Impatiens tirbinensis Hareesh & M.Sabu, 2020

Hareesh, Vadakkoot Sankaran & Sabu, Mamiyil, 2020, Two new balsams (Balsaminaceae) from Eastern Himalayas, India, Phytotaxa 437 (5), pp. 291-300 : 291-292

1. Impatiens tirbinensis Hareesh & M.Sabu sp. nov. ( Figs. 1 , 2 )

The new species is morphologically similar to I. drepanophora , but differs from the latter in having bract with acute apex (vs. acuminate or aristate with 2–3 mm long awn), obliquely ovate lateral sepals, apex sub-acute without awn (vs. ovate-falcate, apex aristate with 2–3 mm long up-curved awn), lower sepal with ca. 1 mm long awn, apex acute (vs. aristate with 4–5 mm long awn), lateral united petals with lorate distal lobes (vs. oblong to dolabriform) ( Table 1).

Type:— INDIA. Arunachal Pradesh: West Siang district, 5 km away from Tirbin towards Along from Daporijo, ± 787 m, N 28° 1’ 28.42’’, E 94° 36’ 29.7’’, 18 September 2019, M. Sabu & V. S. Hareesh 158721 (holotype CAL!, isotypes, CAL!, MBGH!).

Terrestrial succulent herbs, 30–45 cm long; stem rarely branched, terete, greenish brown, glabrous; internodes 3–6 cm long, dark pink at base and greenish pink towards the apex, glabrous; nodes swollen when mature. Leaves alternate at distal part and spirally arranged proximally along the stem, petiolate; lamina 4.5–12 × 2.5–5.5 cm, ovate or ovateelliptic, caudate-acuminate at apex, crenate at margin, crenations apiculate, cuneate at base, dark green above and pale green beneath, glabrous on both sides; lateral nerves 10–13 on each side of the mid-vein, abaxially prominent; petiole 1–3 cm long, slender, slightly winged, pale green, glabrous; petiolar glands subulate, pale green to pink, glabrous. Inflorescence a raceme, axillary,15–20-flowered; peduncle 6–12; bract 3–4 × 2–3 mm, navicular, acute at apex, pale green, glabrous, caducous. Flowers pale purple with yellow throat, pedicellate; pedicel 10–12 mm long at flowering and elongates up to 18 mm long in fruiting stage, pale green, glabrous; lateral sepals 2, 1.5–2 × 1–1.5 mm, obliquely-ovate, apex sub-acute, transparent with pale green midrib, glabrous; dorsal petal 6–7 × 5–6 mm, orbicular, dorsally slightly keeled middle towards the apex, apex shallowly emarginated, curved upwards, pale purple with pale green keeled portion, glabrous; lateral united petals 20.5–22.5 × 4–6 mm, 2-lobed, pale purple with yellow throat; basal lobe 4.5–5.5 × 5–6 mm, obovate to triangular, non-clawed, pale purple; distal lobe 16–17 × 1–2 mm, lorate, twisted, rounded or obtuse at apex, pale purple; dorsal auricle absent; lower sepal 18–23 long, ca. 5.5 mm wide at mouth, navicular, pale purple, glabrous; mouth with ca. 1 mm long awn, apex acute, pale green; spur 5–7 mm long, cylindrical, outwardly curved, apex entire, pale purple, glabrous. Column 4–5 × ca. 1.5 mm, slightly bent towards the apex; filaments ca. 3 × 1.5 mm, white, glabrous; anthers ca. 1 × 1 mm, yellow, glabrous. Pistil 3–3.5 × ca. 1.5 mm; ovary ellipsoid, pale green, glabrous. Capsule 15–17 × ca. 3 mm, clavate, green, glabrous; seeds ca. 2 × 1 mm, obovate, cream.

Phenology:— August to October

Etymology:— The specific epithet is named after the type locality Tirbin, West Siang district, Arunachal Pradesh.

Habitat and distribution:—The new species known only from near Tirbin, West Siang District of Arunachal Pradesh at an altitude of around 800 m a.s.l. It grows in the moist areas near the streams. At present, the new species perceive no serious threat in its habitat. We observed 8 populations with around more than 80 individuals near Tirbin, Towards Along from Daporijo ( IUCN 2001).

Figures

FIGURE 1. Impatiens tirbinensis. Habit. Photo by V.S. Hareesh.

FIGURE 2. Impatiens tirbinensis. A. Habit. B. Inflorescence (close up). C. Flower side view. D. Lateral sepal adaxial view. E & F. Dorsal petal (adaxial and abaxial view). G & H. Lateral united petals (adaxial and abaxial view). I. Lower sepal with spur. J. Column showing stamen and carpel. K. Capsule. Photos by M. Sabu & V.S. Hareesh.