Isotrema plagiostomum X. X. Zhou & R. J. Wang, 2019

Zhou, Xin-Xin, Jiang, Guo-Bin, Zhu, Xin-Xin, Liu, Zi-Yue, Huang, Yi, Wang, Gang-Tao & Wang, Rui- Jiang, 2019, Isotrema plagiostomum (Aristolochiaceae), a new species from Guangdong, South China, Phytotaxa 405 (4), pp. 221-225 : 221-222

Isotrema plagiostomum X. X. Zhou & R. J. Wang , sp. nov., Fig. 1–2 .

Type: CHINA. Guangdong province, Yangchun city, Tanshui town, Fenglai village, 111°35’E, 22°5’N, alt. 76 m, 17 February 2019, flowers and young fruits, X. X. Zhou, Y. Huang, S. W. Yao & X. Zhou 5559 (holotype: IBSC 0831149, isotypes: IBSC 0831150, IBSC 0831151, IBSC 0831152, CSH 0164567).

Isotrema plagiostomum is similar to the sympatric I. thwaitesii in the appearance of obliquely truncated calyx limb in flowers, but differs in having woody liana (vs. erect subshrub) habit, cordate or auriculated (vs. attenuate to subcuneate) leaf base, axillary (vs. base of the stem or top of the rhizome) inflorescence position, and deeply (vs. shallowly) splitted calyx limb. A morphological comparison, as well as I. versicolor (S. M. Hwang) X.X. Zhu et al. ( Zhu et al., 2019: 15), is listed in detail ( Table 1).

Woody liana. Roots fusiform or globose. Stems terete, densely rusty villous at young twigs, glabrous when aged. Leaf blade oblanceolate or oblong-oblanceolate, 11.5–17.3 × 4–6.6 cm, acute to acuminate at apex, cordate, more or less obliquely auriculate at base, sinus 1–3 mm deep; green adaxially, pale abaxially; papery; almost glabrous, but only sparsely villous at midrib adaxially and abaxially, secondary veins pinnate, 7–11 each side; petiole ca. 1cm long, densely rusty villous. Inflorescence axillary. Flowers solitary to 3, fasciculate; pedicels ca. 1 cm long, usually pendulous, densely rusty villous; bracteoles 1–2, oval to lanceolate, 1–2 × 0.5–1 mm, densely rusty villous both sides, sessile. Perianth zygomorphic, densely rusty villous abaxially. Calyx tube geniculately curved, yellowish abaxially; basal portion of tube 2.2–2.8 cm long, with full to dotted purple on whitish surface, densely to sparsely tomentose adaxially; upper portion 1.2–1.7 cm long, with sparsely purple dots on yellowish surface, almost glabrous; limb subcylindric, 2.4–2.7 cm long, 1.2–1.5 cm in diam., obliquely truncated but deeply splitted,, adaxially villous and purple to yellowish from throat to mouth, abaxially purple to purplish; margin 3 dentate. Stamens 6 in 1 series, fully adnate in 3 pairs to the style column to form gynostemium , opposite to the stigma lobes; filaments absent; anthers oblong, ca. 2 mm long, extrorse. Gynostemium ca. 3.5 mm long, 2–2.5 mm in diam., fleshy; lobes 3, obtuse at apex; margin crisped; ovary inferior, cylindric, 4–6 mm long, 3–4 mm in diam., densely rusty villous abaxially. Capsule cylindric, 4–6.5 × 1.5–2 cm, 6-ribbed, sparsely villous, dehiscing basipetally. Seeds numerous, triangular ovate, 4–5 × 3–4 mm.

Figures

FIGURE 1. Isotrema plagiostomum X. X. Zhou & R. J. Wang. A. Habitat and habit, B. Stem with alternate leaves and axillary inflorescences, C. Adaxial (left) and abaxial (right) side of leaf, D. Inflorescence with fascicle flowers, E–G. Front, lateral and back view of flower, respectively, H–I. Longitudinal section of flower, showing changeable color and pubescence adaxially, J–K. Gynostemium and its transverse section, showing the paired anthers and their position, L–N. Capsule, and its transverse section, longitudinal section, respectively, showing the arrangement of seeds, O. Seeds.

FIGURE 2. Isotrema plagiostomum X. X. Zhou & R. J. Wang. A. Habit, showing alternate leaves and axillary inflorescences, B. Part of abaxial leaf surface, showing the pubescence, C. Front view of flower, showing the deeply “V-shaped” calyx limb, D. Longitudinal section of flower, E. Part of adaxial side of basal calyx tube, showing tomentose surface, F. Gynostemium, G. Capsule, H. Seeds. Illustrated by Bing-Mou WANG.