Isotrema guangdongense Y.S.Chen & Y.C.Xu, 2023

Xu, Lian-Sheng, Li, Tian, Xu, Ye-Chun & Chen, You-Sheng, 2023, Isotrema guangdongense (Aristolochiaceae), a new species from Guangdong, South China, Phytotaxa 601 (1), pp. 71-80 : 74-79

Isotrema guangdongense Y.S.Chen & Y.C.Xu , sp. nov. ( Fig. 2 ).

Type: — CHINA. Guangdong: Guangzhou, Conghua District, Liangkou Town , Wuzhi Mountain Scenic Area , 113°47′7″E, 23°42′28″N, forests on mountain slopes, elev. 936 m, 3 April 2022, Y. S . Chen & Y. C . Xu 22018 (holotype IBSC0889722 ) .

Woody liana. Stems terete, densely rusty villous at young twigs, glabrous when aged. Petioles 7–10 cm long, young ones densely rusty villous; leaf blade cordate, entire, 25–30 × 20–25 cm, papery, adaxially puberulous or glabrous, abaxially densely rusty villous, veins palmate, 2 pairs from base, base cordate or auriculate, sinus 2–4 cm deep, apex acute to acuminate. Flowers usually solitary, axillary; pedicels 4–7 cm long, usually pendulous, densely rusty villous; bracteoles subulate, inserted at the basis of pedicel, densely rusty villous both sides, sessile. Perianth zygomorphic, densely yellow to brown villous abaxially. Calyx tube horseshoe-shaped, externally white with purple-red stripes; basal portion of tube 20–30 × 5–7 mm, with whitish surface, densely arachnoid tomentum adaxially; upper portion 20–30 × 4–5 mm, with yellowish surface, almost glabrous; throat of tube yellow, discoid-suborbicular or oval, 10–17 mm in diam; limb adaxially white with dense big purple spinous processes on whitish surface, distinctly 3-lobed, lobes triangular and apex acute, upper two lobes forming acute angle, abaxially pale white. 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. 3 mm long. Gynostemium ca. 6 mm long, 4–5 mm in diam., fleshy; lobes 3, obtuse at apex; margin crisped; ovary inferior, cylindric, 10–12 mm long, 4–5 cm in diam., densely rusty villous abaxially; ovules numerous; placentation axillary.

Phenology:—Flowering in April and fruiting in July to October.

Etymology:—The specific epithet is derived from the type locality, Guangdong Province, South China. The Chinese name is given as “ffiuẍ†®” (tu er guan mu tong).

Distribution and habitat:—Through checking numerous specimens and pictures, we found that Isotrema guangdongense is currently only known from Guangdong Province and Fujian Province, including Guangzhou City, Meizhou City, and Chaozhou City in Guangdong Province and Nanjing County in Fujian Province ( Fig. 3 ). It grows in evergreen broadleaved forests on stony mountain slopes at altitudes of 600–1000 m.

Conservation status:— Isotrema guangdongense is known from a few populations on stony mountain slopes in Guangzhou City, Meizhou City, and Chaozhou City in Guangdong, and Nanjing County in Fujian Province. One population from Guanghzou is in a scenic spot, but the plant number is very small. The two populations from Meizhou and Chaozhou have been severely damaged due to exploitation by human activities. In addition, most populations are outside of protected areas and local people continue to impose strong pressure on the remaining forest patches for medicinal plants, firewood, and converting the vegetation into tea plantation. Therefore, the new species is assigned a preliminary status of Vulnerable (VU D2) according to the IUCN red list categories and criteria ( IUCN Standards and Petitions Subcommittee 2019), indicating a population with a very restricted area of occupancy (typically less than 20 km 2) or number of locations (typically five or fewer).

Similar species and phylogenetic position:— Isotrema guangdongense belongs to Isotrema because its calyx strongly curved, gynostemium 3-lobed, anthers paired on the outer surface of each gynostemium segment, and capsule dehiscing basipetally. I. guangdongense is similar to I. kwangsiense ( Fig. 4 ) in its habit, terete stems, entire and cordate leaves, palmate veins, pendulous pedicels, calyx limb with irregularly dotted dark purple, horseshoe-shaped tube and yellow throat of calyx tube, but different by its leaf blade cordate, 25–30 × 20–25 cm (vs. cordate to orbicular, 11–13 × 9–32 cm), leaf apex acute to acuminate (vs. obtuse or acute), leaf indumentum adaxially puberulous or glabrous, abaxially densely rusty villous (vs. both surfaces moderately to densely hirsute), inflorescence usually solitary flowered, usually axillary on new stems (vs. racemes 2–3 flowered, usually on old stems), pedicel 4–7 cm long (vs. 2.5–3.5 cm long), calyx limb white with dense big purple spinous processes, abaxially pale white (vs. dark purple with dense big purple spinous processes, abaxially pale yellowish green), upper two lobes of calyx limb forming acute angle (vs. flat to obtuse angle), throat of calyx tube 10–17 mm in diam. (vs. 5–6 mm in diam.) and gynostemium ca. 6 mm long (vs. ca. 3 mm long) ( Fig. 5 ).

