Didymocarpus lobulatus is similar to D. heucherifolius Handel-Mazzetti and D. salviiflorus W.Y. Chun in having a similar zygomorphic corolla and pink to pinkish-purple funnel-shaped to tubular corolla tube, but can be distinguished from the former by its densely eglandular and glandular pubescent peduncle (vs. villous in D. heucherifolius), bracts subulate to subulate-triangular (vs. elliptic) and margin sparsely crenate from the middle (vs. entire), calyx shallowly 5-lobed to or lobed about two-thirds of the calyx length from the base (vs. 5-lobed to the base). From D. salviiflorus, it differs by having subulate to subulate-triangular bracts (vs. semi-orbicular in D. salviiflorus), calyx lobes triangular but non-overlapping (vs. depressed oblong, overlapping at margin) and in size in ca. 5 × 2.5 mm (vs. 2–2.2 × 4–4.5 mm). It is also similar to D. cortusifolius in the shape and size of the leaves, but can be easily distinguished by having bracts subulate to subulate-triangular (vs. ovate to elliptic in D. cortusifolius), bract margin sparsely crenate from the middle (vs. entire), larger calyx lobes ca. 5 × 2.5 mm (vs. 1–3 × ca. 2 mm) and lobes’ margin nearly entire to entire (vs. denticulate), corolla white (vs. corolla pink to dark pink), fertile stamens adnate to corolla ca. 5 mm from base (vs. adnate to corolla 10–14 mm from base), filaments sparsely brownish glandular-puberulous (vs. glabrous).

Figure 1. 

Didymocarpus lobulatus A Habit B Flower in top view C Opened corolla, showing stamens and staminodes D Fertile stamens and anthers E Pistil, disc and stigma.

CHINA. Zhejiang Province: Shengzhou city, Chongren Town, Liwang village, 29°39'N, 120°39'E, 223 m a.s.l., 23 May 2014, flowering, Wen-Yuan Xie & Jia-Jun Zhou 140523-01 (holotype: IBK; isotype: AHU).

Perennial acaulescent herb. Rhizome horizontal, 1–4 cm long, up to 1.5 cm in diameter, roots fibrous. Leaves 4–8 basal, clustered at the apex of the rhizome; petioles terete, 2–9 cm long, densely covered with spreading rust-brown villous and white puberulent indumentum; blades asymmetrically orbicular-ovate to orbicular triangular, 3–10 × 2.5–12.5 cm, apex rounded, base cordate, margin irregularly triangular denticulate, papery, upper surface densely covered with whitish short and long eglandular pubescent indumentum, green, lower surface sparsely covered with hairs as on upper surface confined to the veins, pale green, basic veins 3–6, obscure above, prominent beneath. Inflorescences axillary, cymes 1–2-branched, 3–8 (–12)-flowered; peduncle 3–16 cm long, densely covered with both eglandular and glandular pubescent hairs, pedicel 0.3–2 cm long, with indumentum as on the peduncle. Bracts 2, opposite, subulate to subulate-triangular, ca. 8 mm long, adaxially glabrous, abaxially puberulent, margin sparsely crenate from the middle; bracteoles 2, opposite, subulate, 3–3.5 mm long, indumentum same as bracts. Calyx actinomorphic, shallowly 5-lobed to about two-thirds of the calyx length from the base, symmetrical, 1.3–1.6 cm long, inside glabrous, outside densely puberulent, brownish-green; lobes equal, triangular, ca. 5 × 2.5 mm, apices obtuse, margin nearly entire to entire. Corolla zygomorphic, 2.5–3.2 cm long; outside sparsely puberulent to glabrescent, inside glabrous, pink to dark pink, becoming pinkish-white at the base, with brown lines inside. Tube funnel-shaped to tubular, 1.8–2.2 cm long, 0.8–1 cm in diameter at mouth; limb distinctly 2-lipped, adaxial lip 2-parted to near the middle, lobes ovate, ca. 6 × 5 mm, abaxial lip 3-lobed from the base, lobes oblong, ca. 8 × 4 mm, more or less equal. Fertile stamens 2, adnate to corolla ca. 0.5 cm from base; filaments slender, 6–10 mm long, geniculate near the base, sparsely brownish glandular-puberulous; anthers fused along their entire adaxial surfaces, reniform-oblong, 1.8–2.5 mm long, ca. 2 mm wide, pale yellow, bearded on the back; staminodes 3, reduced to capitate, 0.3–0.5 mm long, adnate to corolla 6-8 mm from base, brown. Disc cylindrical, ca. 2 mm long, margin irregular, glabrous. Pistils 2–3 cm long, densely puberulent with both glandular and eglandular hairs; ovary ca. 2.6 cm long, yellowish-green. Stigma 1, terminal, depressed-globose, undivided, translucent. Capsule 5.5–7 cm long, brownish, glabrous.

