Stereochilus arunachalensis Chowlu & A.N.Rao, 2020

Chowlu, Krishna & Rao, A. Nageswara, 2020, Stereochilus arunachalensis, a new orchid species of Orchidaceae (Epidendroideae: Vandeae: Aeridinae) from Arunachal Pradesh, India, Phytotaxa 433 (2), pp. 177-180 : 177

Stereochilus arunachalensis Chowlu & A.N.Rao , sp. nov. ( Figs. 1 , 2 )

Type:— INDIA. Arunachal Pradesh: Lower Dibang Valley District, Hunli , 04 June 2018, Chowlu 41000 (holotype ARUN) .

Stereochilus arunachalensis is similar to Stereochilus erinaceus ( Reichenbach 1864: 298) Garay, (1972: 205) in having the midlobe of lip embracing the lateral lobes in lower half but differs in having the sepals glabrous outside, long narrow subterete leaves and a solitary-flowered inflorescence instead of sepals glandular hairy, short broad leaves and many-flowered inflorescence. It is also allied to another locally occurring species viz. Stereochilus hirtus Lindley (1858: 38) in having a pubescent rachis and ovary but can easily be distinguished from the latter by petals that are adherent to dorsal sepal to form a hood over the column.

Epiphytic herb. Roots 1.0‒ 1.5 mm thick, long and firmly attached to the tree trunk. Stem 2‒5 cm, purplish green. Leaves 3.‒7.0 × 0.3‒0.5 cm, linear, subterete, obtuse, green spotted with purple towards base. Inflorescence axillary, solitary flowered, floral bracts triangular, acute, purple, strongly adherent to the pedicellate ovary. Flower solitary, c. 1.0 cm in diameter, brownish yellow with white lip tinged purple, pedicel and ovary c. 1.1 cm long, glandular pubescent, green tinged with purple. Sepals glabrous, dorsal sepal 4.0‒6.0 × 2.5‒3.0 mm, erect, obovate-oblong, apiculate, lateral sepals 5.0‒7.0 × 2.4‒2.8 mm, spreading, oblong-elliptic, apiculate. Petals 3.5‒5.5 × 2.5‒3.0 mm, obovate-oblong, obtuse, minutely crenate at margins, pale pink suffused with yellow basally, adherent to dorsal sepal to form a hood over column. Lip situated at right angle to column, trilobed, lateral lobes transversely rectangular, c. 2 mm long, with pointed tips, white with pinkish bar along upper margins, midlobe 4–5 mm long, ovate, subacute, white, gently undulate at margins, embracing the lateral lobes in lower half; spur 3‒4 mm long, conico-tubular, yellow; back wall of callus oblong, dorsally grooved from column base to spur mouth and gradually extended down to spur apex as a ridge; front wall callus oblong, placed at spur mouth. Colunm 4‒5 mm long, greenish yellow and white towards apex, with horizontal long acuminate rostellum. Anther cap 0.5‒1.5 mm long, white with purple tinge, 2 chambered at base and gradually drawn into acuminate tip. Pollinia 4 in 2 pairs, ovoid, yellow, attached to stipe by short, distinct caudicles, stipe spathulate, viscidium lanceolate.

Flowering:— June

Habitat and ecology:— Small epiphyte found growing on lichen and moss covered tree trunks and branches in wet evergreen subtropical forest at an elevation of 1000 m. The species is presently restricted to its type locality Hunli in Lower Dibang Valley district of Arunachal Pradesh.

Etymology:— Named for the state Arunachal Pradesh, India , where it was collected.

Conservation Status:— Known thus far only from the type locality in small population comprising of about 40 plants with an area occupancy of 4 km 2.

Figures

FIGURE 1. A. Plant in its natural habitat. B. Flower, front view. C. Flower, side view. D. Sepals and petals. E. Column with ovary. F. Lip with spur. G. Lip with spur, longitudinal section. H.Anther cap with pollinarium. (Photograph by K. Chowlu.)

FIGURE 2. A. Plant. B. Flower, front view. C. Sepals and petals. D. Lip. E. Longitudinal section of lip and spur. F. Column and ovary. G. Anther cap. H. Pollinarium. (Drawn by K. Chowlu.)