Aristolochia laotica T.V.Do, 2023

Do, Truong Van, Hoang, Thao Thi, Wen, Fang, Wanke, Stefan, Forbes, Malcolm & Souladeth, Phetlasy, 2023, Aristolochia laotica (subgen. Siphisia), a new species from Northeastern Laos, Phytotaxa 591 (2), pp. 155-163 : 156-159

Aristolochia laotica T.V.Do , sp. nov. ( Figs. 1 , 2 & Fig. 3A–D )

The new species is most similar to A. vuquangensis T.V. Do (2021: 41) , a species endemic to Central Vietnam, from which it differs mainly by its leaf lamina oblanceolate to narrowly elliptic (vs. ovate to lanceolate-ovate), with truncate to shallowly cordate base (vs. deeply cordate) and pinnate veins (vs. palmate); its perianth sparsely brown hirsute to glabrescent (vs. densely brown hirsute), with the inner surface of utricle uniformly purple (vs. upper half cream and lower half pinkish-purple), and the limb lobes indistinct, straight and strongly inflated (vs. distinct with two somewhat revolute and curved lower lobes, deeply sunken between them) with inner surface thoroughly densely covered by trichomes and warts (vs. the lower third densely covered by trichomes and the upper two-thirds smooth).

Type: — LAOS. Xieng Khouang province: Phou Koud district , elev. 1193 m, 19°44‘49.4“N, 103°14‘45.6“E, 27 March 2022 (fl, fr), Forbes and Oudomsouk 01 (holotype FOF [FOF0005199]!, isotypes: FOF!, VNMN!)

Woody lianas reaching the canopy, more than 10 m high. Stems terete, young branches slender, straight, pubescent, turning to deeply furrowed corky bark when mature, internodes 3–5 cm long. Leaves crowded near the distal portions of the branches. Petiole 2.2–2.7 cm long, slender, straight, pubescent; leaf lamina oblanceolate to narrowly elliptic, 14–18 × 3.5–4.5 cm, papery, base truncate to shallowly cordate, apex acute, the adaxial surface dark green and glabrous, the abaxial surface puberulous, veins pinnate, eight to ten pairs, higher order venation reticulate, flattened on the adaxial surface, prominent on the abaxial surface, margin entire. Inflorescences 1–2-flowered cymes, formed on old woody stems, solitary or in a cluster of two-three cymes. Inflorescence axis 1.5–2 cm long, straight, purplish-brown, sparsely villous to glabrescent. Bracteoles clasping, subulate, 1.5–1.8 × 1–1.2 mm, sessile, caducous, densely brown pubescent on both sides. Pedicel 2.2–3.0 cm long, straight, sparsely villous to pubescent. Ovary narrowly cylindric, 2.2–2.5 cm long, 0.4–0.6 cm in diam., densely brown villous. Perianth horseshoe-shaped (in side view), 4.5–5.0 cm long, outside uniformly purple, sparsely brown hirsute to glabrescent, with conspicuous parallel veins or dots; utricle indistinct from the tube, oblong-ovate, inflated, 1.2–1.4 cm long, 0.8–1 cm in diam., inside with a uniformly purple band and densely pubescent; tube horseshoe-shaped, folded upwards at its middle; lower part of tube strongly inflated, 1–1.4 cm in diam., inner surface dark-purple, smooth, upper part of tube cylindrical, slightly constricted and narrower than the lower portion and the utricle, 1.5–1.8 cm long, 0.7–0.8 cm in diam., inner surface purple, smooth; limb cylindric or saccate-shaped, strongly inflated, much larger than the utricle and tube, 5–7 cm long, 2.8–3.2 cm diam., constricted at base and apex, forming a right angle with the upper tube, the three lobes indistinct and slightly asymmetric, almost connate, constricted at apex, entirely inside covered with dense trichomes and warts; annulus present, dark-purple, 0.9–1.1 cm diam.; throat dark-purple. Gynostemium 3-lobed, cylindrical, cream, 8–10 mm long, 7–8 mm in diam., lobes acute; anthers oblong, 5–6 mm long, 0.5 mm wide, yellow. Capsule cylindrical, 6–8 cm long, 2–2.5 cm in diam, 6-ridged, greenish-brown, glabrescent, basipetally dehiscent. Seeds ovoid, 7–8 mm long, 5–6 mm in diam, not winged, the adaxial surface deeply concave with a prominent, central, longitudinal, funiculus, the abaxial surface convex, both surfaces smooth.

Etymology: —The specific epithet is derived from the country, Laos, where the new species was found.

Phenology: —Flowering was observed from February to March, and fruiting from March to April.

Distribution and ecology: —The new species is currently known only from Phou Koud district, Xieng Khouang province, Northeastern Laos. The new species grows in moist and wet soils, and alongstream banks with very smooth and steep walls in subtropical broad-leaved evergreen forests, at elevations of ca. 1100–1250 m.

