Isotrema brevilimbum X.X.Zhu, Jun Wang & F.Cao, 2020

Wang, Jun, Ya, Ji-Dong, Liu, Cheng, Liu, Guang, Cao, Feng, Ma, Jin-Shuang & Zhu, Xin-Xin, 2020, Taxonomic studies on the genus Isotrema (Aristolochiaceae) from China: II. I. brevilimbum (Aristolochiaceae), a new species from Guizhou, China, PhytoKeys 152, pp. 15-25 : 15

Isotrema brevilimbum X.X.Zhu, Jun Wang & F.Cao sp. nov. Figures 1 , 2A-F , 3 , 4A-C , 5

Type.

China. Guizhou: Weining County, Jinzhong Town, 2226 m alt., 5 Aug 2018, X.X. Zhu et al. ZXX18217 (holotype: CSH-0172289!; isotypes: CSH!, KUN!).

Diagnosis.

Isotrema brevilimbum is morphologically similar to I. ovatifolium (S.M. Hwang) X.X. Zhu, S. Liao & J.S. Ma and I. wardianum (J.S. Ma) X.X. Zhu, S. Liao & J.S. Ma, but differs from the former in its lamina long ovate (vs. lamina ovate in I. ovatifolium ), perianth limb forming right angle with upper tube, length nearly equal to width, and apex dark purple and opened (vs. limb straightly extended from upper tube, length significantly longer than width, and apex dark purple and constricted in I. ovatifolium ), differs from the latter in its lamina long ovate and abaxially densely villous (vs. lamina lanceolate and abaxially subglabrous or glabrous in I. wardianum ), perianth limb forming right angle with upper tube, length nearly equal to width, and apex dark purple and opened (vs. limb forming obtuse angle with upper tube, length significantly longer than width, and apex light yellow and constricted in I. wardianum ).

Description.

Climbing shrubs. Stems terete, densely villous when young, old branchlets glabrous. Petioles 1-4 cm long, densely villous; laminas long ovate, 5-13 × 2.5-3.5 cm, adaxially appressed villous, abaxially densely villous, base cordate, margin entire, apex acute; basal veins palmate, 2-3 pairs from base, lateral veins 4-6-paired. Flowers axillary or lateral on young stems, solitary, rarely paired. Pedicels pendulous, 1.5-3 cm long, densely villous; bracteole ovate, conduplicate, ca. 2 × 1 mm, abaxially densely villous, adaxially smooth, inserted on lower part of pedicel. Perianth tube geniculately curved, abaxially villous; basal tube ca. 1 cm long, inside dark red, upper tube ca. 1.5 cm long, inside red; limb short cylinder, length nearly equal to width, ca. 7 × 8 mm, forming right angle with upper tube, apex dark purple, opened, ca. 7 mm wide at mouth, inside dark red with densely tiny dark-purple papillae; throat subcircular, ca. 4 mm wide. Anthers 6, oblong, ca.1.5 mm long, adnate in 3 pairs to base of gynostemium, opposite to lobes. Gynostemium ca. 3 mm long, 3-lobed. Ovary terete, ca. 8 mm long, densely villous. Capsule cylindric, abaxially densely villous, ca. 4.5 × 2 cm. Seeds ovate, 4-5 × 3-3.5 mm, concave-convex.

Phenology.

Flowering from May to August, fruiting from July to September.

Etymology.

The specific epithet refers to the short cylinder perianth limb of the new species. The “brevi” means “short”, “limbum” means “limb”, so the new species is named Isotrema brevilimbum .

Common name (assigned here).

Duan Yan Guan Mu Tong (短檐关木通; Chinese name).

Distribution and habitat.

The new species is currently only known from Weining County of Guizhou, China. It grows by the roadside of farmland at an altitude of ca. 2200 m.

Preliminary conservation status.

Isotrema brevilimbum is known from a single population including two individuals on the roadside of farmland. The new species is assigned a preliminary status of vulnerable (VU) according to the IUCN Red List Categories ( IUCN 2012). However, since very few details exist about its natural distribution, the lack of sufficient data currently does not allow a final risk evaluation and the species might be regarded as data deficient (DD). Further field surveys in western Guizhou and northeastern Yunnan are needed to gain more information on its distribution. Not only is the area not under protection as a nature reserve, but also habitat disturbance brought about by human activities, such as grazing and farming, may have a negative impact on the new species.

Note.

Isotrema wardianum was previously only known from Myanmar and India. Sun and Zhou (2002) later reported the species from China, according to a specimen collected from Medog County of Tibet (H. Sun et al. 4935), but without flower or fruit. Nevertheless, the species had long been neglected by taxonomic studies of Huang et al. (2003), Do et al. (2015a), and Zhu et al. (2019a, 2019d) on Chinese Isotrema . It was not until 2018 that we discovered a seedling of Isotrema sp. at the same locality as that of H. Sun et al. 4935 and transplanted it in the nursery of the Kunming Institute of Botany. A year later, the plant grown from this seedling bloomed and enabled us to identify it as I. wardianum (Figs 2G-I , 4G-I ) and confirm its distribution in China.

Figures

Figure 1. Isotrema brevilimbum X. X. Zhu, Jun Wang & F. Cao. A Branch B leaf C, D flower E longitudinal-section of flower (showing inside structure) F anthers and gynostemium G capsule H seed. Drawn by S. Z. Qiao.

Figure 2. A-F Isotrema brevilimbum X. X. Zhu, Jun Wang & F. Cao. A Habitat B leaves C lateral view of flower D frontal view of flower E anthers and gynostemium F capsule G-I I. wardianum G habit H frontal view of flower I anthers and gynostemium. A Photographed by F. Cao B, E, F photographed by X. X. Zhu C, D photographed by G. Liu G photographed by C. Liu H, I photographed by J. D. Ya.

Figure 3. Holotype of Isotrema brevilimbum X. X. Zhu, Jun Wang & F. Cao (CSH- 0172289).

Figure 4. Leaves, lateral view of flowers, and longitudinal dissected flowers of Isotrema brevilimbum (A-C), I. ovatifolium (D-F), and I. wardianum (G-I). A-F Photographed by X. X. Zhu G photographed by C. Liu H, I photographed by J. D. Ya.

Figure 5. Distribution of Isotrema brevilimbum, I. ovatifolium, and I. wardianum based on field observation, specimens and literatures examined.