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Research Article
Isotrema putalengense, a new species of Aristolochiaceae from northern Vietnam and two new combinations in Isotrema
expand article infoQuoc Binh Nguyen, Hieu Cuong Nguyen§, Duc Binh Tran|, Phuong Hanh Nguyen|, Hong Truong Luu§
‡ Vietnam National Museum of Nature, Vietnam Academy of Science and Technology, Hanoi, Vietnam
§ Science and Graduate University of Science and Technology, Ho Chi Minh, Vietnam
| Institute of Ecology and Biological Resource, Vietnam Academy of Science and Technology, Hanoi, Vietnam
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Abstract

Isotrema putalengense Luu, Q.B.Nguyen & H.C.Nguyen is described as a new species from northern Vietnam. It looks most morphologically like I. wardianum but is distinguishable by a combination of different leafy and floral characters. Morphological comparison between the new plant and closest species is provided. In addition, combinations of two recently described Aristolochia species are made, namely Isotrema vuquangense (T.V.Do) Luu, Q.B.Nguyen & H.C.Nguyen and Isotrema yachangense (B.G.Huang, Yan Liu & Y.S.Huang) Luu, Q.B.Nguyen & H.C.Nguyen.

Keywords

Aristolochia, Isotrema vuquangense, Isotrema yachangense, Pu Ta Leng Mountain, Siphisia

Introduction

Isotrema Raf. (Aristolochiaceae) was recently resurrected as a genus independent from Aristolochia L. (Zhu et al. 2019a). Species of Isotrema are, in fact, those of Aristolochia subgenus Siphisia (Duch.) O.C.Schmidt (Schmidt 1935) and differ from others of Aristolochia by having strongly curved perianth, 3-lobed gynostemium, anthers paired on the outer surface of each gynostemium segment, and basipetally dehiscing capsule. This generic concept is followed in many later publications (Li et al. 2019; Zhou et al. 2019; Zhu et al. 2019b, c, d; Cai et al. 2020a; Wang et al. 2020a, b). Although several other authors still prefer assigning their newly described species under Aristolochia subgenus Siphisia (e.g., Cai et al. 2020b; Luo et al. 2020; Zhou et al. 2020; Do et al. 2021), of which Isotrema was accepted as one of the synonyms in the most recent nomenclatural review of Aristolochia-related taxa by Ohi-Toma and Murata (2016), the phylogenetic results by Zhu et al. (2019a) appear to be robust because of their extensive samples of Asian species and combination of molecular, chromosomic and morphological data. Therefore, Isotrema is followed in this paper.

To date, more than one hundred Isotrema species have been reported, including those named under Aristolochia (e.g., Liu and Deng 2009; Xu et al. 2011; Yao 2012; Huang et al. 2013; Wu et al. 2013; Do et al. 2014; Lu and Wang 2014; Nguyen et al. 2014; Ohi-Toma et al. 2014; Huang et al. 2015; Wu et al. 2015; Zhu et al. 2015; Do et al. 2016; Do et al. 2017; Do et al. 2018; Zhu et al. 2018; Zhou et al. 2019; Zhu et al. 2019a; Cai et al. 2020a, b; Do et al. 2021). Prior to this paper, 18 Isotrema species have been recorded for Vietnam (Lecomte 1909; Schmidt 1935; Pham-hoang 2000; Do et al. 2014; Do et al. 2015a, b; Do et al. 2016; Do et al. 2017; Do and Li 2018; Lai et al. 2019; Do et al. 2021).

During our botanical surveys in Pu Ta Leng Mountain, Lai Chau Province of northern Vietnam in 2020, we encountered a species that looks very much like I. wardianum (J.S.Ma) X.X.Zhu, S.Liao & J.S.Ma from China, India and Myanmar (Ma 1989; Zhu et al. 2019a; Wang et al. 2020b). After careful examination of the plant, we concluded it is a new species that is described here. Terminology follows Hou (1984) and Do et al. (2015a).

Taxonomy treatments

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 SH992 (holotype, VNMN!; isotypes, SGN!, VNMN!).

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 SH992 at the type locality.

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.

Table 1.

Morphological differences between Isotrema putalengense and close species (based on Hwang 1981; Ma 1989; Hwang et al. 2003; Zhu et al. 2019e; Wang et al. 2020b).

