and long-pedunculate racemes with many flowers that are smaller than those of D. speciosum.
D. rex M.A. Clem. & D.L. Jones syn. D. speciosum var. grandiflorum F.M. Bailey from Qld, is a robust epiphyte with cylindrical pseudobulbs to 90 cm long and up to 100 flowers that are very densely arranged.
D. tarberi M.A. Clem. &D.L. Jones syn. D. speciosum var. hillii F.M. Bailey from Qld & NSW, is a robust epiphyte with cylindrical pseudobulbs to 1 m long and up to 200 flowers that are smaller than those of D. speciosum.
NSW & Vic.
Source: (2005). Orchidaceae. In: . Horticultural Flora of South-eastern Australia. Volume 5. Flowering plants. Monocotyledons. The identification of garden and cultivated plants. University of New South Wales Press.