ORCHIDACEAE
Arachnis Blume, Bijdr. Fl. Ned. Ind.: 365 (1825).
Esmeralda Rchb.f.
By: Bhakta B. Raskoti
Taxon Description
Epiphytic, monopodial herbs. Rhizome stout, roots aerial, emerging from leaf sheaths along stem. Stem scandent, terete, stout, nodded. Leaves distichous, leathery, base sheathing, apex unequally 2-lobed. Inflorescence axillary, racemose, laxly flowered; floral bracts persistent. Flowers widely opening. Sepals and petals similar, free, spreading, overlapping. Petals similar to sepals, smaller in size. Lip 3-lobed; lateral lobes erect; mid-lobe reniform, clawed, margin crenate; disk with longitudinal ridges and 2 callii. Column stout, winged, foot absent; anther cap terminal; pollinia 4 in 2 pairs, subglobose, attached by a triangular stipe to a viscidium. Fruit a capsule.
Taxon Statistics
Worldwide 16 species distributed in E Asia, Himalayas, Assam-Burma and SE Asia. 2 species in Nepal.
Key to Species
1a Dorsal sepal elliptic. Lip epichile ovate, disk with 3–5 ridges……….1. A. cathcartii
b Doral sepal oblong. Lip epichile reniform, disk with 7–9 ridges……….2. A. clarkei
1. Arachnis cathcartii (Lindl.) J.J.Sm., Natuurk. Tijdschr. Ned.-Indië 72: 75 (1912).
Vanda cathcartii Lindl., Fol. Orchid. 4: 8 (1853); Arachnanthe cathcartii (Lindl.) Benth. & Hook.f; Esmeralda cathcartii (Lindl.) Rchb.f.
Plants 35–55 cm tall. Roots aerial, fibrous. Stem stout, nodded, branched, enclosed within leaf sheaths. Leaves oblong, 11–15 × 1.7–3 cm, apex obtuse, unequally bilobed. Inflorescence lateral, 5–13 cm. Peduncle 3–5 cm, with 2 or 3 sheaths; rachis 4–5 cm, slightly zigzag, 2– or 3-flowered. Peduncle bracts 15–20 × 6–8 mm, apex obtuse. Floral bracts broadly ovate, 15–20 × 8–15 mm, apex obtuse. Flowers pale yellow with transversely reddish brown stripes, 5–6 cm across. Pedicel and ovary 2–3 cm. Dorsal sepal oblong, 25–35 × 7–9 mm, apex obtuse. Lateral sepals falcately oblong, 22–30 × 8–9 mm, apex obtuse. Petals falcately oblong-sphatulate, 24–30 × 5–8 mm, apex obtuse. Lip 15–16 × 8–9 mm; hypochile ca. 5–6 × 4–5 mm, with 2 auriculate lateral lobes; mesochile 4 × 2–3 mm; epichile reniform, 6–9 × 9–13 mm, margin crenulate; disk with 7–9 ridges and 2 calli. Column 10–14 mm. Capsule ellipsoid-cylindric, 6–7 × 1.5–2 cm.
Distribution: Nepal, E Himalaya and Assam-Burma.
Altitudinal range: 600–2000 m.
Ecology: Epiphytic on tree trunks in shady forests.
Flowering: March– April. Fruiting: June–October.
2. Arachnis clarkei (Rchb.f.) Sm., Natuurk. Tijdschr. Ned.-Indië 72: 76 (1912).
Esmeralda clarkei Rchb.f., Gard. Chron., n.s., 26: 552 (1886); Arachnanthe clarkei (Rchb.f.) Rolfe; Vanda clarkei (Rchb.f.) N.E. Br.
Plants upt to 1 m tall. Roots aerial, fibrous. Stem stout, nodded, branched, enclosed within leaf sheaths. Leaves oblong, 10–15 × 1.7–3 cm, apex obtuse, unequally bilobed. Inflorescence lateral, 5–13 cm. Peduncle 3–5 cm, with 2 or 3 sheaths; rachis 4–5 cm, slightly zigzag, 2– or 3-flowered. Peduncle bracts 15–20 × 6–8 mm, apex obtuse. Floral bracts broadly ovate, 15–25 × 8-–15 mm, apex obtuse. Flowers pale yellow with transversely reddish brown stripes, 5–7 cm across. Pedicel and ovary 2–3 cm. Dorsal sepal oblong, 30–40 × 7–9 mm, apex obtuse. Lateral sepals falcately oblong, 25–30 × 8–9 mm, apex obtuse. Petals falcately oblong-sphatulate, 22–35 × 5–7 mm, apex obtuse. Lip 13–18 × 8–10 mm; hypochile ca. 5–6 × 4–5 mm, with 2 auriculate lobes; mesochile 4 × 2–3 mm; epichile reniform, 6–9 × 9–13 mm, margin crenulate; disk with 7–9 ridges and 2 calli. Column 9–14 mm. Capsule ellipsoid-cylindric, 6–7 × 1.5–2 cm.
Distribution: Nepal, E Himalaya, Assam-Burma, E Asia and SE Asia.
Altitudinal range: 500–2100 m.
Ecology: Epiphytic on tree trunks or lithophytic on rocks in shady areas.
Flowering: October. Fruiting: November–January.