Liparis rivalis Schltr., Repert. Spec. Nov. Regni Veg. Beih. 33: 146 (1924).
Large erect terrestrial plant, up to 35 cm tall; rhizome very short; roots more or less pilose, c. 1 mm diam. Pseudobulbs slender, stem-like, up to 22 cm × 3 – 6 mm, partly covered by 4 – 8 amplectant sheaths, sometimes with a leaf-like bract just below the leaves, with 3 – 5 apical sub-petiolate leaves. Leaves asymmetric, somewhat falciform, thin, lanceolate to elliptical-lanceolate, acuminate, up to 5 – 15 – 2 – 5 cm but usually in the smaller range, pale green. Inflorescence erect, longer than the leaves, carrying up to 30 flowers, up to 15 cm. Peduncle with a few short costate peduncle sheaths sizes and several sterile bracts. Rachis densely-flowered, racemose, up to 14 × 2 cm diam. Floral bracts spreading, linear-lanceolate, acuminate, the lower ones a little longer than the pedicellate ovary, the apical ones shorter, 5.2 – 7 × 0.9 – 1.6 mm, green. Flowers small, up to 9 × 6 mm, erectly-spreading, lower ones fading before the upper ones open, ovary and column green, sepals and petals brownish-green, lip pale orange and becoming darker towards the middle to a dark orange-red on the disk; the whole becoming more yellow with age. Pedicel and ovary glabrous, costate, 4.5 – 7 × 0.5 – 1.1 mm. Dorsal sepal erect, ligulate-lanceolate, 5.5 – 7.2 × 0.3 – 1 mm. Lateral sepals porrect, forming a platform beneath the lip, narrowly oblong, 4.5 – 6.3 × 1.9 – 2.2 mm. Petals margins incurved, curved upwards, obliquely linear 5.4 – 7.0 × 0.3 – 1 mm. Lip slightly curved, broadly obovate, with very small auricles at the base, very obtuse to almost truncate at the front, the margins undulate to crenulate, with a small callus-like thickening at the base, 4.1 – 5.4 × 3.8 – 4.6 mm. Column very small 1.2 – 2.8 × 0.4 – 0.5 mm, curved at the apex, with small wings. Anther oblate with a small obtuse beak at the front, c. 0.5 × 0.5 mm. Pollinia ovoid, c. 0.3 × 0.2 mm.
Refers to the habitat, near the margin of streams, where the type specimen was found.
This is a very distinct species with a long, slender stem-like pseudobulb with asymmetric falciform leaves at the apex, and a dense rachis of small flowers. Its flowers are yellow orange with the centre of the lip dark orange to red, a broadly ovate lip, obtuse at the front and with very small auricles at the base, a scarcely visible basal callus and a very small column.
It is somewhat similar in habit to Liparis gracilipes, L. listeroides, L. puncticulata and L. danguayana but the asymmetric leaves, long inflorescence with many small flowers and very small column sets it apart. It shares with L. caulescens from Réunion a similar habit, including the somewhat asymmetric leaves, the brownish-yellow flower colour and lip shape but plants of L. caulescens are generally shorter, the spike laxly racemose (vs densely racemose), fewer flowered, the flower segments almost double the size, the lip with a distinct callus and the column larger and with angular vs rounded wings (Table 6). Some forms have slightly larger flowers than average and a lip without distinct wings but are still the same species.
Terrestrial at the edge of streams or damp places, in undergrowth in evergreen forest of gneiss and laterite. Often in deep leaf litter and moss. Altitude: 800 – 1600 m.
Flowering in December to March.
As given for the genus.
N. Madagascar. Endemic.
Flora of Madagascar: vascular plants: 49th family, Orchids / by H. Perrier de La Bathie; published under the auspices of the government of Madagascar and under the direction of H. Humbert; English revision and translation by Steven D. Beckman; Malaxideae (Orchidaceae) in Madagascar, the Mascarenes, Seychelles and Comoro Islands Kew Bulletin volume 75, Article number: 1 (2020)
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