Characters I. putalengense I. ovatifolium I. pseudoutriforme I. utriforme I. wardianum
Petiole densely pubescent, 3–4.5 cm long villous, 3–5 cm long densely pubescent, 2–5 cm long glabrous, 4–8 cm long densely villous, 3–5 cm long
Lamina lanceolate to slightly pandurate, 15–20 × 4–6 cm, with auriculate base, adaxially sparsely pubescent, abaxially pubescent ovate, 5–13 × 4–8 cm, with cordate base, abaxially villous, adaxially glabrescent (densely villous when young) ovate to narrowly ovate, 10–22 × 7–13 cm, with cordate base, adaxially sparsely pubescent, abaxially densely pubescent ovate-lanceolate, 10–17 × 3–4 cm, with auriculate base, adaxially glabrous lanceolate, 12–16 × 3–4 cm, with auriculate base, adaxially subglabrous to glabrous
Pedicel 2.5–3 cm long 3–6 cm long 1.8–5 cm long 4–6 cm long 1–2.5 cm long
Bracteoles triangular, inserted on basal half of pedicel ovate, inserted on basal 1/2 of pedicel ovate, inserted on basal half and/or distal half of pedicel ovate-lanceolate, inserted above distal half of pedicel ovate, inserted on basal half of pedicel
Flower position on old woody stems axillary axillary, sometimes on stems axillary axillary
Perianth limb cylindric, ovoid in front view, straightly extended from upper tube, purple, 2.5–2.7 cm long × 1.2–1.3 cm in diameter, abaxially densely yellowish to brown hirsute subcylindric, straightly extended from upper tube, purple-red, 1.5–2.5 cm long × 1–1.5 cm in diameter, abaxially densely off-white villous cylindric, forming obtuse angle with upper tuber, light yellow, 2–3 cm long × 1–1.7 cm in diameter, abaxially sparsely villous ovoid, straightly extended from upper tube, yellow-green, 1–2 cm long × ca. 1 cm in widest diameter, abaxially sparsely pilose to glabrous cylindric, oblong in front view, forming obtuse angle with upper tube, purple with yellow apex, ca. 2.5 cm long × 0.9 cm in diameter, abaxially densely yellow villous
Limb lobes wide triangle subrounded or nearly truncate triangle or wide triangle ovate-deltate wide triangle
Perianth throat ca. 3–4 mm wide ca. 2.5 mm wide ca. 6 mm wide ca. 1 mm wide ca. 2–3 mm wide
Utricle indistinct from lower tube, 7–8 mm in diameter, light yellow indistinct from lower tube, 3–5 mm in diameter, purple-red indistinct from lower tube, ca. 7–9 mm in diameter, light yellow indistinct from lower tube, 3–4 mm in diameter, yellow-green distinct from lower tube, 5 mm in diameter, light yellow
Tube notch U-shaped V-shaped U-shaped V-shaped V-shaped
Upper tube 6–7 mm long × 5–6 mm in diameter, purple ca. 3–5 mm long × 3–4 mm in diameter, purple-red 3–4 mm long × 6–8 mm in diameter, light yellow ca. 3–5 mm long × 5–6 mm in diameter, yellow-green ca. 10 mm long × 6 mm in diameter, purple
Annulus hemispherical flat ring-like, raised convex hemispherical
Stigma lobes truncate to slightly obtuse, irregularly toothed obtuse, entire round, entire obtuse, entire obtuse, entire

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 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.

Isotrema vuquangense (T.V.Do) Luu, Q.B.Nguyen & H.C.Nguyen, comb. nov.

Aristolochia vuquangensis T.V.Do. Phytotaxa 500 (1): 41. 2021.

Type

Vietnam. Ha Tinh Province: Vu Quang District, Vu Quang National Park, 1103 m elevation, 18°15.133'N, 105°25.657'E, 30 August 2020, Do Van Truong DVT379 (holotype VNMN; isotypes HN, VNMN).

Isotrema yachangense (B.G.Huang, Yan Liu & Y.S.Huang) Luu, Q.B.Nguyen & H.C.Nguyen, comb. nov.

Aristolochia yachangensis B.G.Huang, Yan Liu & Y.S.Huang. PhytoKeys 153: 51. 2020.

Type

China. Guangxi Zhuang Autonomous Region: Baise City, Leye County, Huaping Town, Zhongjing (Yachang Orchid National Nature Reserve), 24°49.367'N, 106°24.029'E, 1341 m elevation, 29 July 2019, Z.C. Lu et al. 20190729YC4141 (holotype: IBK; isotypes: IBK, GXMG).

Acknowledgements

This work is funded by Vietnam Academy of Science and Technology via project number VAST 04.02/20-21. The authors would like to thank Mr Doan Hoang Son, Mr Giang A Pao and the local Hmong team for field support. Drs Jin Shuang Ma and Xinxin Zhu are acknowledged for providing useful literature. We are grateful to three anonymous reviewers for their critical comments and kind suggestions that have helped improve the manuscript.

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