Aristolochia tadungensis T. V. Do & T. H. Luu, 2015

Do, Truong Van, Luu, Truong Hong, Wanke, Stefan & Neinhuis, Christoph, 2015, Three New Species and Three New Records of Aristolochia Subgenus Siphisia from Vietnam Including a Key to the Asian Species, Systematic Botany (Basel, Switzerland) 40 (3), pp. 671-691 : 677-678

Aristolochia tadungensis T. V. Do & T. H. Luu , sp. nov. — TYPE: VIETNAM. Dac Nong : Ta Dung Nature Reserve, 11°52′147″N, 108°01′218″E, elevation 1,246 m, 11 Jan 2011, Luu et al. TD 395 (holotype: VNMN!; isotype: SGN!).

Aristolochia tadungensis is morphologically similar to A. hainanensis and A. coadunata but it differs from them by the following characters: leaf blade coriaceous, abaxial surface densely woolly, hairs subadpressed; cymes solitary on old woody stems, axis 4–10 cm long; perianth yellowish-white; upper tube obliquely oblong funnel-shaped with purple veins, (1.8–)2–2.3(–2.4) cm high; limb nearly rectangular, 1.3– 1.5(–1.6) cm high, 1.1–1.2 cm wide; throat yellow densely covered with orange dots.

Perennial woody liana, 15–20 m high with many fasciculate and cylindrical roots. Stem slightly flattened, young branches slender, glabrescent, with a shallowly corky furrowed bark when mature, internodes 18–20 cm long. Petiole (6–) 8–10 cm long, twisted, glabrescent. Leaf blade ovate to lanceolate-ovate, (22–) 25–27 cm long, 8–10(–12) cm wide, coriaceous, base round to truncate, margin entire, apex acute or shortly acuminate, the adaxial surface dark green and glabrous, the abaxial surface densely subadpressed-woolly, basal veins three, palmate, one pair reaching half the leaf length, secondary veins four to five pairs, pinnate, middle vein and veinlets distinct, parallel or loosely reticulate, prominent abaxially, flattened adaxially. Inflorescence cymose on old woody stems, cymes solitary, each with three or four flowers, clearly separated from each other. Inflorescence axis 4–10 cm long, slightly curved, densely brown pubescent. Bracteole clasping the axis, triangular, (1.6–) 1.8– 2 mm long, 1.3–1.5 mm wide, sessile, both surfaces densely brown pubescent. Pedicel (2–)2.2–2.4 (–2.5) cm long, pendulous, densely brown pubescent. Ovary 1–1.2 cm long, 0.3– 0.4 cm in diam, densely brown villous. Perianth horseshoe-shaped, (4.0–) 4.2–4.8 cm high, outside yellowish-white with several longitudinal purple veins (variable in number, usually fewer than 5), sparsely hairy, inside white and glabrous, except for the utricle. Utricle indistinct from the tube, cylindrical, inflated, 0.6–0.7(–0.8) cm high, 1.1–1.2 cm in diam, inside with broad dark purple band and densely glandular pubescent. Lower tube horseshoe-shaped, inflated, narrower than utricle, 1.0– 1.1 cm in diam; upper tube obliquely oblong funnel-shaped, (1.8–)2–2.3(–2.4) cm high, constricted at base, 0.6–0.7 cm in diam and slightly broader at apex, (0.8–)0.9–1(–1.1) cm in diam. Limb with three unequal lobes, valvate pre-anthesis: two lateral lobes deltoid, each 1.1–1.2 cm wide, 0.5–0.6 cm high, middle lobe triangular, 0.8–0.9 cm wide, 0.4–0.5 cm high, margins of all lobes revolute during anthesis forming a trumpet-shaped limb, nearly rectangular, 1.3–1.5(–1.6) cm high, 1.1–1.2 cm wide, with two lateral lobes rib-like and narrower than the middle one (1–1.5 mm vs. 2 mm in diam, respectively), acute at apex, inner surface sparsely warty dark purple. Throat yellow, densely covered with orange dots. Annulus absent. Gynostemium with acute apices, bent inward, smooth, 5–6(–8) mm high, 3–4 mm in diam, yellow; anthers (2.2–) 2.5–3 mm long, yellow. Capsule cylindrical, 9–10(–12) cm long, (2.5–) 2.8–3 cm diam, distinctly 6-ridged, yellowish-green, densely brown villous, basipetally dehiscent. Seeds ovoid, (8–) 9–10 mm long, (4–) 5–6 cm in diam, not winged, the abaxial surface convex, the adaxial surface deeply concave with a prominent, central, longitudinal funiculus, both surfaces smooth. Figures 5 , 6 .

