Dendrobium undatialatum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1912) 542; 21 (1923) t. 183, fig. 687.
Type: Schlechter 17960 (holo B, lost; iso AMES, E, G, L, NSW).
Tufted epiphyte, 5-l0 cm high. Roots slender 0.3-0.8 mm diameter. Rhizome very short, indistinct. Pseudobulbs 1.0-3.5 by 0.3-l cm, crowded, ovoid, 2-4-noded, basal internode usually surrounded by remains of sheath fibres, apex 1- rarely 2-leaved. Leaves 1-9 by 0.6-2.7 cm, sessile, elliptic to ovate or ovate-lanceolate, usually broadest below middle, many veined, 3-5 veins prominent, base usually rounded to somewhat cuneate and slightly folded, apex acute sometimes shortly acuminate, apiculate; sheaths smooth or somewhat ribbed, with age becoming fibrous. Inflorescence terminal, c. 3.5 cm long, pedunculate, scape c. 1.5 cm long, 1-8-flowered; bracts 4-7 mm long, about half length of pedicel and ovary, ovate acuminate. Flowers 11-16 mm long, not widely spreading, Median sepal 8-10 by 2-2.5 mm, oblong to lanceolate, mid-nerve distinctly keeled, apex acute. Lateral sepals 8-15 by c. 3.5 mm, narrowly triangular, mid-nerve distinctly keeled, apex acute, apiculate; basal fused part 2.5-3 mm long, cylindrical; mentum total length 3-4 mm long, tip obtuse, bilobed. Petals 8-9 by 2.5-3 mm, oblanceolate, shortly acuminate. Lip 8-9 by 2-3 mm, subtrilobate, oblong, adnate to column foot at base, usually somewhat constricted towards middle, with (or without?) a transverse callus, margins incurved, apex not recurved, abruptly acuminate, acumen 1.5-3 mm long with a finely denticulate-ciliate basal margin. Column c. 2 mm long; foot 3-4 mm long; anther c. 1.75 mm broad; pollinia c. 1 mm long. Ovary with 6 (sometimes 5 or 7) distinctly undulate wings; pedicel and ovary 9-13 mm long. Fruit 7 by 3.5 mm, narrowly ovoid.
(after Reeve & Woods, 1989).
Colours: Flowers white, sometimes pale green, lip towards apex orange-yellow, tip white; or lip flecked orange-yellow or sometimes purple or with 5 reddish nerves; column sometimes with a yellow spot.
Habitat: Epiphyte in lower montane forest. Altitude 900 to 1300 m.
Flowering time in the wild: April-July, September.
Distribution: New Guinea, Solomon Islands.
Distribution in New Guinea: Papua New Guinea (Sandaun province: Torricelli mountains, Madang province: Finisterre mountains, Southern Highlands, Morobe and Milne Bay provinces).
Map: UNDATMAP.JPG [Dendrobium undatialatum Schltr., distribution map, redrawn from T.M. Reeve & P.J.B. Woods, Notes Roy. Bot. Gard. Edinburgh 46 (1989) 286, map 9.]
Notes: The several-flowered raceme, short mentum, ciliate lip, strongly undulate ovary-wings and one-leaved pseudobulbs together make this species quite distinct from the others of the section Pedilonum.
Examination of the flower from a living plant collected at Erave, Enga Province, showed a slight cross-ridge on the lip. This ridge is not always easy to observe and can be difficult to see in dried specimens.
Dendrobium undatialatum seems an unusually uncommon species. Its sparse and evenly scattered distribution, as presently known, over the eastern half of New Guinea to Kolombangara at the western end of the Solomon Islands may be due to its being a somewhat insignificant species and therefore perhaps easily overlooked.
Cultivation: Intermediate growing epiphyte.
(after Reeve & Woods, 1989)