Primulina heterochroa (Gesneriaceae) is described and illustrated here. This new species morphologically resembles P. pungentisepala and P. minutimaculata, but it is easily distinguished from congeners by some qualitative and quantitative characters in leaf, bract, calyx, indumentum, corolla and inflorescence. The conservation status of P. heterochroa is assessed as Critically Endangered (CR) according to IUCN Red List categories and criteria.
Molecular studies have shown that some former groups of Old World Gesneriaceae were artificial and unnatural (Li & Wang 2007; Möller & al. 2011; Wang & al. 2011; Weber & al. 2011; Möller & Clark 2013). For example, the previously recognized as unispecific genus Primulina Hance has been enlarged to some 163 species not only by the description of new species but also by the inclusion of all species of Chirita sect. Gibbosaccus C. B. Clarke and Chiritopsis W. T. Wang, as well as Wentsaiboea luochengensis Yan Liu & W. B. Xu and W. renifolia D. Fang & D. H. Qin (Wang & al. 2011; Weber & al. 2011; Xu & al. 2012; see also IPNI 2015+). The limestone areas of SW and S China and N Vietnam possess the highest biodiversity and differentiation of Primulina (Wei & al. 2010). As previously mentioned in many monographs and other literature (Wang & al. 1990, 1998; Hong & al. 2012; Wu & al. 2012; Wen & al. 2012; Zhao & al. 2013; Li & al. 2014; Zheng & Deng 2014), most species of this redefined genus have a narrowly restricted distribution, e.g. they often occur in only one or two limestone caves, sinkholes or small gorges. As a result of further exploring and study, some of these special and unique habitats are now better understood (Xu 2007). Many new taxa of Primulina have been reported in recent years, such as P. bullata S. N. Lu & Fang Wen (Lu & al. 2013), P. carinata Y. G. Wei, F. Wen & H. Z. Lü (Wen & al. 2014), P. crassirhizoma F. Wen, Bo Zhao & Xin Hong (Zhao & al. 2013), P. diffusa X. Hong, F. Wen, & S. B. Zhou (Zhou & al. 2014), P. leprosa (Yan Liu & W. B. Xu) W. B. Xu & K. F. Chung (Xu & al. 2010, under Chirita; Xu & al. 2012), P. ningmingensis (Yan Liu & W. H. Wu) W. B. Xu & K. F. Chung (Wu & al. 2011, under Chirita; Xu & al. 2012) and P. sinovietnamica W. H. Wu & Q. Zhang (Wu & al. 2012).
In 2008, we collected some living Primulina-like plants when we visited a local Chinese medicine market in Pingxiang, Guangxi, China. At first, we considered them to be P. pungentisepala (W. T. Wang) Mich. Möller & A. Weber (Weitzman & al. 1997, under Chirita; Weber & al. 2011) or P. minutimaculata (D. Fang & W. T. Wang) Yin Z. Wang (Wang 1981, under Chirita; Wang & al. 2011). However, when the plants flowered, the colour and morphology of the flowers really shocked us: the purplish brown and dark yellow bicoloured corolla had never been found in the genus Primulina before. The plants seemed to be a new and unique species. We tried to find the natural habitat of the plants and, fortunately, during a limestone flora survey in 2013, we found by chance a small natural population with fewer than 25 individuals near the Sino-Vietnam border in Pingxiang, Guangxi. After a thorough examination of herbarium material and relevant literature (Wang 1985; Wang & al. 1990, 1998; Li & Wang 2004; Wei & al. 2010; Wang & al. 2011; Weber & al. 2011), we have determined that this is a new species of Primulina. It is described, illustrated and compared with the morphologically similar P. pungentisepala and P. minutimaculata.