Figure 2. 

Didymocarpus lobulatus F. Wen, Xin Hong & W.Y. Xie. A Habitat B Vegetative part of plants C Habitat in flowering D Frontal view of corolla E Top view of cyme, showing actinomorphic calyx F Opened corolla for showing stamens, pistil and calyx lobes G Adaxial surface view of leaf blade H Abaxial surface view of leaf blade.

The specific epithet is derived from the shallowly 5-lobed calyx.

Didymocarpus lobulatus is locally abundant and endemic to a narrow area in eastern China, surrounding the type locality. This species grows on moist shady cliffs of sandy shale hills, at an elevation of 223 m a.s.l. in type locality. The average temperature is 16.4 °C, the average annual precipitation has been calculated as ca. 1,446.8 mm. The forest is a subtropical monsoon climate evergreen broad-leaved forest. Flowering in May. Another population growing in the Danxia landscape of Chuanyanshijiufeng, Xinchang County, Shaoxing city, not far away from the type locality, was discovered by the first author in 2016. The two places are about 40 kilometres apart.

Based on the present field investigations, Didymocarpus lobulatus is currently only known from two sites around the type locality. The two places are about 40 kilometres apart. The type population, which grew close to a country road, is potentially threatened by human activities. Although no such habitat destruction is currently occurring, this population is likely to be threatened in the foreseeable future under influences of man-made factors, for example, by road widening. Fortunately, the second population has been found in the well-protected core zone of the scenic spot, Chuanyanshijiufeng. Furthermore, this population is healthy and locally abundant with many young plants and seedlings growing in the area. Thus, it seems that this species is not at serious risk now and it is proposed as ‘Vulnerable’ (VU D2) according to the IUCN Red List Categories and Criteria (IUCN 2016).

The geographical distributions of Didymocarpus lobulatus and its congeners are identified in Map 1. There are altogether 7 species and one variety of sect. Heteroboea, three species are endemic to East China (Didymocarpus salviiflorus and D. cortusifolius in Zhejiang prov. and D. dissectus in Fujian prov.) and two species and one variety (D. yuenlingensis W.T. Wang, D. sinoprimulinus W.T. Wang and D. heucherifolius var. yinzhengii) endemic to Hunan prov. of South China. Only one species, Didymocarpus heucherifolius, is widespread, being distributed from northern Guangdong prov. of South China, to Jiangxi prov., Fujian prov., Anhui prov. and Zhejiang prov. of East China. As more and more field investigations are undertaken, the biodiversity of sect. Heteroboea in East and South China will be better understood by researchers. The discovery of two new taxa, Didymocarpus dissectus Fang Wen, Y.L. Qiu, Jie Huang & Y.G. Wei (2013) and D. lobulatus, serve as two good examples. Differences between the new species and its morphologically related species in sect. Heteroboea in Zhejiang prov. are shown in the following identification table (Table 1) and Figure 3.

Map 1. 

The distribution areas of Didymocarpus lobulatus and its congeners in Zhejiang prov.: ➀ D. lobulatus ➁ D. cortusifolius ➂ D. salviiflorus ➃ D. heucherifolius (in semi-elliptical region, the arrows point).

CHINA. Zhejiang Province: Shaoxing city, Xinchang County, Chuanyanshijiufeng, Danxia landscape, secondary forests, 29°23'N, 120°48'E, 248 m a.s.l., 11 November 2018, in fruit, WYG181111-01 (IBK!).

Figure 3. 

A Didymocarpus lobulatus B D. heucherifolius C D. cortusifolius D D. salviiflorus 1 Habitats 2 The frontal view of corolla and cyme 3 Cyme and bracts 4 calyx lobes.