Aristolochia thotteaeformis T.V.Do & Luu, 2022

Luu, Hong Truong, Nguyen, Tran Quoc Trung, Nguyen, Quoc Dat, Nguyen, Thanh Trung, Nguyen, Thanh Trung & Do, Truong Van, 2022, Aristolochia thotteaeformis, a distinct new species from southern Vietnam, Phytotaxa 547 (2), pp. 167-176 : 168-174

Aristolochia thotteaeformis T.V.Do & Luu , sp. nov. ( Figs. 1–3 )

The new species is most similar to A. philippinensis and A. humilis by sharing a cuneate to rounded leaf base, a straight perianth in pre-anthesis, then slightly curved upward, an ovoid to ellipsoid utricle, and a 5–10 mm long, cylindrical tube. However, it clearly differs from the former by having densely pubescent, zig-zag young branches with swollen nodes (vs. glabrous, straight young branches without swollen nodes), an ellipsoid to oblanceolate lamina, sparsely pubescent on abaxial surface (vs. elliptic to lanceolate, glabrous), a palmate venation (vs. pinnate), a pubescent, 6–8 mm long, lanceolate-ovate bracteole (vs. glabrous, ca. 2 mm long, narrow lanceolate), a sparsely hairy perianth (vs. glabrous), a whitish-yellow, 3.2–3.5 × 0.2–0.3 cm, narrow oblong or ensiform limb (vs. purple, 1.8–2.5 × 0.3–0.6 cm, elliptic, oblanceolate), and seeds with circular warts on the abaxial surface (vs. coarse verrucae). It is distinguishable from the latter by having zig-zag young branches with swollen nodes (vs. straight young branches without swollen nodes), an ellipsoid to oblanceolate lamina (vs. eliptic, rarely ovate), an up to 2 mm long petiole (vs. more than 2 cm long), a sparsely hairy perianth (vs. glabrous), a 3.2–3.5 × 0.2–0.3 cm, narrow oblong or ensiform limb (vs. 1.8 × 0.4–0.6 cm, oblanceolate)

Type: — VIETNAM. Ninh Thuan Province: Ninh Hai District, Nui Chua National Park , 27 May 2021, 11°42’25.52”N, 109°10’45.48”E, 89 m, H. T . Luu et al. NC305 (holotype SGN!, isotypes SGN!, VNMN!) .

Erect shrubby plant, up to ca. 1 m high. Young branches terete, zig-zag, 2.5–3 mm in diam., green, densely pubescent, with nodes swollen and internodes up to 2 cm long. Old stem terete, straight, 3–3.5 mm in diam., brown, slightly irregularly ridged to smooth. Petiole very short, ca. 2 mm long, straight, sparsely pubescent. Leaf blade ellipsoid to oblanceolate, 6–14 cm long, 3–4.5 cm wide, papery, apex acute, acuminate or cuspidate, up to 1 cm long, base cuneate to rounded, adaxially glabrous, abaxially sparsely pubescent, palmate basal nerves 1 pair, ascending close to the leaf margin and reaching upwards to ca. one-third of the length of the lamina, pinnately lateral nerves five to six pairs, venation loosely reticulate, sometime cross-venulate, faint on adaxial surface, distinct and slightly prominent on abaxial surface, margin entire, sparsely hairy. Inflorescence cymose, axillary, solitary, 2–5-flowered. Inflorescence axis 1.2–2 cm long, green, ascending, slender, rachis 2–3 mm long, pubescent. Bracteole lanceolate-ovate, clasping the axis, sessile, 6–8 mm long, 2.5–3 wide, green, base cuneate, apex acute, pubescent on both surfaces. Pedicel 2.5–3 mm long, slightly curved, green, pubescent on both surfaces. Ovary oblong-obovoid, 3.5–5 mm long, ca. 2 mm in diam., yellowish-green, shallowly 6-angled, pubescent. Perianth straight in pre-anthesis, then slightly curved upward, outside sparsely pubescent with distinctly longitudinal veins, with a distinct stipe between ovary and utricle present, 2–3 mm long. Utricle sharply delimited from the tube, ovoid or ellipsoid, 1.2–1.6 cm long, 0.6–0.8 cm diam., outside white, sparsely hairy, inside white with a broad brown band at base and sparsely glandular trichomes. Tube cylindrical, straight, 8–10 mm long, 3–3.5 mm in diam., somewhat broader at mouth, outside white, sparsely hairy, inside dark-purple or maroon, densely glandular trichomes. Limb 1-lipped, narrow-lanceolate or ensiform, 3.2–3.5 cm long, 0.2–0.3 cm wide, whitish-yellow, apex acute, glabrescent on both surfaces, veins or striations not visible. Mouth broader than tube, elliptic, 5.5–6 mm in diam., dark-brown or maroon, margins revolute, inner surface densely covered with glandular trichomes. Gynostemium 6-lobed, 4–4.5 mm high, 3.5–4 mm in diam., with a roof-like rim above the anthers and conical apices, 1.8–2 mm long. Anthers oblong, ca. 1 mm long, yellow. Capsule ovoid or rhombic, 1.2–1.5 cm long, 0.8–1 cm in diam., 6-angled, glabrescent, acropetally dehiscent. Seeds triangular or deltoid, concave-convex, 3–4 mm high, 3–4 mm wide, non-winged, densely warty on the abaxial surface, funicle broadened and covering the adaxial surface.

Etymology: —Habit and leaves of this species exhibit certain resemblance with these observed in some species of Thottea Rottb. (1783: 529) (Aristolochiaceae) . The name of new species reflects this similarity unusual among Aristolochia , especially in the Old World.

