Dendrobium parvulum Rolfe, Bull. Misc. Inform. Kew (1899) 127.
Type: Koorders 29565 (holo K, iso BO).
Small creeping mat-forming epiphyte, to 4.5 cm high. Roots 0.3.5(-1) mm diameter. Rhizome 0.2-1.3 by c. 0.1 cm, prostrate, branched. Pseudobulbs 0.2-1.5 by 0.2-0.9 cm, globose, ellipsoid or ovoid (occasionally obovoid), often obliquely placed on rhizome, dark reddish or greenish yellow, apex 2-leaved. Leaves 0.3-1.5(-2.0) by 0.2-0.8 cm, spreading, ovate to elliptic, apex acute mucronate to apiculate, green, purplish underneath; sheaths smooth, membranous, pale green sometimes flushed red. Inflorescence terminal, arising from both leafless and leafy stems (from between the leaves), 1-3-flowered (commonly 2-flowered); bracts ovate; apiculate to acuminate. Flowers 0.7-1.5 cm long, mostly widely opening, sometimes cleistogamous. Median sepal 3-8 by 1 .5-2.5 mm, ovate-oblong to oblong-lanceolate, acute to acuminate. Lateral sepals 7-14 by 2-3 mm, oblique ovate-elliptic, carinate, apiculate to acuminate; basal fused part 1-2.5 mm long, cylindrical occasionally subconical, usually somewhat swollen and large in proportion to the rest of the flower; mentum total length 4-7.5 mm, tip obtuse. Petals 3-7 by 1-2 mm, oblong-lanceolate, subacute to apiculate. Lip 5.5-12 by 1-2 mm, subtrilobate, linear-oblanceolate, adnate to column foot at base, free part usually with small central cross-ridge, apex acute to acuminate, usually reflexed. Column 2-3 mm long; foot 4-7.5 mm long; anther 1 mm broad; pollinia c. 0.5 mm long. Ovary distinctly 5-ribbed or 5-winged; pedicel and ovary 5-11 mm long. Fruit 8.5 by 4.5 mm, ovoid.
(after Reeve & Woods, 1989, as 'Dendrobium delicatulum', see note below).
Colours: Flowers red, pink-purple, violet, blue or whitish yellow, lip apex usually orange to orange-red.
Habitat: Epiphyte, growing both on tree trunks as well as smaller branches in montane forest, rarely terrestrial. Altitude 600 to 2650 m.
Flowering time in the wild: Throughout the year, but perhaps peeking from October to April. Flowers last 3-4 months, except in the autogamous form described as Dendrobium delicatulum subsp. huliorum, which has flowers lasting only about two weeks.
Distribution: Sulawesi, New Guinea, Bougainville, Solomon Islands, Caroline Islands (Ponape), Fiji, Vanuatu.
Distribution in New Guinea: Papua (Waigeo Island; Japen Island; Central Mountain range); Papua New Guinea (widespread in the mountains, but largely absent from the northern ranges).
Map: PARVUMAP.JPG [Dendrobium parvulum Rolfe (as Dendrobium delicatulum sensu T.M.Reeve & P.Woods non Kraenzl.), distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 287, map 11.]
Notes: Dendrobium parvulum is easily recognised by its mat-forming habit, 2-leaved pseudobulbs, very small, relatively broad leaves, and 5-ribbed ovary. Only Dendrobium putnamii is similar, but can be distinguished by its linear-lanceolate leaves and triangular ovary.
This species was wrongly identified as Dendrobium delicatulum Kraenzl. by Reeve & Woods (1981 & 1990). At that time they had not seen any type material of that species and had assumed this to be lost. However, a type specimen is still extant at the Hamburg herbarium, where it was examined and photographed by Mark Clements. Clements found that the true D. delicatulum is in fact very similar to, and probably conspecific with Dendrobium subacaule. Clements has kindly showed us his photograph and we are convinced that he is right. Moreover, Schlechter's illustration of D. delicatulum also undoubtedly represents D. subacaule, so we have decided to relegate D. delicatulum to the synonymy of D. subacaule. As a result, the species formerly misidentified as Dendrobium delicatulum should now be known as Dendrobium parvulum.
Reeve & Woods distinguished three subspecies in what they called Dendrobium delicatulum: D. delicatulum subsp. parvulum, D. delicatulum subsp. delicatulum and D. delicatulum subsp. huliorum. Of these the first two are distinguished only by the slightly larger flowers (12-15 mm long) of subsp. parvulum compared with subsp. delicatulum (7-12 mm). Subsp. huliorum differs from the typical subspecies in the following respects: Plant often larger, up to 4.5 cm high; pseudobulbs 5-15 by 2-9 mm, greenish yellow to yellow; leaves green on both sides; flowers 7-10 mm long, not widely opening and usually self-pollinating, sometimes cleistogamous.
We consider it preferable to recognise these subspecies only at an informal level, where they may be referred to as e.g. 'large-flowered form' and 'autogamous form'.
Cultivation: This pretty little orchid, of which the bluish violet form is a real jewel, is not easily cultivated, and probably best grown in large shallow saucers in view of its creeping habit and intolerance of drought. It does require good drainage, coolness, and fresh air.