Impatiens helferi Hook.f.

Smets, E. F. & Janssens, S. B., 2018, Balsaminaceae of Myanmar, Blumea 63 (3), pp. 199-267 : 235-236

34. Impatiens helferi Hook.f.

Impatiens helferi Hook.f. (1905) 28; W.J. Kress et al. (2003) 169. — Type: Helfer 1215 (lecto,designated here K K000694702;isolecto P P04543314), Myanmar (Burma), Tanintharyi division, Tenasserim , 1838.

Annual herb, 20–40 cm tall. Stem erect, 2–4 mm diam, unbranched to rarely branched, glabrous. Leaves decussate. Petiole up to 1 mm long, c. 1 mm diam, glabrous. Lamina 45–65 by 4–7 mm, linear to narrowly oblong, apex acute to obtuse, base truncate to obtuse, margin slightly serrate, glabrous on both sides, with one stipular gland on each side of petiole base; lateral veins inconspicuous. Inflorescence axillary, erect, 1–3-flowered fascicle. Flowers 6–11 mm long, 5–7 mm deep. Bracts c. 1 by <1 mm, linear, apex acute, base cuneate, margin entire, without glands, glabrous, persistent. Pedicel 10–15 mm long, <1 mm diam, pilose above. Lateral sepals 2, 3.5–4 mm long, <1 mm diam, free, linear, apex acute and mucronate, base cuneate, glabrous. Lower sepal 4–5 mm long, 1.5 mm deep, navicular, apex acuminate and mucronate, glabrous, distal part abruptly constricted into a curved to incurved spur, 4–5 mm long. Dorsal petal c. 2 by 3 mm, cordate, cucullate, apex emarginate and mucronate, base cuneate, glabrous, abaxial midvein simple. Lateral united petals 8–10 mm long, free: the upper petals 2–3 by 1–1.5 mm, obovate, apex obtuse, base cuneate; the lower petals 5–6 by 3–4 mm, free, obovate, apex round, base with distinct auricle, c. 0.5 mm wide, glabrous. Stamens: filaments c. 2 mm long. Ovary c. 2 mm long, c. 1 mm diam, glabrous. Fruits 6.5–7 mm long, 2.5 mm diam, short fusiform, glabrous; fruiting pedicels 18–20 mm long, straight. Seeds 2.5 mm long, globose, black shiny; seed coat smooth.

Phenology — Unknown.

Distribution — Endemic to Myanmar (Tanintharyi division), only known from the type locality.

Ecology — Unknown.

Plate 3 a. Impatiens oppositifolia L.; b. Impatiens decurva Ruchis. & S.B.Janssens ; c. Impatiens balsamina L.; d. Impatiens curvipes Hook.f. ; e. Impatiens florulenta Hook.f. ; f. Impatiens oblongata Ruchis. & Niet ; g. Impatiens violiflora Hook.f. ; h. Impatiens allanii Hook.f. — Photos by: a–h. Saroj Ruchisansakun.

Notes — Impatiens helferi is very similar to I. chinensis but differs in having much smaller flowers. Due to these small flowers, it is also similar to I. oppositifolia but differs in having linear to narrowly oblong leaf lamina up to 7 mm wide vs ovate, elliptic, to oblong leaf lamina which is wider than 15 mm.

Hooker did not designate a holotype of I. helferi . We found two specimens collected by Helfer and named as I. helferi and we selected Helfer 1215 (K000694702) as lectotype since it has an illustration by Hooker.