Phenology: —Flowering has been observed from May to July, and fruiting occurs from June to August.

Distribution and ecology: — Aristolochia thotteaeformis is only known from the type locality in Nui Chua National Park, Ninh Thuan Province, southern Vietnam. It grows on fertile soils at elevations of up to 500 m under a drought-deciduous woodland dominated by Strychnos nux-vomica L. (1753: 189), Pterospermum sp. , Buchanania reticulata Hance (1877: 332) , Diospyros mun A.Chev. & Lecomte (1928: 108) , Milletia sp. , Morinda cochinchinensis DC. (1830: 449) , Terminalia chebula Retz. (1789: 31) , and Spondias pinnata (L.f. 1782: 156) Kurz (1875: 42). This semi-arid low forest is located in a monsoon tropical climate with total average annual rainfall of <700 mm distributed mainly in late September to mid-December and fall within the ecoregion “Southern Vietnam Lowland Dry Forests” that is the most arid and unique ecosystem in Vietnam and possibly over Southeast Asia ( Thai 1999, Wikramanayake et al. 2002).

Conservation status: —The new species appears to have a very strict distribution that is confined to fertile soils near streams rarely found in a special semi-arid vegetation type, which has been being heavily impacted by human activities, especially illegal logging, agricultural extension, and free grazing (including cow, buffalo, sheep and goat). According to Wikramanayake et al. (2002), this forest was “the single most degraded or otherwise converted dry forest ecoregion outside of India and retains less than 10 percent of its forests, and only 2 percent are protected”. It is protected with less than 11,000 ha in Nui Chua National Park. We have surveyed this park over the last ten years and have found only two subpopulations of A. thotteaeformis : the first subpopulation with about 30 young and mature individuals distributed in an area of less than two ha and the second with six individuals scattered in an area of less than 500 m 2 which is about 3.5 km away from the first one. Given this situation, we suggest the species to be categorized as Critically Endangered (A1a or B1 and B2c, b, c or D). Urgent measures of conservation need to be implemented to ensure its long-term existence.

Taxonomic notes: —Morphologically, Aristolochia thotteaeformis is similar to some other species of the subsection Podanthemum , i.e. A. humilis , A. macgregorii , A. philippinensis , and A. sericea by sharing an erect undershrubby to shrubby habit. However, the new species is clearly distinguishable from A. macgregorii and A. sericea in having a cuneate to rounded leaf base (vs. distinctly cordate). The new species mostly resembles A. philippinensis and A. humilis by sharing a cuneate to rounded leaf base, a straight perianth in pre-anthesis, then slightly curved upward, an ovoid to ellipsoid utricle, and a 5-10 mm long, cylindrical tube, but it is clearly distinguishable from these two species by some morphological characters of young branches, leaves, petiole, inflorescence axis, bracteole, perianth, limb, and seed. A detailed morphological comparison of the new species with the most similar species is shown in Table 1 and Figure 3 .

Aristolochia thotteaeformis described here raises the number of Aristolochia species in Vietnam to 28. Furthermore, morphological characters such as the unilabiate flower, 6-lobed gynostemium, and a prominent stipe between the ovary and utricle support its placement into Aristolochia subgenus Aristolochia section Diplolobus subsection Podanthemum . As a result, there are currently four species of the subsection Podanthemum recorded for the flora of Vietnam, i.e. Aristolochia acuminata Lam. (1783: 254) , A. impressinervis C.F. Liang (1975: 15) , A. pothieri Pierre ex Lecomte (1909: 74) , and A. thotteaeformis sp.nov. ( Hwang et al. 2003, Nguyen et al. 2003, and Do 2016). In order to facilitate identification, we here provide a diagnostic key to these four species.

From a morphological point of view, Aristolochia thotteaeformis is clearly different from all the known Aristolochia species from Vietnam by having an erect shrubby habit (vs. woody lianas or twiner) and zig-zag young branches (vs. straight).

Figures

FIGURE 1. Aristolochia thotteaeformis T.V.Do & Luu sp.nov. A. Young branches; B. Cymose inflorescence in axillary and perianth straight in pre-anthesis; C. Lateral view of opened flower showing a distinct stipe (indicated by an arrow); D. Longitudinal section showing inner surface of perianth; E. Frontal view of opened flower; F. Close up of a 6-lobed gynostemium; G. Shape of capsule; H. Abaxial surface of seed showing densely circular warts. Drawn by Quyet Huu Nguyen & Truong Van Do.

FIGURE 2. Aristolochia thotteaeformis T.V.Do & Luu sp.nov. A. Erect shrub; B. Zig-zag young branches; C. Adaxial leaf surface; D. Pubescent young branches with short internodes and swollen nodes (indicated by white arrows); E. Cymose inflorescence bearing flowers with a distinct stipe (indicated by a white arrow); F. Frontal view of opened flower; G. Lateral view of opened flower; H. Longitudinal section showing inner surface of perianth; I. Close up of a 1-lipped limb and mouth; J. Close up of a 6-lobed gynostemium; K. Top view of a 6-lobed gynostemium; L. Shape of capsule; M. Abaxial surface of seed showing densely circular warts. Photographs by Hong Truong Luu, Tran Quoc Trung Nguyen, Quoc Dat Nguyen, Thanh Trung Nguyen; designed by Truong Van Do.

FIGURE 3. Morphological comparison of Aristolochia thotteaeformis T.V.Do & Luu sp.nov. (A-C) with A. philippinensis (D-F). A, D. Erect shrub and leaf shape; B, E. Cymose inflorescence on young branches and shape of internodes and nodes; C, F. Close up of lateral view of opened flowers. A-C photographed by Hong Truong Luu; D-F photographs by Scott Zona.