Impatiens jenjittikuliae is most similar to I. lacei Hook.f. It differs from I. lacei by its densely pilose lateral sepal (versus glabrous) and by having no long hairs along its lamina margin (versus distinct long hairs especially along the lower-half of leaf margin).

THAILAND. Tak Province, Thasongyang District [17°30'1"N, 98°3'60"E], limestone area near waterfall in mixed deciduous forest at 540 m alt., 20 October 2018, S. Ruchisansakun 900 (holotype: QBG; isotypes: BK, BKF, Mahidol University Herbarium)

Lithophytic, annual herb, up to 6–30 cm tall. Stem erect, up to 1.2 cm in diam., cylindrical, branched, green, densely pilose with short white hairs. Leaves spirally arranged. Petiole 3–7.5 cm long, ca. 2.5 mm in diam., pale green to green to pink, pilose; with 5–7 pairs of long hairs on petiole, up to 2 mm long, green, sometime with red tips. Lamina 9–20 × 3–7 cm, ovate to elliptic, apex acute, base cuneate, margin shallowly serrate, adaxial green, abaxial pale green, pilose on both sides; lateral veins 10–12 pairs. Inflorescence raceme, axillary, 8–12 florets; peduncle 7–10 mm long, 1.5–2 mm in diam., pale green, densely pilose; rachis 8–20 mm long, ca. 1.5 mm in diam., pale green, densely pilose, hairs shorter than those on peduncle. Flowers ca. 20 × ca. 15 mm, ca 3 mm deep, pinkish white with reddish purple lip. Bracts ca. 1 × 0.5 mm, linear to narrowly lanceolate, apex acute, base cuneate, green, caducous, abaxial densely pilose with white hairs. Pedicel 12–15 mm long, less than 1 mm in diam., pink, densely pilose with white hairs. Lateral sepals 2, 5–6 × 6–7 mm, free, broadly ovate, the apex mucronate, the base truncate, pale pink, abaxially densely pilose with white hairs. Lower sepal 11–13 × 8–10 mm, ca. 14–17 mm deep, broadly navicular to subsaccate, apex acuminate and mucronate, white with green tip, densely pilose to strigose outside with long white hairs, distal part gradually constricted into a curved spur, 14–15 mm long, white to pale pink. Dorsal petal 11–12 × 14–15 mm, broadly ovate to obcordate, cucullate, apex emarginate and mucronate, base cordate, white to pale pink, densely pilose with white hairs, abaxial midvein with a white crescent-shaped crest, 1–1.5 mm high. Lateral united petals 20–24 mm long, free: the upper petals 9–10 × 10–11 mm, broadly oblong, apex truncate, base cuneate, upper outer part white to pale pink, lower inner part dark purple; the lower petals 17–19 × 8–10 mm, oblong, apex truncate, pink to reddish-purple; with a pink auricle at the base, ca 1 mm high. Stamens 5; filaments 4–5 mm long, white; anthers white. Ovary ca 4 mm long, 1.5–2 mm in diam., short fusiform, 5-carpellate, green, glabrous. Fruits, short fusiform capsule, 11–12 mm long, 6–8 mm in diam., subglobose, 5–lobed, green, glabrous. Seeds ca. 20 per fruit, ca. 1.34 mm long, ovoid, brown.

Pollen morphology : Pollen grains 4-colpate (Fig. 3A). Equatorial view oblong, ca 35 × 18–19 μm (length/width = 1.89); Polar view nearly elliptic, ca. 17 μm thick, colpi four, linear, ca 9–10 μm (Fig. 3A); surface entirely covered with numerous irregular lumens, 1.2–2 μm diam, lumens deep, sparsely granulate (Fig. 3B); muri slightly straight, joint of muri slightly corniculate (Fig. 3C).

Seed morphology : Brown ovoid, ca 1.34 × 0.93 mm, ca 0.51 μm thick (length/width = 1.44) (Fig. 4). Seed coat a composite of two types, thick finger-like cells, and inflated cells with granulate walls (Figs 4C, D).

Stem anatomy : Stem herbaceous, without lignification (Figs 5A–C). Only angular collenchyma for stem-strengthen were found (Fig. 5D).

Flowering from Oct. to Nov.; fruiting Oct. from Nov.

The new species is only known from the type locality in Tak Province, Thailand.

Impatiens jenjittikuliae grows on limestone close to waterfall in a mixed deciduous forest, 520–600 m elevation (pers. obs.).

Critically Endangered B1ab (i, ii, iii) + 2ab (i, ii, iii). This species is only known from the type locality; the extent of occurrence is estimated to be less than 5 km, where it occurs as a small population (IUCN 2012).

The new species is named in honor of Dr. Thaya Jenjittikul who encouraged the first author to step in and study this lovely plant family.

The author observed five visitations by bees from the family Apidae (identified by an entomologist, Pornpimon Tangtorwongsakul) during the expeditions. The size of bee body fit well with the floral entrance (Fig. 6). Moreover, the floral structure of this new species is similar to other bee-pollinated species, e.g. I. psittacina (Ruchisansakun et al. 2016). Hence, we concluded that it is a bee-pollinated species.

Figure 1. 

Impatiens jenjittikuliae. A Habit B Flower, front view C Inflorescence with flower in lateral view D Lateral sepals E Lower sepal F Dorsal petal G Lateral united petals. Drawn by Saroj Ruchisansakun.

Figure 2. 

Impatiens jenjittikuliae A flower, front view B flower, lateral view C habit in situ. Photographs by Saroj Ruchisansakun.

Figure 3. 

Pollen of Impatiens jenjittikuliae (FE SEM) A entire pollens B, C sexine ornamentation.

Figure 4. 

Seed of Impatiens jenjittikuliae (FE SEM). A, B Entire seeds C Inflated cells with granulate walls D Thick finger-like cells.

Figure 5. 

Stem of Impatiens jenjittikuliae, transverse sections.

Figure 6. 

Floral visitation by bee in the locality of Impatiens jenjittikuliae.