AFRICAN

ORCHIDS

Orestias stelidostachya (Rchb.f.) Summerh., Bull. Misc. Inform. Kew 1937: 460 (1937).
Homotypic Synonyms:
Microstylis stelidostachya Rchb.f., Otia Bot. Hamburg.: 118 (1881).
Malaxis stelidostachya (Rchb.f.) Kuntze, Revis. Gen. Pl. 2: 673 (1891).
Description:
Plants (10 -) 15 - 25 (- 28) cm tall, few to many compactly clustered. Rhizome few mm long between shoots, 1.8 - 3.6 mm Ø, sometimes branched, node scales loose. Leafy stem (4 -) 6 - 10 (- 12) cm long, (0.13 -) 0.2 - 0.26 (- 0.3) cm Ø; basal scales 1.6 - 2.8 cm long, 0.2 - 0.55 cm 0. Leaves (2 -) 3 (- 4); leaf petiole (0.2 -) 0.4 - 0.8 (- 1.4) cm long, (0.3 -) 0.4 - 0.5 (- 0.65) cm wide when spread; leaf sheath (0.6 -) 1 - 2 (- 2.8) cm long, (0.15 -) 0.3 - 0.4 (- 0.5) cm Ø, green, sometimes fawn tinged; leaf blade (2.8 -) 5.5 - 6.5 (- 7) cm long, (2.4 -) 3 - 4 (- 5) cm wide, broadly ovate, ovate to oblong ovate, apiculate at apex, green above, paler beneath. Inflorescence (6 -) 9 - 16 cm long; raceme (3 -) 4 - 8 (- 10) cm tall, 10 - 40-flowered; peduncle (3 -) 5 - 6 (- 7) cm long. Sterile bracts about 3-6,4.6 - 6.5 mm long, 1.8 - 2.6 mm wide. Floral bracts 1.8 - 4.5 mm long, 0.8 - 1.7 mm wide. Ovary 1.5 - 3.6 mm long, 0.4 - 0.65 mm 0; pedicel 2-3 mm long, 0.3 - 0.5 mm 0; sinuate, green. Flowers (5.6 -) 6 - 7.2 mm 0; white and green tinged with red or brown, to purple-red (particularly lip with intensively coloured spot). Dorsal sepal 3.8 - 4.2 mm long, (1.8 -) 2 - 2.6 mm wide, erect, oblong ovate to oblong. Lateral sepals 2.8 - 3.2 mm long, (1.8 -) 2 - 2.4 mm wide. Petals (3.3 -) 3.5 - 4 mm long, (1.2 -) 1.4 - 1.5 mm wide. Lip 2.7 - 3.3 mm long, 2.4 - 3 mm wide, longer than broader and than lateral sepals length; lamina peariform in outline; basal auricles often with involute edges; the middle part of lamina broadly depressed, just below the lip base with characteristic convexities - 2 pubescent, symmetrical cushions - each of them reniform, with dark and intensively coloured spot; lamina at distal margins deeply cleft, each sublobe obliquely truncate, with minute apiculate apex between them. Gynostemium 1.2 - 1.8 mm long; column 0.4 - 0.6 mm wide at base; rostellum 0.75 - 0.9 mm long, 0.25 - 0.32 mm wide, transversely flabellate to fishfinlike with gently indentation at the middle of distal margin, basal edge narrowly incurved; stigma in widely opened, narrow, deep pocket; anther 0.25 - 0.3 mm long, 0.32 - 0.4 mm wide, 0.25 - 0.3 mm high, trapezoid, the distal edge shorter; loculi distinctly separated from each other. Fruit 5.8 - 7.8 mm long, 3.5 - 5.6 mm Ø.
Habitat:
Terrestrial; in leaflitter; in primary humid lowlands forest, amongst minute mosses; in primary, dense humid, mountain forest; sometimes between Cyperus papyrus; also found in secondary forest on ancient plantations. Alt.: 200 - 1550m.
Note:
Similarly to O. elegans flowers colour probably depends on intensity of light at locality. Flowers of plants growing in lighter places were darker and more intensively coloured.

Amongst all species of the genus O. stelidostachya is characterized by the largest lip, longer than wide, peariform in outline, with deep and distinct cleft at distal margin. Pubescent convexities of lip are placed near its base (weakly reaching out of ends of lip lateral auricles), lip usually completely covering the lateral sepals, as well.
Distribution:
São Tomé
References:
Exell A.W., 1944: Catalogue of the vascular plants of S. Tome (with Principe and Annobon): 320-321. - London: British Museum.
Summerhayes 1937: Africa Orchid, 9. - Kew Bull. 1937: 457-466.
Summerhayes 1956: - In Troupin, FI. Spermolt. Parc Nat. Garamba (Explor. Parc Nat. Garamba Miss. H. de Saeger, Fasc. 4.) 1. Gymnosp. & Monocot.: 258.
Szlachetko D.L, Margonska H.B., Kras M & Kowalkowska A., 2006 (in press): Contribution to the Orchid flora of West Central Africa. Vol. 2. - Krakow. Institut of Botany, Polish Academy of Sciences.
Szlachetko & Olszewski (2001). Orchidaceae. - In: Morat P. (ed.): Flore du Cameroun 2. 36: 322-670 + 130 maps. - Paris: Museum National d’Histoire naturelle & Yaounde: Herbier National.
Images:
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