Petrocodon rubrostriatus K.Tan, X.Q.Song & M.X.Ren, 2023

Tan, Ke, Chen, Di-Ya, Song, Xi-Qiang & Ren, Ming-Xun, 2023, A new lithophilous species of Gesneriaceae, Petrocodon rubrostriatus, from the karst area of South Yunnan, China, PhytoKeys 230, pp. 289-299 : 289

Petrocodon rubrostriatus K.Tan, X.Q.Song & M.X.Ren sp. nov.

Fig. 2

Diagnosis.

The new species resembles Petrocodon mollifolius (W.T.Wang) A.Weber & Mich. Möller in leaf blade shape and size, flower base colour and size (Figs 2 , 3 ), but can be easily distinguished from the latter by corolla lobes with red to brownish longitudinal stripes (vs. corolla purely yellow), shorter lanceolate bracts, ca. 4.5 mm long (vs. linear, 12-20 mm long); longer style length ca. 10 mm (vs. 6-8 mm), and staminode insertion at 2.5-3 mm from corolla base (vs. inserted at the corolla base).

Type.

China. Yunnan Province: Lvchun county, Banpo township, Emaluoba community, 22°36'N, 102°16'E, altitude ca. 390 m, August 13, 2020, Ke Tan 20TK0811008 (Holotype: IBK! IBK00449896; Isotypes: HUTB, IBK! IBK00449897)

Description.

Perennial herb. Rhizomatous stem 1-2 cm long, 5-8 mm in diam., sometimes inconspicuous. Roots fibrous, numerous, pale brown to brown. Leaves in a densely crowded basal rosette, (6-)9-12; petioles 1.5-4 cm long, densely whitish villous; lamina adaxial surface dark green, abaxial surface green, both surfaces whitish pubescent, herbaceous, elliptic, broadly elliptic to ovate, or rhombic ovate, 5.5-11.5 × 2.3-3.5 cm, margin serrate; 4-5 pairs of lateral veins on each side, ascending, tertiary venation also distinctive; apex acute, occasionally obtuse, base cuneate, occasionally asymmetric. Inflorescences 1-4 per plant, axillary, cymose, 3-5-flowered; peduncles green to pale brownish green, puberulent, interspersed with a few longer hairs, 6.5-8.5 cm long; bracts 2, opposite, green to pale green, lanceolate, ca. 4.5 mm long, ca. 1 mm across at base, abaxially pubescent, adaxially nearly glabrous, margin entire; bracteoles 2, opposite, narrowly triangular, colour and hairs same as bracts; pedicels 8-12 mm long, ca. 1 mm in diam., hairs same as peduncle. Calyx 5-sect to base, lobes green to pale green, lanceolate, ca. 2.5 × 0.5 mm, abaxially pubescent, adaxially nearly glabrous, margin entire. Corolla pale yellow to bright yellow, 1.9-2.2 cm long, base near-spherical, outside pubescent interspersed with few glandular hairs, inside glabrous; tube infundibuliform, tubular at the base and widening around the middle, ca. 15 mm long, ca. 4 mm in diam. at the base, ca. 7.5 mm in diam. at orifice, abaxial lip much longer than adaxial lip, adaxial lip 2-lobed to near base, slightly obliquely semicircular, lobes ca. 8 mm long, ca. 6 mm wide at base, margin entire, apex rounded, each lobe with two to three red to brownish-red longitudinal stripes, abaxial lip 3-lobed to more than middle, elliptical, lateral ones slightly oblique and smaller than the central one, lobes ca. 13 mm long, ca. 5 mm wide at base, margin entire, apex rounded, each lobe with one red to brownish-red longitudinal stripe. Stamens 2, inserted in tube ca. 6 mm from corolla base; filaments pale green, ca. 8 mm long, straight, sparsely eglandular and glandular puberulent from the middle to the top and with glands from the middle to the bottom; anthers pale brownish yellow, elliptic, ca. 1.5 × 2.2 mm, glabrous, cohering face to face; staminodes 3, inserted 2.5-3 mm from corolla base, ca. 2 mm long, glabrous. Disc brownish green, ca. 0.9 mm high, glabrous, margin sinuate. Pistil ca. 21 mm long; ovary pale green, densely puberulent, ca. 10 mm long, ca. 1 mm wide; style whitish green, ca. 10 mm long, sparsely eglandular pubescent; stigma pale green, ca. 1 mm long, ca. 0.7 mm wide, disc-like. Capsule cylindrical, green when young, 1.7-2.1 cm long, ca. 1.5 mm wide, pubescent, becoming grey-brown and dehiscing into four valves when mature. Seeds unappendaged, long ellipsoid, ca. 0.4 mm long, ca. 0.2 mm wide.

