China, Yunnan Province, Jinping County, Maandi, alt. 1650 m a.s.l., 22°46'19.97"N, 103°28'29.78"E, 10 September 2016, Lei Cai & Z.Y. Yu CL16050 (holotype:1498854, KUN!; isotypes:1498855, KUN!).

This species is similar to Impatiens parvisepala S.X. Yu & Y.T. Hou (2011: 57) (Hou et al. 2011) in its racemose inflorescences, its alternate and aggregated or subverticillate at stem apex arrangement leaf, and its yellow flowers, but it can be distinguished by its conspicuous 0.5–2.4 cm long petiole (vs. sub-sessile or sessile), its shorter 10–35 cm high plants (vs. 35–60 cm high), its 3.5–12 × 1.5–4 cm elliptic to lanceolate-oblong leaf blades with cuneate bases (vs. 12–20 × 3.5–6 cm obovate or obovate-lanceolate blade with attenuate bases), its slightly incurved or narrowing to incurved spur (vs. nearly straight spur), and its racemose inflorescences with up to 22 flowers (vs. 6–8 flowers per inflorescence).

Figure 1. 

Impatiens wutaishanensis R.L. Liao & Lei Cai A habit B whole plant C inflorescence D capsule E flower in front view F flower in lateral view G different parts of the flower.

Figure 2. 

Impatiens wutaishanensis R.L. Liao & Lei Cai (drawn by R.M. Zhang) A habit B root C inner lateral sepal D outer lateral sepal E dorsal petal F lateral united petals (F1: upper petal F2: lower petal) G lower sepal H ovary and stamens I flower in front view J flower in lateral view K partial view of leaf margin.

Perennial herb, 10–35 cm tall, glabrous. Root-system shallow, with runners and adventitious roots. Stem fleshy, erect, simple, lower nodes swollen. Leaves simple, alternate, aggregated or subverticillate at stem apex; petiole 0.5–2.4 cm long, leaf blade 3.5–12 × 1.5–4 cm, elliptic, lanceolate, or lanceolate-oblong, base cuneate, margin roughly crenate, mucronulate, apex acuminate, adaxial surface dark green, abaxial surface pale green, lateral veins 4–8 pairs. Racemes in the upper leaf axils, 1–4, 4.2–28 cm long, erect, each with up to 22 flowers. Pedicels 0.6–2.5 cm long, bracteate at base. Bracts ca. 8 mm long, lanceolate to subulate, apex acute, base obtuse, margin entire. Flowers yellow. Lateral sepals 4, light green, the outer pair ca. 5–8 × 3–4 mm, ovate or obovate; the inner pair ca. 8–13 × 1–3 mm, sickle-shaped, obliquely lanceolate, apex acuminate or caudate. Lower sepal 1.5–2.2 × 1.2–2 cm excluding the spur, yellow to yellowish green with reddish patches, obliquely infundibuliform, base gradually constricted into a spur, spur 1.2–3 cm long, slightly incurved or narrowing to incurved, apex rostellate. Dorsal petal 1.3–2.3 × 0.7–1.6 cm, yellow with nearly transparent base, obovate to ovate, apex acuminate, with an inconspicuous dorsal crest, base truncate or cuneate. Lateral united petals ca. 1.6–3 cm long, yellow with nearly transparent base and reddish patches; the upper petals ca. 1.5–2.3 × 0.7–1 cm, oblong; the lower petal ca.1.2–1.8 × 0.6–0.8 cm, reniform. Stamens 5, filaments linear, ca. 3 mm long, anthers obtuse. Ovary fusiform, slightly curved. Placentation axile with four locules. Capsule (immature) clavate, 2–2.5 cm long.

Pollen grains triangular-round with three equal sides in polar view, and the equatorial view is elliptic, long-elliptic, P×E=16.56±1.78 (14.51–21.73)× 30.00±0.98 (28.35–32.11) μm. 3-colpate, linear, the entire surface is covered with reticulate ornamentation, granules in lumina (Fig. 3).

Figure 3. 

Micromorphology of Impatiens wutaishanensis R.L. Liao & Lei Cai under cryo-SEM A–D pollen A polar view B equatorial view C partial view D total view E–F leaf surface E adaxial epidermis F abaxial epidermis. Scale bar: 2 μm (A, B); 1 μm (C); 20 μm (D–F).