Material and methods
An overview of the genus Primulina from S and SW China and adjacent areas of Vietnam was prepared. All available specimens of Primulina stored in the following herbaria in China, Vietnam, the United States and the United Kingdom were examined (codes according to Thiers 2015+): ANU, BJFC, CDBI, CTC, E, HGAS, HIB, HN, IBK, IBSC, K, KUN, MO, PE, SZ, VNMN; as was material of Primulina from recent field work by the current authors in SW and S China and living material cultivated at the Gesneriad Conservation Center of China. All morphological characters were studied under dissecting microscopes, and are described using the terminology presented by Wang & al. (1990, 1998).
Results and Discussion
Holotype: China, Guangxi Zhuang Autonomous Region. Pingxiang city, Baiyun town, Jiaoguo village, near SinoVietnam border, 22.255854°N, 106.716474°E, 150 m, on moist tufa and rocky surface of limestone cliff, 22 Jul 2013, F. Wen, B. D. Lai & F.Y Nong 20130722-01 (IBK!; isotype: IBK!).
Diagnosis — Primulina heterochroa F. Wen & B. D. Lai differs from its congeners, P. pungentisepala (W. T. Wang) Mich. Möller & A. Weber and P. minutimaculata (D. Fang & W. T. Wang) Yin Z. Wang, by the following combination of characters: peduncle densely covered with spreading reddish purple eglandular and glandular hairs; bracts purple, outside reddish brown pubescent, inside densely purple glandular pubescent; calyx lobes outside densely spreading purple pubescent, inside sparsely shortly pubescent; corolla outside dark reddish purple to purplish brown, densely reddish purple pubescent, lobes inside dark yellow or bronzed yellow with dark brown longitudinal stripes (see also Table 1).
Description — Herbs perennial. Rhizome cylindric, 4–6 cm long, 1–1.5 cm in diam. Leaves 15–18, basal; petiole compressed, 3–4.5 × 0.6–0.8 cm, sparsely shortly strigose; leaf blade dark green with silvery lateral veins, narrowly oblong to oblong-elliptic, 6–10 × 3.5–4 cm, slightly fleshy, thickly chartaceous when dried, lower surface densely strigose and appressed pubescent, upper surface densely appressed pubescent, base attenuate to cuneate, margin entire, apex acute; lateral veins 4 or 5 on each side of midrib, slightly prominent on lower surface, inconspicuously sunken on upper surface. Cymes 5 or more, axillary, 3–5(–12)-flowered or more; peduncle brown, 8–15 cm long, c. 2.5 mm in diam., densely covered with spreading reddish purple eglandular and glandular hairs; bracts 2, opposite, purple, slightly rhombic to broadly lanceolate, 12–15 × 5–6 mm, persistent at flowering, occasionally withered; outside reddish brown pubescent, inside densely purple glandular pubescent, margin entire, apex acute. Calyx 5-parted to base; lobes lanceolate, c. 7 × 2 mm, nearly equal, outside densely spreading purple pubescent, inside sparsely shortly pubescent, margin entire, apex acute. Corolla outside dark reddish purple to purplish brown, throat with 2 bright yellow stripes, upper portion of inside corolla surface with 2 dark purple swollen sparsely short glandular hairy lines, inside of lobes dark yellow or bronzed yellow with dark brown longitudinal stripes, corolla c. 3 cm long, outside densely reddish purple pubescent, inside nearly glabrous; tube nearly tubular, c. 2 cm long, orifice c. 1.1 cm in diam.; limb distinctly 2-lipped; upper lip 2-lobed, lobes triangular, c. 6 mm long; lower lip 3-lobed, lobes oblong, c. 9 mm long, lobe mid-portion often twisted or constricted. Stamens 2, inserted c. 1.5 cm above corolla base; filaments dark purple, c. 6 mm long, geniculate c. 2 mm above insertion, pubescent just below anthers, otherwise glabrous; anthers reniform, constricted at middle, c. 2.5 mm long; staminodes 3, lateral ones inserted 9–10 mm above corolla base, reddish purple, linear, c. 6 mm long, glabrous, apex small capitate, central staminode inserted c. 6 mm above corolla base, punctiform, c. 0.5 mm long. Disk annular, c. 0.6 mm high; pistil c. 2.2 cm long (boundary of ovary and style ambiguous), densely covered with dark purple eglandular and glandular hairs; stigma 2-lobed, c. 3 mm long. Fruit not seen.
