Aristolochia vuquangensis T.V.Do, 2021

Do, Truong Van, Nguyen, Hung Viet & Le, Khuong Duy, 2021, Aristolochia vuquangensis (Aristolochiaceae), a new species from Central Vietnam, Phytotaxa 500 (1), pp. 37-44 : 41-42

Aristolochia vuquangensis T.V.Do , sp. nov. ( Fig. 1 & Fig. 2 A-C)

The new species is most similar to A. wardiana J.S. Ma (1989: 348) and A. forrestiana J.S. Ma (1989: 321) by sharing an ovate to lanceolate-ovate leaf blade and a cylindric or saccate-shaped limb, but it differs principally from the two species in its densely brown hirsute outer surface of perianth (vs. pubescent in A. wardiana and glabrous to glabrescent in A. forrestiana ), oblong-ovate utricle, 1.1–1.5 cm long (vs. cylindric, 0.5–0.6 cm long in A. wardiana and cylindric, 0.8–0.9 cm long in A. forrestiana ), unequally semicircular 3-lobed limb in pre-anthesis with a revolute median lobe (vs. unlobed in A. wardiana and equally lanceolate 3-lobed limb with margin of all lobes not revolute in A. forrestiana ), abaxially the median lobe of limb concave (vs. not concave in both A. wardiana and A. forrestiana ), lower one-third of the inner surface of limb densely covered by trichomes (vs. entirely the inner surface of limb densely covered by processes in A. wardiana and densely covered by both processes and trichomes in A. forrestiana ).

Type: — VIETNAM. Ha Tinh province: Vu Quang district, Vu Quang National Park , elev. 1103 m, 18°15.133’N, 105°25.657’E, 30 August 2020, Do Van Truong DVT379 (holotype VNMN, isotypes HN, VNMN)

Perennial woody lianas, with oblong underground organs, 30–45 cm long, 3–5 cm in diam. Stem terete, young branches slender, zigzag, pubescent, turning to shallowly furrowed corky bark when mature, internodes 5–8 cm long. Petiole 2.2–2.7 cm long, slender, straight, pubescent. Leaf blade ovate to lanceolate-ovate, 8–13(–15) cm long, 3.5–6 cm wide, papery, base deeply cordate, sinus 6–7 cm deep, 3–5(–6) cm wide, apex acute, the adaxial surface dark green and glabrous, the abaxial surface puberulous, basal veins three, exceeding one-third the leaf length, secondary veins pinnate, six to seven pairs, venation reticulate, prominent on the abaxial surface, flattened on the adaxial surface, margin entire ( Fig. 1 B-C). Inflorescences cymose, 1–3-flowered, flowers clearly separated from each other, cymes on old woody stems, solitary or in a cluster of 3–4 ( Fig. 1 D-E). Inflorescence axis 1.5–2.2 cm long, straight, densely brown villous. Bracteoles clasping, subulate, 1.5–2 mm long, 1–1.5 mm wide, sessile, both sides densely brown pubescent, caducous ( Fig. 1D ). Pedicel 2–2.2 cm long, straight, densely brown pubescent. Ovary 1–1.5 cm long, 0.3–0.4 cm in diam., densely brown hirsute. Perianth strongly curved or horseshoe-shaped in lateral view, 3.5–4.2 cm high, greenishyellow to yellowish-brown, purple, outer surface densely brown hirsute. Utricle distinct from the tube, oblong-ovate, inflated, 1.1–1.5 cm long, 0.7–0.9 cm in diam., upper half of inner surface cream, lower half of inner surface pinkishpurple, and densely covered by trichomes ( Fig. 1J–I ). Lower part of tube horseshoe-shaped, constricted at its base, 4–5 mm diam., gradually inflated, 9–13 mm in diam., and upper part of tube cylindrically-shaped, much narrower than the lower part, 6–9 mm long, 4–6 mm in diam., inner surface of both parts dark-purple and smooth ( Fig. 1 J-I). Limb with three unequally semicircular lobes in pre-anthesis, the two lateral (upper) lobes smaller than the median (lower) lobe, 1.6–1.8 cm wide, 0.5–0.6 cm high, margin of all lobes somewhat curved, the median lobe 2.7–3 cm wide, 1.1–1.4 cm high, margin revolute and abaxially concave in ventral view, during anthesis forming a cylindric or saccate-shaped limb, 2.5–3.8 cm long, 1.5–2.1 cm diam., slightly constricted at apex, 1.2–1.7 cm diam., with erect margins, outer surface reddish-purple, inner surface dark-purple, with lower one-third densely covered by trichomes, and upper twothird smooth ( Fig. 1 D-H). Annulus present, dark-purple, 4–5 mm diam. Mouth 2.1–3 cm diam. Gynostemium 3-lobed, cylindrical, pale yellow, 3.5–4 mm high, 4–5 mm in diam., lobes with acute apices ( Fig. 1K ). Anthers oblong, 2–2.5 mm long, 0.5 mm wide, yellow. Capsule unknown.

Etymology: —The specific epithet refers to Vu Quang, a national park of Ha Tinh province, Central Vietnam, in which the new species was found.

Phenology: —Flowering was observed from April to May. Fruiting unknown.

