China; center of Guizhou Province, Zijiang gorge, Kaiyang County, grows on cliffs under forests along the road; alt. 1000–1020 m. 2009-08-18, Shun-Zhi He 90819 (Holotype: HGCM!, isotype: GNUB!, IBK!) (Figs 1, 2).

Figure 1. 

Hemiboea kaiyangensis T.Peng & S.Z.He A habit, showing flowering branch B opened corolla, showing stamens, staminodes and ring of hairs at base of tube C calyx, pistil and disc D stigma E stamens F infructescence G cross section of ovary, showing parietal placentation. Drawing by S.Q.He and Y.X.Zhu.

Hemiboea kaiyangensis is most similar to H. longisepala Z.Y.Li, H. flaccida Chun ex Z.Y.Li and H. ovalifolia (W.T.Wang) A.Weber & Mich.Möller in the glabrous pistil, but it differs in the cordate involucre bracts that are early deciduous, the corolla densely glandular puberulent outside and glabrous inside, and pale yellowish-green to pale yellowish-white outside.

Figure 2. 

Hemiboea kaiyangensis T.Peng & S.Z.He A habitat B plant with flowering branches C involucrum, early deciduous, before flower opening D pair-flowered cymes E calyx, disc and pistil F opened corolla, showing stamens, staminodes and ring of hairs at base of tube G cross section of capsule, showing two parietal placentation H seeds. Scale bar: 0.5 mm (Based on the holotype Shun-Zhi He 90819).

Perennial herb. Rhizomatous. Stems 25–60 cm long, 5–7 mm in diam., densely pubescent. Petiole 0.5–4.5 cm long, densely pubescent. Leaf blade herbaceous, oblique, iso- to distinctly anisophyllous, ovate or ovate-oblong, 13–26 × 5–8 cm, apex acute, base oblique cuneate, margin nearly entire or unapparent sinuous dentate, appressed pubescent on both sides, lateral veins 7–10 on each side. Cymes 2–3, terminal or subterminal, 6–12 flowers per cyme; peduncle 10–18 cm long, densely pubescent with white long glandular hairs; involucre cordate, apex cuspidate, early deciduous; pedicel 0.7–1.5 cm long, pubescent with white long glandular hairs. Calyx lobes 5; lobes oblong-lanceolate, apex obtuse or slightly obtuse, 12–13 × 2.5–3 mm, outside densely pubescent with glandular hairs of 3–4 mm long, inside glabrous, 3 veins per lobe. Corolla pale yellowish-green to pale yellowish-white outside, small purplish-brown spotted inside, 4.5–5 cm long, densely glandular-puberulent outside, glabrous with a ring of white hairs ca. 4 mm above the corolla base inside; tube 3.5–4 cm long, mouth 1–1.3 cm in diam.; limb distinctly 2-lipped, adaxial lip 2-lobed, lobes obliquely semicircular, apex obtuse to rounded, 6–7 mm long, 8–9 mm in diam. at the base of lobes; abaxial lip tripartite, lobes margin ciliolate, the central broadly ovate to ovate-elliptic, 6–7 mm long, two lateral oblique triangle, 7–8 cm long. Stamens 2, glabrous, adnate to 1.8 cm above the corolla base, filament ca. 1.3 cm long, geniculate at the middle; anthers slightly oblong, dark purple, apex coherent. Staminodes 2, glabrous, adnate to 1.7 cm above the corolla base, ca. 7 mm long. Nectary disc ring-like, 1.1–1.2 mm high, atop with ca. 6 obviously erose crena. Pistil 2–2.8 cm long, ovary 7–9 mm long, glabrous, style 1.4–2 cm long, glabrous, stigma 1, terminal truncate, sightly 2-lobed. Capsule obliquely linear-lanceolate, 2–2.4 cm long, 3–3.3 mm in diam., glabrous, slightly curved.

Figure 3. 

Strict consensus tree of three parsimony trees based on combined ITS and trnL-F data. Numbers above branches are bootstrap values. Underline indicates the new species.

Pollen grains of Hemiboea kaiyangensis are prolate-spheroidal, long or oblate, 3-colporoidate grains. In polar view, the outline is close to triangular-circular. The ectocolpi measures 33.05–33.57 × 12.15–14.23 μm and the endoapertures are laterally fused to form an endocingulum. Exine reticulate, muri smooth. The width of muri is unequal in size. The sizes and shapes of perforations are irregular, and vary in size from 0.14–0.67 × 0.11–0.61 μm.

Known only from a single limestone gorge in Kaiyang county, Guizhou Province, China. Only five populations were found, growing on the mouth of caves in shady and damp forests, close to a road, between 900 and 930 m in elevation.

The name of the new species, kaiyangensis, refers to the type locality, Kaiyang County, Guiyang, Guizhou Province, China.

The populations of Hemiboea kaiyangensis are endemic to Kaiyang county, center of Guizhou Province, China, and the species only known from the type locality at present. The five detected populations grow dispersed in a limestone gorge, and cover only an area of about 1.25 km² and include a total of 75–120 individuals. However, until further investigation, the species should be designated as “Data Deficient” (DD) according to the IUCN standards (IUCN 2019).

As previously mentioned, Hemiboea kaiyangensis is most morphologically similar to H. longisepala, H. flaccida and H. ovalifolia in their glabrous pistil, but some characters, such as the early deciduous and cordate involucre bracts, the corolla indumentum (outside densely glandular puberulent and inside glabrous), and the corolla color (outside pale yellowish-green to pale yellowish-white), help us to easily distinguish them. Specifically, H. kaiyangensis is similar to H. flaccida in having two staminodes, but it differs in the longer peduncle (10–18 cm), the involucre cordate but early deciduous, the bigger calyx lobes, oblong-lanceolate (12–13 × 2.5–3 mm), and the glabrous pistil. This new species is also similar to H. ovalifolia in the texture and shape of leaf blade, but it can be distinguished in the peduncle indument, with dense white long glandular hairs, the involucre cordate, the calyx lobes outside densely glandular pubescent, the corolla outside densely glandular puberulent, 2 staminodes, and the pistil glabrous. Lastly, H. kaiyangensis is similar to H. longisepala, but it differ from the latter in the stem densely pubescent, the longer peduncle (10–18 cm), the peduncle with dense white long glandular hairs, the corolla outside densely glandular puberulent and 2 staminodes. All compared details of four congeners were listed in Table 2.