Gastrochilus arunachalensis Nageswara Rao, (1992: 723)

Liu, Qiang, Zhou, Shi-Shun, Li, Ren, Tan, Yun-Hong, Zyaw, Myint, Xing, Xiao-Ke & Gao, Jiang-Yun, 2020, Notes on the genus Gastrochilus (Orchidaceae) in Myanmar, PhytoKeys 138, pp. 113-123 : 113

Gastrochilus arunachalensis Nageswara Rao, (1992: 723) Figure 1

Type.

INDIA. West Kameng Distinct, tropical rain forest, about 150 m a.s.l., epiphytic on tree trunks. A. N. Rao 24220 (holotype: Orchid Herbarium, Tipi!)

Description.

Epiphytic herbs. Stem, erect, 4.0 cm long and 1.0 cm in diameter, with 3-4 leaves. Leaves nearly basal, distichous, oblong, 8.0-15.0 × 1.7-2.3 cm, slightly fleshy or leathery, apex obtuse and unequally 2-lobed. 1-4 inflorescences from base of stem, sub-umbellate, often 8-10-flowered; peduncle straight, 1-2 cm, stout, with 2 cupular sheaths. Flower yellow or yellow green, with dark brown or purplish spots. Sepals similar, oblanceolate, 6.8-7.0 × 3.2-3.5 mm, base contracted, apex obtuse. Petals oblanceolate, 6.2-6.5 × 2.3-2.5 mm, apex obtuse. Lip with an epichile and a saccate hypochile; epichile triangular, 2.5-3.0 × 5.4-6.0 mm, fleshy, adaxially glabrous, with a central cushion, margin irregularly fimbriate or erose, apex rounded; hypochile cupular, ca. 6 mm tall, ca. 4 mm in diameter, white tinged with pale yellow at bottom, outside with 3 ridges. Column ca. 4 mm, stout; rostellum deeply 2-lobed; pollinia 2, ca. 1.0 mm in diam.; stipe elongate, ca. 2.0 mm; anther cap nearly subglobose, apex narrowed into a beak. Fruit cylindrical, ridged, 5-6 cm in length, 1.2-1.4 cm in diameter.

Phenology.

Flowering occurs in October and November.

Distribution and habitat.

Gastrochilus arunachalensis is previously known only from India and this is the first record from Myanmar (Putao county, Kachin state). It is epiphytic on the trunk of riparian trees in tropical rainforest in Myanmar or mixed deciduous tropical forest in India.

Additional specimens examined.

MYANMAR. Kachin State. Putao County, Wasadam village, tropical forest, 750 m a.s.l., epiphyte on the trunk of riparian trees, 14 Sep 2016, Qiang Liu 408 (HITBC!). Kachin State. Putao County, Malirun village, tropical forest, 600 m a.s.l., epiphyte on the trunk of riparian trees, 29 Nov 2017, Yun-Hong Tan M2965 (HITBC!).

Note.

Gastrochilus arunachalensis is an interesting species that was only known from the type specimen until recently, the key morphological characters of flowers being hard to interpret ( Rao 1992). Now that fresh material has been collected in north Myanmar, a detailed description of the species, including the leaf and flower colour, leaf apex shape and features of pollinia, anther cap and rostellum, are provided here. Morphologically, it is closely related to G. pechei in having the sub-triangular epichile of the lip and hypochile of the lip laterally not compressed. However, it can be easily distinguished from the latter by the small stature of the plant (leaves less than 15 cm), green or yellow green flowers, oblanceolate sepals and petals, epichile triangular without central cushion ( Kuntze 1891; Rao 1992).

Figures

Figure 1. Gastrochilus arunachalensis A habitat B front view of flower C front view of labellum and column D lateral view of labellum and column E sepals and petals; F. pollinarium G anther cap.