Isotrema putalengense Luu, Q.B.Nguyen & H.C.Nguyen, 2022

Nguyen, Quoc Binh, Nguyen, Hieu Cuong, Tran, Duc Binh, Nguyen, Phuong Hanh & Luu, Hong Truong, 2022, Isotrema putalengense, a new species of Aristolochiaceae from northern Vietnam and two new combinations in Isotrema, PhytoKeys 197, pp. 71-79 : 71

Isotrema putalengense Luu, Q.B.Nguyen & H.C.Nguyen sp. nov.

Fig. 1

Type.

Vietnam. Lai Chau Province, Tam Duong District, Pu Ta Leng Mountain , 22°27'17"N, 103°33'07"E, 2329 m elevation, 14 June 2020, Nguyen Quoc Binh, Tran Duc Binh, Doan Hoang Son, Nguyen Hieu Cuong SH 992 (holotype, VNMN!; isotypes, SGN!, VNMN!) .

Diagnosis.

The new species is most morphologically similar to I. wardianum in the shape of leaves and flowers but differs in having densely brown villous (vs. abaxially light brown villous) bracteoles, flowers on old woody stems (vs. in axils of leafy shoots), basally truncate perianth limb that is ovoid in front view and with purple apex (vs. basally obtuse, oblong in front view and with yellow apex), indistinct (vs. distinct) utricle from lower tube, U-shaped (vs. V-shaped) tube notch and internally black purple (vs. purple) tube.

Description.

Liana perennial, woody. Stems terete, pubescent. Petioles 3-4.5 cm long, densely pubescent; laminas lanceolate to slightly pandurate, 15-20 × 4-6 cm, adaxially sparsely pubescent, abaxially pubescent, margin entire, base auriculate, apex acute; veins palmate, 1 pair from base, lateral veins 3-4-paired; venation slightly adaxially sunken, abaxially prominent. Flowers on old woody stems, solitary; pedicel 2.5-3 cm, densely brown villous; bracteole inserted on basal half of pedicel, triangular, 5-5.5 mm long, 4-5.5 mm wide at base, densely brown villous, persistent. Ovary yellowish, 1.8-2.1 cm, 0.3-0.4 cm in diameter, densely brown villous, 6-ridged. Perianth horseshoe-shaped (in lateral view), 4-4.5 cm high, yellowish to purple, outside densely yellowish to brown hirsute with parallel veins, inside dark purple. Utricle indistinct from the tube, cylindrical, 7-9 mm long, 7-8 mm in diameter, outside light yellow, inside pilose and dark purple. Tube 3.5-4.0 cm, horseshoe-shaped, folded upwards at its middle forming a U-shaped notch, inside glabrous; lower tube 1.7-1.9 cm high and 0.6-0.7 cm in diameter, basally light yellow, apically purple; upper tube 0.6-0.7 cm long and 0.5-0.6 cm in diameter, parallel to the utricle, slightly constricted at the middle, purple; limb cylindric, ovoid in front view, curved forward, with truncate base, 2.5-2.7 cm long × 1.2-1.3 cm in diameter, inside dark red with dense dark-purple papillae, 3-lobed; lobes widely triangular, 0.5-1.3 mm high × 2-4 mm wide; throat ca. 3-4 mm high × 2 mm wide; annulus hemispherical, 0.5-0.6 cm high × 0.6-0.7 cm in diameter at base. Anthers 6, oblong, 2-2.2 mm long, adnate in 3 pairs to base of gynostemium. Gynostemium 3.5-4 mm long × 3.5-4 mm in diameter, stipitate; stipe ca. 0.5 mm; stigma connate, slightly 3-lobed; lobes (in older state) irregularly toothed. Fruits not seen.

Phenology.

Flowering found in June, fruiting unknown.

Etymology.

The specific epithet refers to the type locality, Pu Ta Leng Mountain which is part of the Hoang Lien Son Mountain Range and located about 30 km northwest of Vietnam’s highest Mt. Fan Si Pan.

Common and vernacular names.

Putaleng’s pipevine (Vietnamese name: Phòng kỷ Pu Ta Leng).

Distribution and habitat.

