Chayamaritia vietnamensis, a new species from Son La Province, northern Vietnam, is described and illustrated. The phylogenetic study revealed that the new species is most closely related to C. banksiae and C. smitinandii. The morphological comparison suggests it as the third new species of Chayamaritia and distinguished from C. banksiae and C. smitinandii by a combination of morphological characters of leaf blades, bracts, calyx and corolla, especially its peltate leaf blades. This species is provisionally assessed as endangered (EN B1ab(iii), B2ab(iii)) using IUCN Categories and Criteria. Information on ecology, phenology and an identification key for the known Chayamaritia species are also provided.

Cliff-dwelling, Flora of Vietnam, new taxon, taxonomy

The genus Chayamaritia D.J.Middleton & Mich.Möller (Gesneriaceae) was originally established and described, based on molecular and morphological data (Middleton et al. 2015). The genus Chayamaritia comprises two species and is hitherto known only in Laos and Thailand. A thickened rhizomatous prostrate stem, along with alternately arranged leaves and the imbricate sepals characterise the genus (Middleton et al. 2015). The type species, Chayamaritia smitinandii (B.L.Burtt) D.J.Middleton, was initially placed in the genus Chirita Buch.-Ham. (Burtt, 2001), then transferred to the genus Henckelia Spreng. (Weber et al. 2011) and eventually separated as a new genus in 2015, together with the newly-described species, Chayamaritia banksiae D.J.Middleton (Middleton et al. 2015). Chayamaritia banksiae and C. smitinandii are endemic to Laos and Thailand, respectively (Middleton et al. 2015).

During a joint Sino-Vietnamese botanical survey for plant biodiversity in northern Vietnam in late October 2019, we collected an unknown Gesneriaceae plant. In the Xuan Nha Nature Reserve, Moc Chau District, Son La Province, northern Vietnam, we discovered this plant that looked like a Chayamaritia species. Detailed comparison of these specimens with the type specimens and protologues of known Chayamaritia species showed that these specimens neither fitted the existing protologues nor conformed to the type specimens of these species. Although, the leaf indumentum and inflorescence of the unknown plant was most similar to those of C. banksiae and C. smitinandii, it could be easily distinguished from the latter two by the combination of several morphological characters of the leaf blades, bracts, calyx and corolla, especially its peltate leaf blade. Thus, we confirmed that it represented a new species of Chayamaritia, which is the first Chayamaritia species from Vietnam. The description, illustration, information on ecology, phenology and provisional conservation assessment using IUCN (2019) of the proposed new species are provided. Furthermore, an identification key to the known Chayamaritia species is given.

The combined ITS and trnL-F matrix was 1,477 characters long (700 for ITS and 777 for trnL-F). Of the 378 variable characters, 155 (56.97%) were parsimony-informative. ML and BI analyses resulted in the same tree topology indicating the undescribed species as sister to the two known Chayamaritia species (BS = 97%, PP = 1), i.e. C. banksiae and C. smitinandii (Fig. 1).

Figure 1. 

Phylogenetic tree of Chayamaritia and related genera generated from the Maximum Likelihood analysis (ML) of the combined dataset (ITS and trnL-F). Numbers on the branches indicate bootstrap values (≥ 50%) of the ML and the posterior probability (≥ 0.5) of the BI analyses. Created by Long-Fei Fu.

Taxonomic treatment

Chayamaritia vietnamensis F.Wen, T.V.Do, Z.B.Xin & S.Maciej, sp. nov.

urn:lsid:ipni.org:names:77217099-1

Figs 2, 3C

Diagnosis

The new species can be easily distinguished from the known Chayamaritia species by its peltate leaf blades. Besides, it differs from C. banksiae by its leaf blades apex rounded and margin entire (vs. apex shortly acuminate and margin minutely dentate); bracts 3, apex rounded and margin entire (vs. 2, apex acuminate and margin dentate); calyx lobes inside glabrous and margin entire (vs. inside with white appressed hairs in upper half, margin coarsely dentate); corolla lobes margin entire (vs. margin being minutely dentate); lateral staminodes 2.5–4 mm long (vs. 5.5–11 mm long). It also differs from C. smitinandii by its leaf blades apex rounded and margin entire (vs. apex acuminate and margin minutely dentate); bracts 3, ovate narrow and apex rounded (vs. 2, narrowly elliptic to lanceolate, somewhat falcate, apex acuminate); calyx lobes inside glabrous and margin entire (vs. inside densely pubescent, margin slightly toothed or appearing as large sessile glands on margin).

Type

Vietnam. Son La Province: Moc Chau District, Xuan Nha Nature Reserve, 20°43'N, 104°40'E, elev. ca. 850 m, 31 October 2019, F. Wen, T.V. Do, Z.B. Xin & S. Maciejewski, VMN-CN1214 (Holotype: VNMN!; Isotypes: IBK!, VNMN!).