The anticlinal walls of the epidermal cells on the adaxial surfaces are straight, while those of the abaxial surface are sinuate. The stomata only appeared on the abaxial surface of the leaf, the shape was anomocytic and the outline of the guard cells was suborbiculate (Fig. 3).

This new species was observed flowering from August to November, and fruiting from September to December.

This species is currently known from only two small subpopulations less than 10 km away (Shidong and Biaoshuiyan) in Jinping County of Southeast Yunnan, China (Fig. 4). The distribution area is very close to the border between China and Vietnam. We assume that this species should be distributed in Vietnam due to its similar habitat and proximity to the type locality, which will be verified by future investigation.

Figure 4. 

Distribution of Impatiens wutaishanensis R.L. Liao & Lei Cai and I. parvisepala S.X. Yu & Y.T. Hou.

This new species has a runner with adventitious root produced from the nodes and was collected growing in the understory of forest at an elevation of 1300–1650 m. In the subpopulation in Shidong, the plants found coexist with the cultivated Amomum tsaoko Crevost & Lemarie (Zingiberaceae). In the subpopulation in Biaoshuiyan, the plants were found beside the artificial trail in a scenic area. The main accompanying species were Begonia Linn. sp. (Begoniaceae), Didymocarpus purpureobracteatus W.W. Smith (Gesneriaceae), Epigeneium amplum (Lindl.) Summerh. (Orchidaceae), Hedychium villosum Wall. (Zingiberaceae), Polygala fallax Hemsl. (Polygalaceae) and Vaccinium Linn. sp. (Ericaceae).

This species is currently known only from Jinping County, Yunnan, China with one type locality and a subpopulation. The Extent of Occurrence (EOO) is less than 100 km² and the known Area of Occupancy (AOO) is less than 15 km². The conservation status can be evaluated as Vulnerable (VU) D2 based on IUCN Red List Categories and Criteria (IUCN 2019). About 350 and 200 individuals were known in the two subpopulations of Biaoshuiyan and Shidong, respectively, and both are exposed to human disturbance. Therefore, we assess this species as a Plant Species with Extremely Small Populations (PSESP) (Yang et al. 2020).

The specific epithet ‘wutaishanensis’ refers to the type locality where the new species was found, located in the Wutaishan area of Jinping Fenshuiling National Nature Reserve, Jinping County, Southeast Yunnan, China. The Chinese name is given as “五台山凤仙花”.

Paratypes. China. Yunnan Province: Jinping County, Maandi Town, Shidong. 22°46'19.97"N, 103°28'29.78"E, 1650 m a.s.l., 5 August 2015, Lei Cai et al., CL155 (KUN!); The same locality, 2 August 2020, R.L. Liao & X.Y. Li, LRL202008003 (KUN!); Yunnan Province: Jinping County, Maandi Town, Biaoshuiyan, 22°43'56.61"N, 103°30'36.58"E, 1311 m a.s.l., 2 August 2020, R.L. Liao & X.Y. Li, LRL202008001 (KUN!)

The new species is most similar to Impatiens parvisepala in its racemose inflorescence, its yellow flowers with four lateral sepals. However, I. wutaishanensis is usually a shorter plant and its petiolate leaf blades are smaller and elliptic, lanceolate, or lanceolate-oblong. Its nectar spur is slightly incurved or narrowing to an incurved spur, and each inflorescence may have up to 22 flowers (Figs 1, 2). In contrast, the plants of I. parvisepala are taller, the sessile or subsessile leaf blades are larger and obovate or obovate-lanceolate, the spur is nearly straight and the number of flowers per inflorescence is 6–8 (Hou et al. 2011; Son et al. 2015). The distribution of these two species is geographically isolated from each other: Impatiens wutaishanensis, is confined to Southeast Yunnan Province with two subpopulations, where the I. parvisepala is recorded in western Guangxi and northern Vietnam (Fig. 4).

In order to illustrate the morphological circumscription of the new species, we compare the new species with four species with similar morphological characters in Table 1: Impatiens apalophylla Hook. f. (1908:243), I. clavigera Hook. f. (1908:2863), I. parvisepala and I. tianlinensis S.X. Yu & L.J. Zhang (2015: 253) (Zeng et al. 2015).