Impatiens oblongata Ruchis. & Van der Niet, 2018

Ruchisansakun, Saroj, Suksathan, Piyakaset, Niet, Timotheüs Van Der, Smets, Erik F. & Janssens, Steven B., 2018, Three new species of Impatiens (Balsaminaceae) from Myanmar, Phytotaxa 338 (1), pp. 63-74 : 70-71

3. Impatiens oblongata Ruchis. & Van der Niet , sp. nov. ( Figs. 6 , 7 )

Impatiens oblongata Ruchis. & Van der Niet is most similar to I. patula Craib (1926: 164) but can be distinguished by a distinctly shorter spur, broadly oblong upper lateral united petals with a truncate to slightly emarginated apex, and the apex of the lower lateral united petals truncate to slightly bilobed.

Type:— MYANMAR. Shan State: Kalaw, 20°39’24”N, 96°34’96”E, 1569 m elevation, 27 Sep. 2015, S. Ruchisansakun & Makino BG Exped. 735 (holotype L 2071128!, isotypes L 2071129, L 2071130, L 2071131!, RAF!, RANG!).

Terrestrial annual herb 30–50 cm tall. Stem erect, 1–4 mm in diam., angular, simple, or moderately to richly branched, red, mostly glabrous except sparsely pilose towards apex. Leaves spirally arranged. Petiole 3–10 mm long, ca. 1 mm in diam., pale green to pink, pilose. Lamina 50–75 × 10–20 mm, lanceolate to narrowly ovate, apex acute, base cuneate to attenuate, margin serrate, adaxial green, abaxial pale green, pilose on both sides, with 3–5 long red hairs along the margin near base; lateral veins 6–7 pairs. Flowers solitary, axillary, erect, 19–20 × 16–18 mm, 14–17 mm deep, pink, with two small dark pink dots and two small yellow dots at center. Bracts ca. 2 mm × <1 mm, linear, apex acute, base cuneate, green with red apex, pilose, persistent. Pedicel 18–20 mm long, less 1 mm in diam., pink, pilose. Lateral sepals 2-4: upper pair ca. 2 × <1 mm, sometimes absent, linear to oblong, apex acute, base cuneate, pale green with red tip, pilose; lower pair 1.5–2 mm × 1.5–2 mm, ovate, apex acuminate, base obtuse, pink, glabrous. Lower sepal 5–6 × 3–4 mm, 3–4 mm deep, navicular, apex acuminate and mucronate, pale pink with dark pink mark near base, pilose outside, distal part abruptly constricted into a straight or curved spur, 8–12 mm long, pink with dark pink tip. Dorsal petal 5–6 × 6–9 mm, broadly obovate, flat, apex truncate and stipitate, to 2 mm long, base truncate, pink with green stipitate tip, glabrous with pilose midrib and tip, abaxial midvein with an acute appendage, <1 mm tall, pink or green. Lateral united petals 12–14 mm long, free: upper petals 7–8 × 4–5 mm, broadly oblong, apex truncate to slightly emarginate, base cuneate, pink; lower petals 10–11 × 4–5 mm, free, elliptic to obovate, apex truncate to slightly bilobed, pink, each with a yellow dot and dark pink dot at base. Stamens 5: filaments ca. 2.5 mm long, pale pink; anthers pale pink. Ovary ca. 2 mm long, ca. 1 mm in diam., 5–carpellate, green, pilose. Fruits 15–20 mm long, 4–5 mm in diam., short fusiform, 5–lobed, green, pilose. Seeds 6–7, ca. 3 mm long, ovoid, brown.

Phenology:— Flowering from September to October; fruiting from September to October.

Distribution:— Endemic to northeastern Myanmar (Shan State), where it is known only from the type locality.

Ecology:— Growing in shady areas on a mountain summit in open fragmented evergreen forest, 1500–1600 m elevation.

Proposed IUCN conservation assessment:— Critically Endangered B1ab (i, ii, iii). This species is only known from a small population from a single locality. The extent of occurrence is estimated to be <5 km ( IUCN 2012).

Etymology:— The specific epithet is derived from its broadly oblong upper lateral petals.

Note:— This species usually has four lateral sepals, rarely two, in contrast to other similar species which have only two sepals, e.g., I. patula , I. violiflora Hook. f. ( Hooker 1875: 457), I. curvipes Hook. f. ( Hooker 1905: 25 & 32), and I. florulenta .

Phylogenetic analysis: —The results suggest that this species is part of Impatiens subgen. Impatiens sect. Uniflorae ( Yu et al. 2015) ( Fig. 7 ) and closely related to the Burmese species I. florulenta and I. decurva rather than to the species it resembles most closely in morphological characters, i.e., I. patula from Thailand.

Pollination ecology: —We did not observe any animals visiting the flowers of the species. However, based on the possession of a long, broad spur, we predict that this species is pollinated by both bees and butterflies (cf. Ruchisansakun et al. 2016).

Figures

FIGURE 6. Impatiens oblongata. A. Habit; B. Front view of flower; C. Lateral view of flower; D, E. Fruit; F. Pedicel and Stamens; G. Upper lateral sepals; H. Lower lateral sepals; I. Lower sepal; J. Dorsal petal; K. Lateral united petals. Drawn by Saroj Ruchisansakun.

FIGURE 7. Impatiens oblongata. A. Lateral view of flower; B. Front view of flower; C. Habit in situ. Photographs by Saroj Ruchisansakun.