Through further in-depth study of more specimens, we found that I. kwangsiense is mainly distributed in southwestern Guangxi and Guizhou Province. According to Huang (1987) and ( Zhao 1991), Aristolochia kwangsiensis Chun & F. C. How ex C. F. Liang (= I. kwangsiense ) is also distributed in Guangdong and Fujian. But according to our analyses, the specimens usually identified as I. kwangsiense from Guangdong and Fujian were the misidentifications of I. guangdongense . In conclusion, I. kwangsiense is only distributed in Guangxi and Guizhou, but I. guangdongense is currently only known from Guangdong and Fujian. Therefore, the geographical distributions of these two species are different.

Isotrema guangdongense is also similar to I. austroszechuanicum (C. P. Tsien & C. Y. Cheng ex C. Y. Cheng & J. L. Wu 1987: 221) X. X. Zhu, S. Liao & J. S. Ma (2019a: 8) in its habit, terete stems, entire and cordate leaves, adaxially slightly villous, palmate veins, pendulous pedicels, and horseshoe-shaped tube, but distinguished by its white limb with dense big purple spinous processes (vs. yellowish green limb with dense, small purple warts, the pale yellowish green abaxial surface of the limb), throat of calyx tube yellow and 10–17 mm in diam. (vs. throat of calyx tube reddish brown and 6–9 mm in diam.).

Morphological differences among Isotrema guangdongense , I. kwangsiense and I. austroszechuanicum are shown in Table 2.

Additional specimens examined:— CHINA. Guangdong Province: Chaozhou, Chao ‘an District, Fenghuang Town, Fenghuang Mountain , elev. 950 m, 25 Nov. 2009, X. F. Zeng ZXF8781 ( CZH); ibid, elev. 940 m, 9 Apr. 2010, X. F. Zeng ZXF9242 ( CZH); ibid, 3 Jul. 2022, T. Li & X. F. Zeng LT20220703 ( IBSC); Meizhou, Meixian District, Yanyang Town , Yinna Mountain , Lingguang Temple, elev. 688 m, 1 Jul. 2022, T. Li & X. F. Zeng LT20220701 ( IBSC) .

Figures

FIGURE 2. Isotrema guangdongense.A. Habitat and habit; B. Stem with alternate leaves; C. Stems with densely rusty villous; D. Petioles; E. Leaf veins; F.Adaxial (left) and abaxial (right) side of leaf; G-I. Front and lateral view of flower, respectively; J-K. Longitudinal section of flower, showing changeable color and villous adaxially; L-M. Gynostemium, showing the paired anthers and their position. All photos were taken by You-Sheng Chen based on Y. S. Chen & Y. C. Xu 22018.

FIGURE 3. Distribution of Isotrema guangdongense (●) and I. kwangsiense (▲).

FIGURE 4. Living plants of Isotrema kwangsiense. A. Habitat and habit; B. Racemes; C. Adaxial (left) and abaxial (right) side of leaf; D-E. Front and lateral view of flower, respectively; F. Longitudinal section of flower, showing changeable color and villous adaxially; G. Gynostemium, showing the paired anthers and their position. All photos were taken by You-Sheng Chen based on plants cultivated in South China Botanical Garden.

FIGURE 5. Morphological comparison of Isotrema guangdongense and I. kwangsiense. A. Adaxial side of leaf (left: I. kwangsiense; right: I. guangdongense); B. Lateral view of flower (left: I. kwangsiense; right: I. guangdongense); C. Abaxial side of leaf (left: I. kwangsiense; right: I. guangdongense); D. Front view of flower (left: I. kwangsiense; right: I. guangdongense); E. Calyx limb throat (up: I. guangdongense; down: I. kwangsiense); F: Longitudinal section of flower (left: I. kwangsiense; right: I. guangdongense). Photos of I. guangdongense are all from Y. S. Chen & Y. C. Xu 22018, photos of I. kwangsiense are all from cultivated plants in South China Botanical Garden.All photos were taken by You-Sheng Chen.