Phenology.

Flowering in August, fruiting from October to November based on field observations.

Etymology.

The name Petrocodon rubrostriatus refers to the bright red to brownish stripes in the yellow corolla. This is noticeably different from the corolla colours of previously published Petrocodon species.

Vernacular name.

Hóng Wén Shí Shān Jù Tái (红纹石山苣苔). The first two words, “Hóng Wén”, mean red stripes of the corolla, and the following four words, “Shí Shān Jù Tái”, mean Petrocodon in Chinese.

Distribution and habitat.

Petrocodon rubrostriatus is only known from the type locality, near Lixianjiang river, Emaluoba community, Banpo township, Lvchun county, Yunnan. The species grows on moist, shady tufa surfaces of a limestone cliff in a monsoon rainforest at ca. 400 m. Thus, it is exposed to a warm environment with high air humidity in a moderately shaded monsoon rainforest.

Preliminary conservation assessment.

Petrocodon rubrostriatus is currently only known from the type locality in the Lixianjiang river basin, where only one small population was observed. In total in 2020, there were fewer than 300 mature individuals in five separate subpopulations, clustered together in a fairly small site of ca. 100 m2, on a moist cliff on the rock surface of an unnamed limestone hill close to the Lixianjiang river. The area of occupancy (AOO), is significantly smaller than the smallest AOO unit of IUCN (10 km2 for Critically Endangered under B2). In 2022, we revisited the type locality and observed a decline in habitat quality caused by a prolonged drought in Southwest China, and a reduction in mature plants to only about 100. This suggests that the new species is extremely vulnerable and easily disturbed by the persistent drought and also the activities of local people. According to the IUCN red list criteria ( IUCN 2022), the category of 'Critically Endangered’ [CR, B2a,b (iii,iv,v)] is proposed here.

Taxonomic notes.

The new species is morphologically similar to Petrocodon mollifolius , but most easily distinguished by the longitudinal stripes of red to brownish-red on the petal lobes. With the new species here, there are now 50 species and one variety in Petrocodon , and 47 species are distributed in China. South and Southwest China are the distribution and diversity centres of Petrocodon . The distribution pattern of a few species extends to the northern Indo-China Peninsula, namely P. coccineus (C.Y.Wu ex H.W.Li) Yin Z.Wang and P. hispidus (W.T.Wang) A.Weber & Mich. Möller which are both distributed in South China and Northern Vietnam ( Wei 2018; Wei et al. 2022), P. vietnamensis Z.B.Xin, T.V.Do & F.Wen is endemic of Vietnam ( Xin et al. 2021; Wei et al. 2022), P. bonii (Pellegr.) A.Weber & Mich. Möller is distributed from Thailand to Vietnam (GRC 2023, POWO 2023), and P. flavus D.J.Middleton & Sangvir. is an endemic of North Thailand ( Middleton et al. 2015). The new species is found in the karst region near the Lixianjiang river, the boundary of China with Vietnam and Laos, and thus, the new species may also extend to these countries. Currently, the new species is tentatively considered an endemic to China until detailed field investigations are carried out in its neigbouring countries.

Figures

Figure 2. Petrocodon rubrostriatus K. Tan, X. Q. Song & M. X. Ren, sp. nov. A habitat B habit C underside of plant D oblique side view of flower and buds E cyme F bracts and flower bud G dissected calyx lobes, pistil with opened corolla H front view of flower I side view of flower J stamens with coherent anthers K dehisced capsule (Photographs by D. C. Meng).

Figure 3. Petrocodon mollifolius (W. T. Wang) A. Weber & Mich. Moeller A adaxial view of flower B opened corolla with two fertile stamens and three staminodes C pistil with disc D dissected calyx lobes E stamens with coherent anthers (Photographs by D. C. Meng).