The new taxon has a nearly actinomorphic corolla and one nearly globose stigma. This combination of characters is shared by eight species and one variety of Petrocodon. The new taxon closely resembles P. luteoflorus (Fig. 2) in its pale-yellow corolla, two stamens, and divaricate thecae. However, it can be easily distinguished from the latter by the leaf blade being lanceolate or oblong (vs. narrowly elliptic or oblanceolate), lateral veins 2–3 (vs. 4–6) on each side of midrib, calyx segments 2.1–3.7 × 0.5–0.6 mm (vs. 6–8 × 1.5–2 mm) with entire (vs. entire to denticulate) margin, urceolate (vs. cannulate) corolla tube, abaxial corolla lip 0.8–1.1 mm (vs. 2–2.2 mm) long, and filaments 1.5–1.7 mm (vs. ca. 7 mm) long and straight (vs. S-shaped or geniculate near middle).

Figure 1. 

Petrocodon liboensis A habitat B, C flowering plant D adaxial and abaxial surfaces of leaf blade E cymes, and bracts (inset) F flower in front view G flower in side view H, I opened corolla J stamens, and anthers (inset) K pistil, and cross section of ovary (inset) L capsules, and seeds (inset) (Photographs by Sheng-Hu Tang).

Figure 2. 

Petrocodon luteoflorus A habitat B flowering plant C adaxial and abaxial surfaces of leaf blade D cymes, and bracts (inset) E flower in front view F flower in side view G calyx segments H opened corolla I stamens J pistil, and cross section of ovary (inset) K capsules L seeds (Photographs by Sheng-Hu Tang).

China. Guizhou Province: Libo County, Daqikong Scenic Spot, 25°16'N, 107°45'E, ca. 450 m elev., September 1, 2022, Sheng-Hu Tang 202209001 (holotype: CSH! CSH0192992; isotype: the Guizhou Botanical Garden!)

Herbs, perennial, stemless. Rhizome terete, 5–55 mm long, 3.9–6.5 mm in diameter. Leaves 8–30, basal or crowded at rhizome apex; petiole 8.2–32 mm long, 0.9–1.8 mm in diameter, short strigose; leaf blade lanceolate or oblong, 26.4–82 × 11.3–19 mm, chartaceous, adaxially sparsely short strigose, abaxially densely short strigose along veins, base cuneate or broadly cuneate, margin entire to dentate or slightly repand, apex acute; lateral veins 2–3 on each side of midrib, adaxially inconspicuous or slightly impressed, abaxially slightly prominent. Cymes 1–4, axillary, 2–7 flowers per cyme; peduncle 35.8–59.2 mm long, 0.9–1 mm in diameter, densely short strigose; bracts 3, free, margin slightly crenulate, outside short strigose, inside sparsely short strigose, central one linear-lanceolate, 4.2–4.5 × 0.6–0.8 mm, lateral ones oblanceolate, 5.9–7.3 × 1.3–2 mm; bracteoles 3, same indumentum and shape as bracts, and slightly smaller than bracts in size, 2.5–3 × 0.9–1.2 mm. Pedicel 2.8–9.3 mm long, 0.3–0.4 mm in diameter, densely short strigose. Calyx nearly actinomorphic, 5-parted from base; segments equal or subequal, 2.1–3.7 × 0.5–0.6 mm, linear, both outside and inside short strigose, margin entire. Corolla pale-yellow, 5.3–8 mm long, outside puberulent, inside glabrous, 5-parted to 1/5, segments slightly converged; tube urceolate, 4.5–6.9 mm long, 2.1–3 mm in diameter at base, 1.7–2.1 mm in diameter at mouth; limb indistinctly 2-lipped, adaxial lip 2-parted from base, segments triangular, equal, 0.5–0.8 × 0.9–1.2 mm, abaxial lip 3-parted from base, segments triangular, subequal, 0.8–1.1 × 1.5–1.7 mm. Stamens 2, adnate to abaxial side of corolla tube 2.8–3.1 mm above base, included; filaments 1.5–1.7 mm long, ca. 0.2 mm in diameter, straight, glabrous; anthers dorsifixed, coherent at apex, elliptic, 1.3–1.7 × 0.8–0.9 mm, glabrous; thecae divaricate, confluent at apex, dehiscing longitudinally; connective not projecting; staminodes 3, central one inconspicuous, adnate to adaxial side of corolla tube 1.6–2 mm above base, ca. 0.1 mm long, lateral ones conspicuous, adnate to adaxial side of corolla tube 2.3–2.5 mm above base, 0.7–0.8 mm long. Disc ring-like, pale yellow, 0.2–0.3 mm high, margin entire or repand. Pistil 7.9–12 mm long; ovary linear, 2.8–4.5 mm long, 0.5–0.6 mm in diameter, glabrous or short strigose, 1-loculed, placentas 2, parietal, projecting inward, 2-cleft; style 5.1–7.5 mm long, ca. 0.3 mm in diameter, glabrous or sparsely short strigose; stigma 1, terminal, nearly globose, undivided. Capsule straight, linear, 10.3–17.8 mm long, 0.8–0.9 mm in diameter, dehiscing loculicidally to base; valves 2, straight, not twisted. Seeds unappendaged, fusiform, 0.4–0.6 mm long.

Flowering occurs from late July to early September, and fruiting in the wild is unknown; only capsules from the previous year were observed.

The new taxon was named after its locality in Libo County, China.

The Chinese name is “Lì Bō Shí Shān Jù Tái” (荔波石山苣苔).

Only one population was found at the Daqikong Scenic Spot, Libo County, Guizhou Province, China. Plants were found growing on wet shady rocks in the valley, along with mosses, weeds, and shrubs.

Only one population of approximately 200 mature individuals was found in the type locality. It is highly likely that more populations were present in this area. Until further investigation, the species should be designated as “Data Deficient” (DD) according to the IUCN standards (IUCN 2022).

The new taxon is similar to eight species and one variety of Petrocodon in nearly actinomorphic flowers and one stigma. Its corolla tube is urceolate, similar to P. scopulorum (Chun) Yin Z. Wang (Chun 1946; Wang et al. 2011) and P. urceolatus F. Wen, H. F. Cen & L. F. Fu (Cen et al. 2017). The new taxon differs from P. scopulorum in its pale-yellow (vs. white) corolla, corolla parted to 1/5 (vs. 1/3), stamens 2 (vs. 4), and anthers coherent (vs. free). The new taxon is different from P. urceolatus by bracts 3 (vs. 2), pale-yellow (vs. white) corolla, puberulent (vs. glabrous) corolla outside, slightly constricted (vs. constricted) corolla mouth, and 1.7–2.1 mm (vs. ca. 0.9 mm) in diameter at corolla mouth. The new taxon was most similar to P. luteoflorus in terms of corolla color. The detailed morphological comparisons between P. liboensis and P. luteoflorus are presented in Table 1.