Distribution and ecology: —The new species is currently known from Vu Quang National Park, Central Vietnam, located on the Truong Son mountain range on the Vietnam-Laos borderline. The new species grows on the humid and moist soils in subtropical broad-leaved evergreen forests, at elevations of ca. 1100 m, together with the dominant plants of Annonaceae (Fissigtima sp.), Celastraceae ( Euonymus nitidus Benth. (1842: 483)) , Ebenaceae ( Diospyros sp. ), Gesneriaceae (Rhaphiocarpus asper (Drake 1890: 127) B.L.Burtt (1997: 172)), Melastomataceae ( Kerriothyrsus tetrandrus (Nayar 1970: 42) C.Hansen (1998: 154)) , Primulaceae ( Ardisia sp. ), Rubiaceae ( Lasianthus sp. ), and Sapotaceae ( Eberhardtia tonkinensis Lecomte (1920: 346)) .

Conservation status: —Only one very small-sized population of A. vuquangensis was found in the restricted area (ca. 4 km 2) of Vu Quang National Park’s core zone, Ha Tinh province, Central Vietnam. Its natural habitat is well protected, but very few seedlings were recorded surrounding the mother plants or nearby. Furthermore, Vu Quang National Park is located on the eastern margin of the Vietnam-Laos borderline, where the weather in summers is hot and dry due to westerly winds and has been strongly affected by climate changes in recent years. Changes in precipitation and temperature across this area can shift, fragment, contract, or increase species’ ranges, leading to changes in Extent of Occurrence (EOO) and Areas of Occupancy (AOO), and the degree of fragmentation. These changes also expose organisms to conditions outside their range of physical tolerance, resulting in reduced survival and fecundity, leading to reductions in population size ( Deutsch et al. 2008). Thus, the persistence of the species might be at risk soon. The new species is preliminarily assessed as Critically Endangered (CR B2b, C1b, D) according to the IUCN category and criteria ( IUCN 2012, 2019). However, the lack of sufficient data about its natural distribution currently does not allow a final risk evaluation, and the species might be regarded as Data Deficient (DD). Further field surveys in surrounding areas (including protected forest areas in Laos) are needed to gain more information on its distribution.

Notes: — Aristolochia subgenus Siphisia , comprising 98 species and one subspecies, is distributed mainly in Southeast Asia and North and Central America ( González et al. 2014, Do et al. 2015). Morphologically, the new species is quite similar to some species of Aristolochia subgenus Siphisia such as Aristolochia cucurbitoides C.F. Liang (1975: 15) , A. forrestiana , A. melanocephala X.X.Zhu & J.S.Ma (2018: 298) , A. ovatifolia S.M. Hwang (1981: 226) , A. pseudoutriformis X.X.Zhu & J.S.Ma (2019b: 94) , A. thwaitesii J.D. Hooker (1856: 4918) , A. transeccta (Chatterjee 1948: 64) C.Y.Wu ex S.M. Hwang (1981: 231) , A. utriformis S.M. Hwang (1981: 228) , A. wardiana , A. yangii X.X.Zhu & J.S.Ma (2019b: 98) , and one recently described Isotrema species ( I. brevilimbum X.X.Zhu, Jun Wang & F.Cao (2020: 16)) by sharing a cylindric or saccate-shaped limb. The new species is most similar to A. forrestiana and A. wardiana by having an ovate to lanceolate-ovate leaf blade and a brown to reddish-purple, oblong-cylindric limb. However, it is easily distinguished from these two species by the combination of some morphological characters such as inflorescence, indumentum of perianth, shape and size of utricle, limb lobes, and indumentum of the inner surface of limb lobes. Detailed comparisons of the new species and its two similar species are shown in Table 1 and Figure 2 .

Figures

FIGURE 1. Aristolochia vuquangensis T.V.Do sp.nov. A. Underground organ; B. Abaxial leaf surface; C. Adaxial leaf surface; D. Solitary cyme showing a subulate bract (indicated by a white arrow); E. Cluster of two-three cymes on old woody stems; F. Ventral view of perianth showing a concave median limb lobe at abaxially (indicated by a white arrow); G. Top view of unequally semicircular 3-lobed limb in pre-anthesis showing revolute margin of the median lobe (indicated by a red arrow); H-I. Longitudinal section showing inner surface of perianth with a pinkish-purple and cream utricle (indicated by a red arrow), a smooth tube (indicated by blue arrows), and lower one-third of limb densely covered by trichomes (indicated by white arrows); J. Lateral view of perianth showing a strongly curved perianth and a cylindric or saccate-shaped limb; K. Close up of a 3-lobed gynostemium.All photographed by Do Van Truong.

FIGURE 2. Morphological comparison of Aristolochia vuquangensis T.V.Do sp.nov. with A. wardiana and A. forrestiana. (A- C. Aristolochia vuquangensis). A. Leaf shape; B. Perianth; C. Longitudinal section of perianth; (D-F. Aristolochia wardiana). D. Leaf shape; E. Perianth; F. Longitudinal section of perianth; (G-I. Aristolochia forrestiana). G. Leaf shape; H. Perianth; I. Longitudinal section of perianth. A-C photographed by Do Van Truong; D-F photographed by Xin Xin Zhu in Zhu et al. (2019a); G photographed by Cheng Liu & H, I photographed by Ji Dong Ya in Wang et al. (2020).