The new species is currently only known from Pu Ta Leng Mountain (with its highest peak at 3.049 m elevation), Tam Duong District, Lai Chau Province. It grows on humid fertile soils under a closed broadleaved evergreen forest unexplored botanically. There is no data available on the forest cover of the mountain. Our preliminary notes indicate that this forest is dominated by the Fagaceae , Lauraceae , Theaceae , Ericaceae and Magnoliaceae that are common families on the Hoang Lien Son Mountain Range, which is geographically considered part of the southern extension of the Himalayas and phytogeographically located in the Sikang-Yunnan Province ( Averyanov et al. 2003).

Preliminary extinction risk assessment.

The plant was recorded in a small population with few scattered individuals in a presently unprotected large forest. It may be found in adjacent similar forests on the Hoang Lien Son Mountain Range. Given this fact, it is provisionally assigned as Data Deficient until more information is recorded ( IUCN 2012; IUCN Standards and Petitions Committee 2022).

Discussion.

Isotrema putalengense is most morphologically similar to I. wardianum but they have a number of differences as expressed in the diagnosis. Besides, the new species is also close to I. utriforme (S.M.Hwang) X.X.Zhu, S.Liao & J.S.Ma ( Hwang 1981; Zhu et al. 2019a) in the shape of leaves and flowers but the latter has glabrous and longer (4-8 cm) petiole, yellow-green flowers borne in axils of leafy shoots, ovate-lanceolate bracteoles inserted above middle of peduncle, short upper tube (3-4 mm), convex annulus, saccate limb with ovate-deltate and erect lobes. The shape of flowers in the new species looks like that in I. pseudoutriforme (X.X.Zhu & J.S.Ma) X.X.Zhu, Jun Wang & J.S.Ma and I. ovatifolium (S.M.Hwang) X.X.Zhu, S.Liao & J.S.Ma ( Hwang 1981; Zhu et al. 2019a, e) but I. pseudoutriforme has ovate to narrowly ovate leaves and plain light yellow flowers, uncurved limb forming obtuse angle with upper tuber and ring-like annulus and I. ovatifolium has ovate leaves and abaxially densely off-white villous, purple-red flowers in axils of leafy shoots. The key morphological differences between the new species and those closest species are presented in Table 1 .

The leaves of the new species resemble those of I. cucurbitoides (C.F.Liang) X.X.Zhu, S.Liao & J.S.Ma ( Liang 1975; Hwang et al. 2003; Zhu et al. 2019a) and I. yangii X.X.Zhu & J.S.Ma ( Zhu et al. 2019e; Wang et al. 2020a) but these two species are readily different in a number of characters: I. cucurbifoides has leaves with 7-10 pairs of lateral veins, brownish flowers in axils of leafy shoots, ovate bracteoles, geniculately curved tube, 20 mm long utricle and deeply lobed perianth limb straight extended from upper tube and with 5-7 mm long lanceolate-acuminate lobes while I. yangii has leaves with 6-15-pairs of lateral veins, yellowish-white perianth with distinct purple stripes, 25-35 mm long utricles, internally smooth and pinkish or ochre perianth limb that is deeply 3-lobed and straight extended from upper tube and 16-24 mm long limb lobes.

Notably, the notch at the bent perianth tube of I. putalengense is obviously U-shaped while it is quite properly V-shaped in the above compared species except I. pseudoutriforme where the U-shaped notch is much narrower than that in the new species. Our field observations provisionally indicate that the notch shape is stable in, and could be typical for, Isotrema species. This character is more representative on longitudinal dissection of the perianth tube. However, its value as a supplemental taxonomic character for species identification has not been paid attention to in former Isotrema studies and needs further examination.

New combinations for some species of Isotrema

As a result of their study, Zhu et al. (2019a) has already transferred almost all species of Aristolochia subgenus Aristolochia Siphisia to Isotrema . Another four combinations were made for later described species ( Wang et al. 2020a). Following this generic concept, here we propose new combinations for the other taxa of the subgenus that were described recently.

Figures

Figure 1. Isotrema putalengense Luu, Q. B. Nguyen & H. C. Nguyen A habit B leaf C leaf lamina, adaxial surface D leaf lamina, abaxial surface E flower, side view F flower, front view G bracteole H perianth, longitudinal dissection I utricle, inside J ovary, cross section K gynostemium, side view L stigma, view from above M stem, cross section. Photographs by Hieu Cuong Nguyen from SH 992 at the type locality.