Conservation status: —At least three small-sized populations of Aristolochia laotica were found in the spirit forest areas in Phou Koud district, Xieng Khouang province, Northeastern Laos. The first population is distributed in an area of less than 8 km 2, the second in an area of less than 15 km 2, and the third in an area of less than 12 km 2. Estimated from the locations of these three populations, the Extent of Occurrence (EOO) is ca. 600 km 2 and the Area of Occupancy (AOO) is ca. 35 km 2. Furthermore, the habitats have been impacted by human activities, especially agricultural extension. Given this situation, the new species is provisionally assessed as Endangered (EN) (B1 + B2ab(iii, iv)), following the IUCN Red List Categories and Criteria ( IUCN 2012, 2019).

Notes: — Aristolochia laotica is morphologically similar to some species of A. subgen. Siphisia such as A. thwaitesii J.D. Hooker (1856: 4918) , A. cucurbitoides C.F. Liang (1975: 15) , A. transeccta (Chatterjee 1948: 64) C.Y.Wu ex S.M. Hwang (1981: 231) , A. utriformis S.M. Hwang (1981: 228) , A. ovatifolia S.M. Hwang (1981: 226) , A. forrestiana (1989: 321) , A. wardiana S.J. Ma (1989: 348) , A. melanocephala X.X.Zhu & J.S.Ma (2018: 298) , A. pseudoutriformis X.X.Zhu & J.S.Ma (2019: 94) , A. yangii X.X.Zhu & J.S.Ma (2019: 98) , A. vuquangensis T.V. Do (2021: 41) and two recently described species under the segregate genus Isotrema (i.e. I. brevilimbum X.X.Zhu, Jun Wang & F.Cao (2020: 16) and I. putalengense Luu, Q.B.Nguyen & H.C. Nguyen (2022: 72) . They all have a cylindric or saccate-shaped limb. Among them, the new species shows its highest resemblance with A. vuquangensis , by having 1–2-flowered cymes exclusively on old woody stems and purple perianth with a horseshoe-shaped tube and a strongly inflated, asymmetric limb, much larger than the utricle and tube. However, it is easily distinguished from the latter by the leaf shape and venation, the perianth indumentum, the inner surface indumentum and color of the utricle, the shape and indumentum of the limb lobes, and the size of the annulus. Detailed comparisons of the new species and its similar species are shown in Table 1 and Fig. 3 (A–H).

The new species is characterized by having an oblanceolate to narrowly elliptic leaf lamina with a shallowly cordate base and pinnate veins, which is similar to those of Aristolochia versicolor S.M. Hwang (1981: 224) , another species of Aristolochia subgenus Siphisia , recently recorded for the flora of Laos ( Le & Do 2022). However, it is easily distinguished from the latter by some floral traits such as the shape of the limb (cylindric or saccate-shaped vs. discoid or nearly round), the indumentum of inner surface of limb lobes (densely covered by trichomes and warts vs. smooth), and the colour of the throat (dark-purple vs. white) ( Fig. 3A–D; I–K ).

The new Aristolochi a species described here, together with the previously known seven congeneric species ( Le & Do 2022), increases the number of Aristolochia species occurring in the flora of Laos to eight, of which five belong to subgenus Aristolochia , and three to subgenus Siphisia . Here we provide an identification key to identify all the known species of the genus Aristolochia in the country.

Figures

FIGURE 1. Aristolochia laotica T.V.Do, sp.nov. A. Habitat; B. Mature stems; C. A branch bearing leaves; D. Adaxial and abaxial leaf surface; E. 2-flowered cyme on old woody stems; F. Two 1-flowered cymes on old woody stems. Photo credits, M. Forbes.

FIGURE 3. Comparison of morphological traits of Aristolochia laotica T.V.Do, sp.nov. with A. vuquangensis and A. versicolor. A– D. Aristolochia laotica. A. Leaf shape; B. Lateral view of perianth; C. Longitudinal section of perianth; D. Ventral view of perianth. E–H. A. vuquangensis. E. Leaf shape; F. Lateral view of perianth; G. Longitudinal section of perianth; H. Ventral view of perianth. I– K. Aristolochia versicolor. I. Leaf shape; J. Longitudinal section of perianth; K. Frontal and dorsal view of perianth. Photo credits, A–D, M. Forbes; E–K, Do Van Truong.

FIGURE2.AristolochialaoticaT.V.Do, sp.nov.A.Leaves; B.Innersurfaceoflimbandannulus(indicatedbyagreenarrow); C. Longitudinal section of perianth; D. Lateral view of perianth; E. Dorsal view of perianth; F. Ventral view of perianth G. Top and frontal view of perianth; H. Lateral view of gynostemium; I. Top view of gynostemium; J. Capsule. Photo credits, M. Forbes.