Impatiens karenensis resembles I. micromeris, but differs in having lower petals with outer margins strongly undulate in the lower-half (vs. lower petals entire), apex of upper petals acute to obtuse (vs. rounded), short stout spur, ± as long as the depth of lower sepal, ca. 2.5 mm long (vs. long attenuate spur, twice as long as the depth of lower sepal, ca. 5 mm long).

Figure 1. 

Impatiens karenensis Chit Soe Paing & Ruchis A habit B flower, front view C flower, side view D inner lateral sepals E outer lateral sepals F–H lower sepal I–J dorsal petal K lateral united petals L ovary, pedicel and bract M fruit (from Chit Soe Paing 002). Drawn by S. Ruchisansakun.

Myanmar. Kayin State (Karen State), Hpa-an, Ta Yoke Hla (Kawt Kyaik), 16°50'31.4"N, 97°37'10.4"E, 100–150 m a.s.l., 16 Oct 2023, Chit Soe Paing 002 (holotype RAF!, isotype RAF, RANG).

Figure 2. 

Impatiens karenensis Chit Soe Paing & Ruchis. in vivo A flower, front view B flowers, side view C habit. Photographed by Chit Soe Paing.

Lithophytic annual herbs, 50–70 cm tall. Stems erect, laxly branched near the top, green to red to purple with red dots, glabrous; hypocotyl elongate, 1–2 cm in diam., epicotyl slightly zigzag in the upper parts. Leaves spirally arranged, congested on the top when young; petiole ca. 2 cm long, ca. 1.3 mm in diameter, green to reddish-green; lamina ovate, 4–5 × 2.3–2.5 cm, apex acute, base cuneate, green above, paler green below, glabrous, margin serrate with teeth, with a pair of linear glands at the margin near the base, lateral main veins 4–6 pairs. Inflorescence axillary, 2-flowered fascicle; bracts linear-lanceolate, ca. 2 mm long. Flowers white with yellow patch and two yellow streaks at the lip base, 19–19.5 × 6–7 mm, 7–8 mm deep; pedicel 1.6–1.7 cm long, green to reddish-green, glabrous. Lateral sepals 4; inner pair ovate, 0.6–0.7 × 0.5–0.6 mm, apex round, green, glabrous; outer pair free, ovate, ca. 3 × 2 mm, apex acute, green, glabrous. Lower sepal navicular, 7–9 × 5–5.5 mm, 2–3 mm deep, light green, apex acute and mucronate, abruptly constricted into a short strait green spur, ca. 2.5 mm long. Dorsal petal 5.4–5.6 × 6.5–7.5 mm, broadly ovate to broadly obovate to suborbicular, green at the margin and apex, apex emarginate-mucronate, mid-vein crested, ca. 0.5 mm high. Lateral united petals connate, white with yellow mark in the middle at ca. ¼ from the base, clawed to 2–3 mm long; upper petals, 3–3.5 × 1.5–2 mm, ovate to triangular, apex acute to obtuse; lower petals 1.4–1.52 × 0.34–0.35 cm, narrowly ovate in outline, apex obtuse-slightly bilobed, base with two small triangular projections, outer margins strongly undulate in the lower half. Stamens ca. 3 mm long. Ovary 4-loculate, ca. 3 mm long, green, glabrous. Fruits clavate, 4-lobed, ca. 9 mm long, green, glabrous with green to red pedicel. Seeds unknown.

Grows in open areas on small limestone mountains, 100–400 m a.s.l. Flowering. August–October, fruiting October–November.

Endemic to Myanmar. This species is only known from the two localities, around 2 km apart (Fig. 3).

Figure 3. 

The distribution of Impatiens karenensis Chit Soe Paing & Ruchis. (SimpleMappr, Shorthouse 2010).

The specific epithet is derived from the former name of the state of its type locality “Karen”.

Impatiens karenensis is currently found at two locations outside of the protected area. This species has a limited extent of occurrence (EOO) and area of occupancy (AOO), spanning less than 10 km² (GeoCAT, Bachman et al. (2011)). The population of mature individuals is known to fluctuate. Moreover, the habitat quality is consistently declining because of warmer and drier conditions, particularly by El Niño, coupled with invasive species encroachment. Based on these significant threats, we strongly recommend designating Impatiens karenensis as Critically Endangered (CR; B1+B2ac(iv)) according to the IUCN Categories and Criteria (IUCN Standards and Petitions Committee 2024).

Impatiens karenensis shares similarities with I. micromeris and other small Semeiocardium species. It also bears resemblance to I. suksathanii, but differs in having undulate margin lower petals (vs. entire margin lower sepals), white flower (vs. pink or yellow flower), ovate leaves (vs. linear to narrowly elliptic leaves) (Suksathan and Ruchisansakun 2022).