China. Guangdong: Shaoguan City, Renhua County, Mount Danxia, 24°56'29.73"N, 113°45'21.96"E, dry mountaintop, ca. 350 m elev., 23 May 2020, Q. Fan 17910 (holotype: SYS!; isotypes: SYS!, IBSC!).

Figure 3. 

Commelina danxiaensis sp. nov. A habitat B involucral bract C inflorescence D flower E fertile, sterile stamens and pistil F fruit in transverse section G seed.

Commelina danxiaensis is morphologically similar to C. communis due to their diffuse stems, lanceolate leaf-blades and approximate floral forms. However, it differs in its ascending stems (Fig. 4B), tomentose leaf-blades and sheaths (Fig. 4C–F), and sky-blue lateral petals with a white basal third (Fig. 4G).

Figure 4. 

Commelina danxiaensis sp. nov. A habitat, growing on top of the Danxia landform B habit, plants ascending C–E leaf-blade, lanceolate to ovate-lanceolate F leaf-sheaths, with pubescence G–H flower I inflorescence J spathe K fruit in transverse section, 2 seeds per valve L seed. Scale bars: 1 cm (D, E, G, I, J); 3 mm (K, L).

Herbs over 30 cm tall, annual. Roots thin, fibrous. Stems ascending, many-branched; young shoots tomentose, becoming glabrous when old, hairs hyaline. Leaves spirally-alternate, evenly distributed along the stems; sheaths tomentose, hairs hyaline, margin ciliate, hairs setose, white; blades 3–9 × 1.5–2.0 cm, lanceolate to ovate-lanceolate, tomentose on both sides, evently, hairs hyaline, base obtuse, margin glabrous, green to light-purple,, apex lanceolate. Inflorescences leaf-opposite, restricted to the apex of the stems; peduncle 1.5–4.0 cm long, tomentose, hairs hyaline; spathe 1.2–2.5 × 1.0–2.2 cm, cordate, 6–8 veined, adaxially tomentose, long pilose hairs sometimes along the veins, hairs hyaline, abaxially glabrous, base cordate, free, margin green, apex acute; upper cincinnus developed, 1-flowered, flower staminate, peduncle ca. 8 mm long, exerted, sparsely tomentose to nearly glabrous, hairs hyaline; lateral cincinnus 2–3-flowered, flowers bisexual, peduncle 5–8 mm long, nearly included, tomentose to nearly glabrous, hairs hyaline. Flowers chasmogamous, bisexual or staminate, strongly zygomorphic; pedicels c. 3 mm long at anthesis, less than 6 mm long in fruit, reflected, nearly glabrous, hairs hyaline; sepals green, membranous, glabrous, dorsal sepal c. 5 × 2 mm, triangular-lanceolate, apex lanceolate, lateral sepals c. 5 mm × 3 mm, widely oblique-elliptic, connate for 3.6–4.2 mm, apex obtuse to round; paired petals short-clawed, claw c. 2–3 mm long, limb c. 1 cm × 1 cm, orbicular to sub-orbicular, sky-blue with a white basal third, medial petal c. 5 × 2 mm, narrowly rhombic, white, nearlly hyaline; staminodes 3, subequal, the medial slightly shorter, filaments c. 3 mm long, antherodes X-shaped, distinctly four-lobed, upper lobes c. 1/2 to the lower ones, yellow, with a dark maroon at centre; lateral stamen filaments ca. 1 cm long, curved, anthers 1.8–2.2 × 1.2–1.4 mm, elliptic; medial stamen filament ca. 5 mm long, anther 2.2–2.4 × 1.8–2.2 mm, saddle-shaped; ovary c. 1 × 1 mm, ovoid, glabrous, 2-locular, ovules 2 per locule, style c. 1.2 cm long, strongly curved at apex, stigma trilobate, white. Capsule c. 5 × 3 mm, ellipsoid, glabrous, equally 2-valved. Seeds 2 per valve, 3–4 × 2–2.5 mm, elliptic, ventrally flattened, testa brown, irregularly pitted.

Commelina danxiaensis flowers from April to July and fruits from June to September.

Commelina danxiaensis is only known from the type locality, Mount Danxia, Renhua County, Guangdong Province, China. Only two populations have been found, with several hundred individuals. It grows on dry mountaintops of the Danxia formation at elevations of 100–350 m.

Commelina danxiaensis has only been found in Mount Danxia within an area of less than 20 km², making it putatively ‘Vulnerable’ (VU D2) according to the guidelines of the IUCN Red List Categories and Criteria (IUCN 2022). However, the threat risk seems low because it is not economically valuable, and the area’s conservation is good.

(paratypes). China. Guangdong: Shaoguan City, Renhua County, Mount Danxia, fl., 3 July 2020, Q. Fan 18026 (SYS); loc. cit., fr., 29 August 2020, Q. Fan 18231 (SYS); loc. cit., fr., 29 August 2020, Q. Fan 18232 (SYS).

The new species Commelina danxiaensis is similar to C. communis and C. diffusa in some of its morphological characters, such as lanceolate leaf-blades, cordate spathes free at base, and blue paired petals. Morphological comparisons among them have been listed in Table 1.

Additionally, we found the name Commelina bicolor D.Q.Wang & M.E.Cheng described by Wang et al. (2019), which is a later homonym of C. bicolor Poepp. ex Kunth (1843). Therefore, it is illegitimate under Art. 53.1 of ICN (Turland et al. 2018). This species is documented in Anhui and Hubei Provinces, and the type specimen (D.Q. Wang, Y.Y. Lu & L. Zhang W1406291, PE) was collected at Daqian Shan of Feixi County in Anhui Province (Wang et al. 2019). We previously believed the unknown species of Commelina in Mount Danxia to be conspecific with C. bicolor due to its similar morphological and ecological characteristics and treated it as a new distribution record for the Guangdong flora (Dai et al. 2021). However, we have been unable to check the type material at PE, where the authors stated the holotype specimen was deposited, to confirm the plant’s identity and the name’s application. We carried out fieldwork at Daqian Shan but were unable to find any individuals of this species. Hence, treatment has not been made for this species at the moment. It is planned that a further study will be carried out in the future.

Up to the present time, four species of Commelina have been documented in Danxiashan National Nature Reserve, including the new species Commelina danxiaensis. In order to facilitate identification, we here provide a key and checklist for the Commelina species in Mount Danxia.