Impatiens oppositifolia

Smets, E. F. & Janssens, S. B., 2018, Balsaminaceae of Myanmar, Blumea 63 (3), pp. 199-267 : 236-237

35. Impatiens oppositifolia L. — Map 13; Plate 3a

Impatiens oppositifolia L. (1753) 937. — Type: Paul Hermann s.n (lecto, designated in Grey-Wilson (1985) BM BM000621557), Sri Lanka .

Impatiens reticulata Wall. (1830) 19; Hook.f. (1875) 448; W.J. Kress et al. (2003) 170. — Type: Coloured illustration in Wallich (1830) t. 19 (lecto, designated here), Myanmar, Rangoon.

Terrestrial, annual, glabrous herb, 20–40 cm tall. Stem erect, 2–5 mm diam, moderately branched, slightly angular, reddish green. Leaves decussate. Petiole absent– 2 mm long, c. 1.5 mm diam, green. Lamina 25–60 by 15–18 mm, ovate to elliptic to obovate, apex round to acute, base cuneate to obtuse, margin shallowly crenate, adaxial green, abaxial greyish green, glabrous, with one pair of stipular glands at the base of petiole; lateral veins 5 or 6 pairs. Inflorescence axillary, erect, 2-flowered fascicles. Flowers 13–15 by 9–12 mm, 13–15 mm deep, pink. Pedicel 22–24 mm long, c. 1 mm diam, pink. Bracts c. 2.5 by 1 mm, linear, apex acute, base cuneate, margin entire, without glands, green, persistent. Lateral sepals 2, 5–7 by 1 mm, free, falcate, apex acute, base cuneate, pink with green apex. Lower sepal 8–9 by 4–5 mm, c. 5 mm deep, navicular, apex acute and mucronate, pale pink, semi-transparent, with red reticulate veins, distal part abruptly constricted into a short hook-like spur, 5–6 mm long, red to green. Dorsal petal 5–5 by 6–7 mm, broadly ovate to broadly elliptic, cucullate, apex round to mucronate, base truncate to slightly cordate, pink, glabrous, abaxial midvein with a narrow crest terminating in a short acute point. Lateral united petals 15–17 mm long, free: the upper petals 5–6 by 1.5–2 mm, falcate, apex acute, base cuneate, pink with red lines at the base; the lower petals 11–12 by 7–8 mm, free, ovate to elliptic to obovate, apex round to slightly emarginate, midrib curved and wavy near the base, pink with dark pink near the base of midrib. Stamens: filaments 3–3.5 mm long, white; anthers pink. Ovary c. 3 mm long, c. 1 mm diam, 5-carpellate, green, glabrous. Fruits c. 10 mm long, 4–5 mm diam, fusiform, 5-lobed. Seeds c. 5, globose, c. 2 mm long, black.

Phenology — Flowering: August to January; fruiting: September to January.

Distribution — Myanmar (Kayin State, Mon State, Yangon Region), India (Madras), Thailand (western and southern).

Ecology — Growing near paddies, but not in swampy areas, 16–30 m altitude.

Other collections examined. INDIA, Johann Peter Rottler 89 (LINN- HS1379-6), Madras. – MYANMAR, Kayin State, Ruchisansakun & Thet Yu Nwe 717 (L L2071083, RAF, RANG), Hpa-An, the road to Zwegabin mountain, N16°50'12.59" E97°40'58.34", 20 Aug. 2015; Mon State, Lace 5578 (K H2015/00092 47), Amherst district (Kyaikkami), Dali reserve, alt. 100 ft (30 m), 11 Jan. 1912; Yangon Region, Parkinson 15016 (K H2015/00092 46), Rangoon district, Thayagon, 18 Sept. 1932; Wall . Cat . no. 4750 (K K001039821), Rangoon, 1826.

Notes — Impatiens oppositifolia is similar to I. chinensis but differs in having a semipellucid lower sepal with reticulate veins, and a short-hook-like spur. It is also similar to I. helferi but differs in having flowers which are 13–15 mm long vs 6–11 mm long, ovate, elliptic to oblong lamina wider than 15 mm vs linear to narrowly oblong leaf laminas which are up to 7 mm wide.

Wallich published I. reticulata without referencing any specimen. However, he included a detailed coloured illustration in the protologue ( Wallich 1830: t. 19). We decided to select that illustration as lectotype.