Primulina serrulata mainly differs from its congener, P. fimbrisepala, by its purplish-blue flowers which lack the dark purple spots inside the corolla (vs. purple to purplish-pink, with bright dark purple spots inside the corolla), cuneate leaf blade base (vs. obliquely cuneate, broadly cuneate or cordate), anthers glabrescent (vs. sparsely bearded) and smaller stigma ca. 1 mm long (vs. 2–3 mm long).

CHINA. Guizhou Province, Rongjiang County, Langdong town, growing on moist limestone rocks surfaces near waterfall, alt. 780 m, 26°07'N, 108°42'E, 17 April 2018 (flowering), Ren-Bo Zhang et al., ZRB1478 (holotype: ZY!; isotype: IBK!).

Figure 2. 

Primulina serrulata. A habit B adaxial leaf blade C cyme, bracts, flower in frontal view and flower in lateral view D opened corolla for showing stamens and staminodes E adaxial calyx lobes F pistil G cross section of ovary. Drawn by Tan Deng.

Rhizomatous stem subterete, ca. 6 cm long, ca. 1.5 cm in diameter. Leaves 4–6, all basal, opposite decussate. Petioles flatted, fragile and easy to be broken, 2–7 cm long, 4–5 mm wide, densely erect white multicellular hispid, hairs ca. 7 mm long. Leaf blade slightly fleshy and fragile when fresh, chartaceous when dried, obliquely ovate, oval to nearly rounded, 5–13 × 3–10 cm, densely erect white multicellular hispid and short hispid on both surfaces, base obliquely broadly cuneate, cordate to nearly rounded, margin conspicuously big and irregular serrate and biserrate; lateral veins 3–5 on each side, adaxially inconspicuously sunk but clearly slivery, occasionally green, abaxially conspicuously raised. Cymes 1–6, axillary, 1–2 branched, 2–5(8)-flowered; peduncles 11–16 cm long, ca. 2 mm in diameter, densely erect white multicellular hispid and short hispid; bracts 2, green, opposite, narrowly rhombic, 5–12 × 2–5 mm, margin inconspicuously serrate, apex acute, outside densely pubescent, inside pubescent; sometimes with bracteoles, opposite, 2, narrowly triangle, ca. 5 × 1 mm. Pedicel 2.5–5.5 cm long, ca. 1 mm in diameter, densely pubescent. Calyx 5-parted to near base, lobes oblong to lanceolate, green, 8–15 × 3–5 mm, outside densely pubescent, inside glabrous, apex subacute, margin entire about 2/3 of calyx lobe from the base but denticulate 3–4(5) about 1/3 of calyx lobe from the apex. Corolla pale purple to purple, the color of the throat same as corolla with two longitudinal yellow stripes along corolla tube but without dark purple spots, 4.5–6.0 cm long, outside glandular-pubescent and puberulent from the base to middle of corolla tube, inside glabrous; tube infundibuliform-tubular, 3.0–3.5 cm long, 1.0–1.5 cm in diameter at mouth, ca. 4 mm in diameter at base; limb distinctly 2-lipped, adaxial lip 2-parted, the upper part of the interior of two adaxial lip lobes with two lines of glandular hairs on the brown patch, lobes broadly ovate, 8–12 × 5–9 mm, apex rounded, abaxial lip 3-lobed, lobes oblong, 2.0–2.8 × 1.0–1.4 cm, apex rounded. Stamens 2, adnate to 10–13 mm above the corolla tube base; filaments linear, ca. 15 mm long, white, geniculate near the base, sparely puberulent from the middle to the top, the rest glabrous; anthers fused by the entire adaxial surfaces, ca. 4 mm long, glabrous. Staminodes 3, lateral ones 6–7 mm long, adnate to 12–15 mm above the corolla tube base, middle one ca. 1.5 mm long, adnate to 8–10 mm above the corolla tube base. Disc annular, the higher side ca. 1.5 mm in height but the lower side ca.0.8 mm in height. Pistil 3.5–4.5 cm long; ovary cylindrical, 2.5–3.2 cm long, densely glandular pubescent and puberulent; style 1–1.3 cm long, densely glandular-pubescent and puberulent; stigma obtrapezoid, apex 2-lobed, ca. 1 mm long, ca. 0.8 mm wide. Capsule linear, ca. 6 cm long, sparsely pubescent.

Figure 3. 

Primulina serrulata. A, C different shapes of adaxial leaf blades B, D different shapes of abaxial leaf blades E cyme, bracts, flower in top view F bracts and bracteoles G corolla in frontal view H corolla in lateral view I adaxial calyx lobes J abaxial calyx lobes K opened corolla L pistil. Charted by Wen-Hua Xu.

At this time, Primulina serrulata is only known from the type locality in Langdong village, Langdong town, Rongjiang County, Guizhou Province, based on our field investigations. It grows on moist, shady, limestone rocks near a waterfall, at ca. 780 m altitude, with no more than 150 mature individuals. The population is close to a road, which makes it vulnerable and subject to destruction from human activities.

This new species was observed flowering in April and fruiting from May to June.

The specific epithet is derived from its particular leaf blade margin, having obvious serrations and bi-serrations.

Because of Primulina serrulata’s beautiful leaves and flowers, it is being over-harvested by local people for sale. This unpublished species is therefore on the brink of extinction as a result. Before more surveys are completed to clarify its conservation status, the provisional conservation status is Critically Endangered CR B2ab (iii, v) according to the IUCN red list criteria (IUCN 2012).

Primulina serrulata is related to its congener, P. fimbrisepala, by some characteristics, for example, the similar calyx lobes and infundibuliform corolla tube, but they can easily be distinguished from each other by the characters summarized in the description below. Numerous dark purple spots were covered at the throat of the corolla, and this is one stably distinctive feature of P. fimbrisepala. It is noticeable in different populations of P. fimbrisepala from South China when they are flowering (Figure 4). Table 1 below has more detailed information on how to distinguish the two species. They also grow in different substrates. P. serrulata only grows in limestone areas, while P. fimbrisepala commonly appears in weakly acidic mediums and soils of sandstone or granite mountainous regions. The different growing habitats of the two congeners indicate that geographical isolation should be one of the reliable drivers pushing this genus, Primulina, to generate diversification and speciation (Gao et al. 2015, Kong et al. 2017, Wang et al. 2017, Yang et al. 2019).

Figure 4. 

The corolla throat character of Primulina serrulata’s congener, P. fimbrisepala. A from Wenzhou city, Zhejiang B from Ziyuan County, Guangxi C from Jinxiu County, Guangxi D from Ruyuan County, Guangdong. Photoed by Fang Wen, Charted by Wen-Hua Xu.