The new species resembles Stauranthera grandifolia in leaf blade shape and corolla, but can be easily distinguished from the latter in the flower number of cymes 2–4 bushes (vs. cymes 1–2 bushes), calyx colour white to slightly purple (vs. green), and bract 1, bracteole 1 auriculate connate (vs. bracts 2, linear opposite) and ovary 1–loculed (vs. 2–loculed) (Table 1).

China. Yunnan Province: Jinping Miao, Yao and Dai Autonomous County, Jinshuihe Town, Nawo, Rubber Forest, 22°37′42.30″N, 103°07′08.89″E, 316 m alt., 1 June 2023, Fan Su 2023061 (Holotype: IBK! IBK00451428; Isotypes: NPH! NPH 001940, NPH 001941, NPH 001942).

Perennial Herbs, terrestrial, not rhizomatous, up to 35 cm high. Stem 6–28 cm tall, 5–12 mm in diam., puce, pulverulent. Leaves opposite, usually three pairs, occasionally five pairs, with a normal leaf and a degenerated leaf at the internode, leaf blade strongly oblique, oblong to elliptic obovate, 14–28 cm long, 6–15 cm wide at the middle, apex acuminate, base cuneate on narrow side, broadly cuneate to rounded on wider side, margin nearly entire, adaxially glabrous, abaxially including leaf veins papillose-puberulent, lateral veins 10–13 on the narrow side; 13–20 on the wider side; petiole 4–6 cm long, ca. 4 mm in diam., puberulous; degenerated leaves, sessile, adaxially green, abaxially greenish, pubescent, cordate to auricular-cordate to auricular-renifor, 2–4 mm long, 8–12 mm wide, margin entire, apex retuse or emarginate, leaf vein 3 pairs. Inflorescence dichotomous cyme, emerging from the axils of the large leaves, 3–9 cymes per plant, dense flowers, 10–20, rare 5 flowers per cyme, peduncles, pedicels, bracts, calyx densely white pubescent, sticky, peduncle up to 18 cm high; pedicels 1.5–2 cm long; bract 1, bracteole 1, green, auriculate connated; calyx broadly campanulate, ca. 2 cm in diam., white to slightly purple, 5-lobed, lobes deltoid, margin entire, longitudinally wrinkled between lobes. Corolla slightly obliquely campanulate, purple or bluish-purple, throat yellowish; corolla tube ca. 5 mm long, orifice ca. 4 mm in diam., upper lip ca. 8 mm long, 2-lobed, lobes suborbicular, ca. 4 mm in diam., lower lip slightly smaller than the upper lip. Stamens 4, adnate to ca. 5 mm above the corolla base, glabrous, filaments linear, lilac, smooth, inside two ca. 5 mm long, ca. 0.5 mm in diam., outside two ca. 4 mm long, ca. 0.3 mm in diam.; anthers triangular to cordate, ca. 1.2 mm long, sides connected to each other, dorsal septum slightly raised. Pistil ca. 9 mm; Ovary yellowish, subuliform, ca. 5 mm long, ca. 4 mm in diam., 1-located glandular puberulent about the position from the top to 1/3 of the ovary, the rest of ovary glabrous; Style ca. 3 mm long, linear, sparsely glandular-puberulent from the bottom to 2/3 of the style, the rest of style glabrous; stigma 1, covered densely brownish puberulent hairs. Capsule globose to oblatoid, glabrous, brownish-purple when young, brownish-black when mature.

Figure 1. 

Stauranthera floribunda F.Su, C.Y.Hao & K.Tan, sp. nov. A habit B cymes C, D adaxial and abaxial views of the whole plant E degenerated leaves F front view of flower G back view of flower H detail of abaxial leaf blade I detail of stamens J detail of pistil K ovary and its cross-section view. Photographs by Fan Su.

Flowering in May and fruiting from June to July.

The specific epithet floribunda, which means “many-flowered”, refers the large numbers of the flowers per cyme and the whole plant of the new species. It is noticeably different from the flower numbers of all other known Stauranthera species.

Figure 2. 

Line drawing of Stauranthera floribunda F.Su, C.Y.Hao & K.Tan A adaxial view of the whole plant B front view of flower C back view of flower D detail of degenerated leaves E pistil F hair of abaxial leaf blade G frontal view of stamens H dorsal side of stamen. Drawn by Di Hu.

Chinese: 多花十字苣苔 (duō huā shí zì jù taí). The name ‘duó huá’ means it has more flowers than other species in this genus and ‘shí zì jù taí’ is the Chinese name of Stauranthera.

Up to date, Stauranthera floribunda is only known in Nawo of Jinshuihe Town, Jinping County, at an elevation ca. 316 m, near Vietnam, south of Yunnan Province, China. The main companion species were Alocasia odora (G.Lodd.) Spach, Pellionia radicans (Siebold & Zucc.) Wedd., Thunbergia grandiflora (Roxb. ex Rottler) Roxb. and Oplismenus compositus (L.) P.Beauv.

Since the only known population of Stauranthera floribunda is in the Rubber Forest of Jinshuihe Town, Jinping County, south Yunnan Province, we have not discovered the wild population expected from the above-mentioned location and information known about the population status and natural distribution range of the new species is very limited. Currently, less than 150 individuals have been found in the Rubber Forest. The new species of population, which grows close to a country road, is potentially threatened by human activities. Although no such habitat destruction is currently occurring, this population will likely be threatened in the foreseeable future under the influences of artificial factors, such as rubber cutting. Considering the known population is surrounded by rubber forests, it might survive under strong man-made intervention. Therefore, we suggest that the new species S. floribunda should be considered ‘Critically Endangered’ [CR, B2a,b (iii,iv,v)], facing a relatively high risk of extinction in the wild) according to current IUCN Red List Categories and Criteria (IUCN 2022).