Isotrema sanyaense R.T.Li, X.X.Zhu & Z.W.Wang, 2019

Li, Rongtao, Wang, Zhiwei, Wang, Jun, Zhu, Xinxin & Xu, Han, 2019, Isotrema sanyaense, a new species of Aristolochiaceae from Hainan, China, PhytoKeys 128, pp. 85-96 : 85

Isotrema sanyaense R.T.Li, X.X.Zhu & Z.W.Wang sp. nov. Figs 1 , 2 , 3

Diagnosis.

Isotrema sanyaense is most similar to I. ledongense (Han Xu, Y.D.Li & H.J.Yang) X.X.Zhu, S.Liao & J.S.Ma and I. jianfenglingense (Han Xu, Y.D.Li & H.Q.Chen) X.X.Zhu, S.Liao & J.S.Ma ( Zhu et al. 2019), but significantly differs in the following characters: cymes 1-5-flowered, in hanging clusters of 1 to numerous branches, the pedicel nearly equal in length to flower, upper calyx tube obviously longer than basal calyx tube, calyx limb discoid, yellow inside, with purple-red stripes and spots, about 13-18 mm in diameter, glabrous, the throat dark red without spots, 4-6 mm wide. A detailed morphological comparison among the three species is shown in Figure 4 and Table 1 .

Type.

CHINA. Hainan: Sanya City, Haitang District, Haitangwan Town, 18°17'22"N, 109°39'45"E, 332m a.s.l., 28 October 2017 (fl), X.X.Zhu & R.T.Li ZXX17105 (holotype: CSH-0146607!; isotype: CSH!, KUN!).

Description.

Woody liana. Young stems terete, densely villous, with yellow to brown trichomes, old branchlets glabrous, old stems leafless. Petioles 0.8-1.7 cm long, young ones densely villous, with yellow to brown trichomes mixed with a white pubescence; blades lanceolate or elliptic-lanceolate, entire, 9-14 × 3-6 cm, leathery, adaxially glabrous, abaxially villous, with sparse larger white appressed trichomes, mixed with shorter white pubescence, veins pinnate, 5 to 10 pairs, base shallowly cordate to cordate, sinus <2-3 mm deep, apex acute. Cymes lateral on old woody stems or axillary, 1-5-flowered, in hanging clusters of 1 to numerous branches, pedicels 1.1-2.6 cm long, densely villous, with yellow to brown trichomes; bracteoles ovate-lanceolate, ca. 0.2-0.4 × 0.4 mm, inserted at the basis of pedicel, adaxially glabrous, abaxially densely villous, with yellow to brown trichomes. Calyx horseshoe-shaped, externally white with purple-red stripes; abaxially densely villous, with yellow to brown trichomes; basal tube ca. 2.2 × 0.5 cm, inside dark purple, with white patches spaced in the middle; upper tube ca. 2.5 × 0.5 cm, white inside, getting dark red in upper portion; calyx limb discoid, ca. 13-18 mm in diameter, abaxially densely villous, with yellow to brown trichomes, the inner surface yellow with purple-red stripes and spots, glabrous; throat dark red, 4-6 mm wide. Anthers 6, oblong, ca. 2.2 mm long, adnate in 3 pairs to base of gynostemium, opposite to lobes, dehiscence longitudinal. Gynostemium ca. 5 mm long, 3-lobed, apex acute; ovary inferior, 6-loculed, abaxially densely villous, with yellow to brown trichomes; ovules numerous; placentation axillary. Capsule oblong-ellipsoid, ca. 5 × 2 cm, dehiscing basipetally. Seeds triangular-ovate, 4-5 × 3-4 mm.

Phenology.

Flowering specimens have been collected in October and in fruiting specimens in May.

Etymology.

The specific epithet is derived from the type locality, Sanya City, in Hainan island, China. The Chinese name is given as “三亚关木通”.

Distribution and habitat.

Isotrema sanyaense is currently known from Haitangwan Town, Haitang District, Sanya City, Hainan Province, China. It grows in lowland dry forests dominated by families including Euphorbiaceae , Fagaceae , Lauraceae , Myrtaceae , Arecaceae and Rubiaceae at elevations between 332-400 m.

Conservation status.

Isotrema sanyaense is only known from two populations in Sanya City, Hainan island, China, with fewer than 30 individuals seen at each site. Therefore, the new species is assigned a preliminary status of Vulnerable (VU D2) according to IUCN Red List Criteria ( IUCN 2012), indicating a population with a very restricted area of occupancy (typically less than 20 km2) or number of locations (typically five or fewer).

Additional specimens examined (paratypes).

CHINA. Hainan: Sanya City, Haitang District, Haitangwan Town, 18°17'24"N, 109°39'43"E, 400m a.s.l., 28 October 2017 (vegetative), X.X.Zhu & R.T.Li ZXX17106 (CSH); same location, 18°17'29"N, 109°39'46"E, 376m a.s.l., 21 May 2018 (fr), X.X.Zhu & J.Wang ZXX18075 (CSH, KUN).

Figures

Figure 1. Isotrema sanyaense R. T. Li, X. X. Zhu & Z. W. Wang, sp. nov. A flowering branch B leaf C flower (front view) D flower (lateral view) E opened flower (showing the inside structure) F anthers and gynostemium G fruit H seeds. Scale bars: 6 cm (B); 1 mm (C, D, E); 5 mm (F); 2 cm (G); 3 mm (H).

Figure 2. Isotrema sanyaense R. T. Li, X. X. Zhu & Z. W. Wang, sp. nov. A habit B leaves (adaxially and abaxially) C inflorescence D flower (lateral view) E opened flower (showing the inside structure) F anthers and gynostemium G fruit H seeds. Scale bars: 1 cm (B, C); 2 cm (D, E, G); 5 mm (F, H).

Figure 3. Holotype of Isotrema sanyaense R. T. Li, X. X. Zhu & Z. W. Wang, sp. nov. [CSH- 0146607]!.

Figure 4. A, B Isotrema sanyaense R. T. Li, X. X. Zhu & Z. W. Wang, sp. nov. A habit B flowers C, D I. jianfenglingense (Han Xu, Y. D. Li & H. Q. Chen) X. X. Zhu, S. Liao & J. S. Ma C habit D flowers E, F I. ledongense (Han Xu, Y. D. Li & H. J. Yang) X. X. Zhu, S. Liao & J. S. Ma E flowering branch F flower (front view).