Vernacular Name — Common names in Vietnamese for this species are “Mô. c hýõng Tà Ðùng” and “Phòng kỷ Tà Ðùng”.

Distribution and Ecology — Known only from the core-zone of Ta Dung Nature Reserve in Dac Nong province, southern Vietnam ( Fig. 4 ). The species grows on humid soil covering granite rocks in submontane evergreen tropical forest. Dominant plants are Asteraceae , Fagaceae ( Castanopsis , Lithocarpus ), Lamiaceae , Lauraceae ( Litsea , Machilus ), Myristicaceae ( Knema , Pentaphylacaceae ( Eurya ), Rubiaceae ( Hedyotis , Psychotria ), Theaceae ( Camellia ). A tall dipterocarp tree (cf. Dipterocarpus ) is also recorded.

Phenology — Aristolochia tadungensis has been observed to flower from the middle of the dry season in southern Vietnam through December to January, but mature fruits were also recorded at the same time. Therefore, we believe that flowering may start earlier at the end of the rainy season to the beginning of the dry season through October to November.

Etymology — The specific epithet refers to the only known locality in the Dac Nong province, Ta Dung Nature Reserve.

Conservation Status — The new species is known from a single population within the core-zone of Ta Dung Nature Reserve, a large evergreen forest area. Since the locality has been severely damaged and reduced by deforestation and over-exploitation, the new species should be regarded as threatened with extinction. Following the IUCN red list criteria, a preliminary status of vulnerable (VU D2) is proposed for A. tadungensis , because of a restricted area of occupancy (typically less than 20 km 2), the number of locations (typically five or fewer) such that it is prone to the effects of human activities within a short time period in an uncertain future.

Morphological Affinities — Aristolochia tadungensis is morphologically similar to A. hainanensis , which occurs in southern China and northern Vietnam. But it is distinguishable from the latter as follows: the leaf blade coriaceous (vs. subcoriaceous), abaxial surface densely woolly (vs. villous), inflorescence axis up to 10 cm long (vs. up to 6 cm long), perianth yellowish-white, sparsely hairy with parallel purple veins (vs. yellowish, densely hairy with obscure veins), upper tube obliquely oblong funnel-shaped (1.8–)2–2.3(–2.4) cm high (vs. broadly shortened funnel-shaped, 1.1–1.3 cm high), limb nearly rectangular, 1.3–1.5(–1.6) cm high, 1.1–1.2 cm wide (vs. nearly circular, 2.2–2.5 cm wide), throat yellow, densely covered with orange dots (vs. yellow without visible dots). The new species is also similar to A. coadunata Backer , which is restricted to Sumatra and Java, Indonesia. However it is clearly distinguished from the latter by a round to truncate leaf base (vs. cordate), cymes on old woody stems, and inflorescence axis up to 10 cm long (vs. flowering in young branches and up to 2 cm long), perianth yellowish-white with parallel purple veins (vs. dark purple without visible veins), throat yellow, densely covered with orange dots (vs. without visible dots) ( Table 2).

Figures

FIG. 5. Aristolochia tadungensis. A. Abaxial leaf surface. B. Cyme on old woody stem. C. Longitudinal section of individual flower. D. Close up of gynostemium. E. Capsule. F. Adaxial view of seed. Drawings by Nguyen Huu Quyet from the type specimen.

FIG. 6. Aristolochia tadungensis. A. Adaxial leaf surface. B. Abaxial leaf surface. C & D. Inflorescence and detailed longitudinal section of the flower. E. Dorsal view of open flower. F. Front view of open flower. G. Lateral view of open flower. H. Inner surface of utricle. I. Close up of gynostemium. J. Capsule. Photographs by Luu Hong Truong from the type population.

FIG. 4. Map showing the distribution of new species and new records of Aristolochia subgenus Siphisia from Vietnam.