Impatiens trigonopteris Hook.f. ex Arisdason & Gogoi, 2017

Arisdason, Wilson & Gogoi, Rajib, 2017, Validation of Impatiens trigonopteris (Balsaminaceae), Phytotaxa 323 (3), pp. 295-298 : 295-297

Impatiens trigonopteris Hook.f. ex Arisdason & Gogoi , sp. nov. Fig. 1

Impatiens trigonopteris Hooker filius ex Burkill (1908: 190, f. 6), nom. inval.

Type:— INDIA: West Bengal, Darjeeling, Jorpokri & under Simana, 6000–8000 ft, 3rd October 1906, I. H. Burkill 27760 (Holotype, K 000694751, image!). Fig. 2

Diagnosis:—Annual, succulent with fibrous roots. Stems terete, sparsely branched, to 40 cm high, without swollen nodes. Leaves alternate, exstipulate, mainly confined to the upper parts; petioles 0.5–1.5 cm long; blade elliptic, 1.5–8.5 cm long, glabrous, base cuneate to slightly attenuate, margins crenate or crenate-dentate, apex acuminate; lateral veins to 12 pairs, subopposite. Inflorescence axillary, erect, racemose, to 10.3 cm long, to 18-flowered; peduncles to 3 cm long; pedicels to 1 cm long; bracts basal, lanceolate, 3–4 mm long, apex acuminate, persistent. Lateral sepals 2, falcate, to 2.5 mm long with a prominent awn at apex. Lower sepal navicular, yellow, abruptly tapering into a spur, 1–1.5 cm long including the spur; mouth to 6 mm wide, apex awned; spur straight, to 8 mm long. Dorsal petal hood-like or navicular, c. 2 × 3 mm, dorsally non-cucullate. Lateral united petals yellow, 2-lobed, totally unequal in size, to 0.9 cm long (whole); basal lobe obovate, c. 2 × 2 mm, apex obtuse or rounded; distal lobe unevenly triangular, to 9 × 4.5 mm, obliquely truncate with apex acuminate. Stamens 5, encircling the ovary. Capsules club-shaped, to 1.5 cm long; immature fruits somewhat ellipsoid with a groove in middle.

Flowering & Fruiting:—September–October.

Habitat:—Wet ridges, at elevations ranging from 1830 to 2450 m.

Distribution:— India (Eastern Himalayas, Darjeeling, West Bengal). Endemic.

Affinities:— Impatiens trigonopteris closely resembles I. racemosa DC. and I. reticalcarata S. Akiyama by having a racemose inflorescence and navicular flowers but differs from them by the lower sepal being abruptly tapering into a straight spur and the distal lobe obliquely truncate.

Etymology:—The specific epithet, ‘ trigonopteris ’ refers to the triangular shape of the distal lobe of the lateral united petals.

Note:—This species apparently has never been collected after its type collection. Vivekananthan et al. (1997), who contributed the taxonomic account of the family Balsaminaceae for Flora of India, included it on the basis of Burkill (l.c.), but they did not mention the source of the provided description. It is assumed here that the description they provided was probably based on Kew’s cibachrome of the only existing [holotype] specimen. Ghara (1997) reported the distributions of 32 species of Impatiens in West Bengal, but he did not include I. trigonopteris .

Furthermore, there is neither a report nor a collection of this species by the recent workers either from the adjacent Sikkim Himalayan region ( Chakrabarty 2009) or Bhutan ( Grey-Wilson 1991). The recent report on the rediscovery of this species from Sikkim Himalayas by Sumanth et al. (2017) requires authentication of species identity, as the photographs of the live plant and herbarium specimen provided in the paper look different from each other. Therefore, intensive explorations in the type locality and localities with similar habitats in the Himalayan tracts of West Bengal and Sikkim are prerequisite to determine the exact range of geographic distribution and numbers and sizes of populations of this unique Impatiens species.

Figures

FIGURE 1. Impatiens trigonopteris: A. Habit. B. Lateral view of flower. C. Bract. D. Lateral sepal. E. Lower sepal. F. Dorsal petal. G. Lateral united petal. H. Stamen. I. Immature capsule [Illustration drawn from I.H. Burkill 27760, by D.K. Sah].

FIGURE 2. Holotype of Impatiens trigonopteris (I.H. Burkill 27760, K000694751). Reproduced with permission from the Board of Trustees, Royal Botanic Gardens, Kew.