Description

Herbs perennial, rhizomatous prostrate thickened stem. Leaves basal, alternately arranged, numerous; petioles cylindrical, 10–25 cm long, 6–8 mm in diameter, densely covered with short white appressed hairs; leaf blade ovate to elliptic, peltate, 12–20 × 10–15 cm, 1.2–1.3 times as long as wide, both surfaces densely covered with short white appressed hairs, base rounded, apex rounded, margin entire; lateral veins 6–9 on each side of the mid-rib, impressed on the adaxial surface, prominent on the abaxial surface. Inflorescences cymose, all axes and bracts pale green with red appressed hairs; cymes 4–6, axillary, 1–3-branched, 2–12-flowered; peduncle 15–25 cm long, 4–6 mm in diameter, scattered villous; bracts 3, narrow ovate, 1.3–1.6 cm long, 5–6 mm wide, adaxially sparsely villous, abaxially densely villous, margin entire, apex rounded; pedicel 2.5–3.5 cm long, 1.5–2 mm in diameter, spreading puberulent. Calyx 5-parted nearly to the base, strongly imbricate; lobes ovate, ca. 1.3 cm long, ca. 6 mm wide, appressed villous outside, glabrous inside, margin entire, apex acuminate. Corolla 5.5–6.5 cm long, dark purple throughout outside, white to pale purple with two parallel yellow lines ventrally inside, lobes purple outside and inside, paler at base; tube 3.5–4 cm long, 1–1.2 cm in diameter at the mouth, 6–8 mm in diameter at the base; limb distinctly 2-lipped, adaxial lip 2-parted to over middle, lobes ca. 1 × 1 cm, orbicular; abaxial lip 3-parted to near the middle, lobes 1.3–1.5 × ca. 1 cm, oblong. Stamens 2, adnate to ca. 2.2 cm above the base of the corolla tube; filaments 1–1.2 cm long, white, sparsely pubescent, strongly geniculate at ca. 5 mm above the filament base, anthers ca. 2 mm long, sparsely pubescent. Staminodes 3, lateral ones 2.5–4 mm long, white, glabrous, adnate to 1.8 cm above the base of the corolla tube, the middle one ca. 0.5–1 mm long, adnate to 1.2 cm above the base of the corolla tube. Disc orbicular, ca. 3 mm in height, 5-crenate at the margin, glabrous. Pistil 4–4.5 cm long, ovary 2.5–2.8 cm long, 2–2.5 mm in diameter, mixed pubescent and glandular-pubescent; style 1–1.2 mm long, ca. 0.6 mm in diameter, mixed pubescent and glandular-pubescent; stigma only of lower lobe, bifid with blunt lobes, lobe ca. 3 mm long, ca. 0.5 mm in diameter. Capsules straight, 5.5–6.5 cm long, ca. 3.5–4 mm in diameter.

Figure 2. 

Chayamaritia vietnamensis F.Wen, T.V.Do, Z.B.Xin & S.Maciej A, B habitat C habit D adaxial (top) and abaxial (bottom) surface of leaf blade E cymes F peduncle G adaxial (top) and abaxial (bottom) surface of bracts H pistil, calyx and lateral view of corolla I opened corolla with stamens and staminodes J stamens with cohering anthers K pistil L adaxial (top) and abaxial (bottom) surface of calyx lobes. Photos by Fang Wen, arranged by Zi-Bing Xin.

Phenology

Flowering occurs from October to December and fruiting from November to January.

Etymology

The specific epithet “vietnamensis” is derived from Vietnam, which holds the first discovered and only known location for the species.

Figure 3. 

Three species of Chayamaritia A C. banksiae D.J.Middleton B C. smitinandii (B.L.Burtt) D.J.Middleton C C. vietnamensis F.Wen, T.V.Do, Z.B.Xin & S.Maciej. Photos by Fang Wen, arranged by Zi-Bing Xin.

Distribution and habitat

Chayamaritia vietnamensis is hitherto only known from the type locality, Xuan Nha Nature Reserve, Moc Chau District, Son La Province, northern Vietnam. It grows on rock surfaces surrounded by limestone areas in a subtropical evergreen seasonal rain forest.

Conservation status

Chayamaritia vietnamensis is known from two small-sized populations in the Xuan Nha Nature Reserve’s buffer zone. The EOO and AOO of the new species are about 6.15 km² and 2.2 km², respectively. Furthermore, the natural habitat is mostly disturbed by local farmers who impose intense pressure on the remaining primary forest patches, by converting the natural habitat of the species into cornfields. Thus, following the IUCN Red List Categories and Criteria (IUCN 2019), it is provisionally assessed as endangered (EN B1ab(iii), B2ab(iii))

From the viewpoint of morphology, the newly-described species should be treated as a species of Chayamaritia, because it exhibits a suite of morphological characters that are diagnostic to the genus and should not be established as a distinct genus. It has a thickened rhizomatous prostrate stem, alternately arranged leaves and imbricate sepals (Middleton et al. 2015). The current molecular work also confirmed that the new species is sister to a clade comprising the two known Chayamaritia species (C. banksiae and C. smitinandii). A detailed morphological comparison of the new species with its two relatives is summarised in Table 2. This new species is the first Chayamaritia species reported from Vietnam. In order to facilitate identification, we also provide an identification key to all known Chayamaritia species.

In the present study, we discovered and described a new species of Chayamaritia from Vietnam, based on both morphological and molecular evidence. This newly-described species further suggests floristic similarities amongst countries of the Indochinese Peninsula. Our new finding provides an essential addition to the ongoing project of ‘Flora of Vietnam’ and ‘Flora of Cambodia, Laos and Vietnam’.

We want to thank the staff from Xuan Nha Nature Reserve for guiding our investigation and collecting the specimens. We also want to thank Michael LoFurno, Adjunct Professor, Temple University, Philadelphia, USA, for his editorial assistance. This study was financially supported by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) (106.03-2019.308), the Foundation of Guangxi Key Laboratory of Plant Conservation and Restoration Ecology in Karst Terrain (19-050-6; 19-185-7), the National Natural Science Foundation (31860047), Guilin Science and Technology Foundation (20180107-6), the Key Science and Technology Research and Development Project of Guangxi (Guike AD20159091), Guangxi Natural Science Foundation (2020GXNSFBA297049), Basal Research Fund of GXIB (Guizhiye20009) and the 21^st Talent project of “Ten-Hundred-Thousand” in Guangxi.