Phenology — Flowering specimens were collected in July; the fruiting time is unknown.
Distribution — Primulina heterochroa is known only from a single population at the type locality in Pingxiang city, SW Guangxi Zhuang Autonomous Region, S China, near the border with Vietnam (Fig. 4). It might be eventually discovered in the adjacent county of Longzhou and in Vietnam.
Ecology — Primulina heterochroa grows on shaded moist tufa of limestone cliffs under northern tropical limestone seasonal rain forest on the N-facing slope of a limestone hill at an altitude of about 150 m. The average annual temperature of Pingxiang is 21°C, the average annual precipitation is c. 1400 mm. Dominant plants at the type locality belong to Apocynaceae, Begoniaceae, Euphorbiaceae, Lauraceae, Moraceae, Rubiaceae and Urticaceae.
Conservation status and provisional Red List category — The new species is known only from one population with fewer than 50 mature individuals. We could not find a second population or any individual plants around the type locality despite careful field explorations on five occasions over the past several years. We therefore assess that Primulina heterochroa should be provisionally considered as Critically Endangered: CR B lab(ii,iii,v)+2ab(ii,iii,v); D, according to IUCN Red List categories and criteria (IUCN 2012).
Etymology — The specific epithet “heterochroa” is a Greek-derived compound adjective meaning different-coloured, referring to the remarkable contrasting colours of the corolla.
Vernacular name — Chinese: (yì sè bào chūn j tái). The first two characters mean “different colour” and thus mirror the specific epithet in referring to the corolla colours. The last four characters are the Chinese name for the genus Primulina.
Remarks — Several characters place this new species in the genus Primulina, e.g. stamens 2, stigma 1, capsule linear, straight, significantly longer than the persistent calyx lobes. Primulina heterochroa is very similar to P. pungentisepala and P. minutimaculata from a morphological point of view, but it can be distinguished from the latter two species by certain qualitative and quantitative characters in leaf, inflorescence, bract, calyx, corolla, hairs, etc. The three species share some similar characteristics, e.g. thicker and nearly fleshy leaf blades with silvery lateral veins, and thick pubescent hairs on the peduncles and pedicels. This hints at convergent evolution in three different species adapting to the subtropical monsoon climate with warm year-round temperatures and obviously alternating dry and wet seasons. The morphological differences between the three species are itemized in Table 1 and illustrated in Fig. 3.
Many new taxa of Primulina have been discovered, described and published recently, including this new one. We now know that the biodiversity of Primulina in limestone areas is very dependent on specialized habitats, such as caves, cliffs, crags, overhanging rocks, crevices, damp tufa, and so on, which are on a calcium-rich substrate further enriched from the weathering of the limestone. In exploring for plants in the past, the above-mentioned localities were usually ignored. Thus we expect additional undescribed taxa to be discovered in future field investigations.
Morphological comparison of Primulina heterochroa, P. pungentisepala and P. minutimaculata.
We thank Mr Fu-Yang Nong for collecting specimens and living plants and Mr Stephen Maciejeswki (Philadelphia, U.S.A.) for checking and revising the manuscript. This study was financially supported by the Guangxi Forest Science & Technology Foundation (Gui Lin Ke Zi  No.27), the Guangxi Natural Science Foundation (2013GXNSFAA019071), the Science Research Foundation of Guangxi Academy of Sciences (No. 12YJ25ZW013) and the International S & T Cooperation Projects of Guangxi (Guikehe 1347004-4) and Guilin (20130412). We also thank two anonymous reviewers for their comments on an earlier draft of this paper.