Argostemma laotica Lanorsavanh & Chantaranothai, 2016

Lanorsavanh, Soulivanh & Chantaranothai, Pranom, 2016, Argostemma laotica (Rubiaceae), a new species from Laos, Phytotaxa 270 (3), pp. 223-226 : 223-226

Argostemma laotica Lanorsavanh & Chantaranothai , sp.nov. ( Figs. 1–3 )

Argostemma laotica is similar to A. concinnum Hemsley (1895 : t. 2380) in perennial herb with tuber, acute leaf apex, terminal inflorescence, 5-merous flower, triangular calyx lobes, star-shped flower and capitate stigma, but differs in having pubescent stem (vs. glabrous), leaf base oblique (vs. acute or attenuate), corolla and ovaries pubescent (vs. glabrous), and shorter pedicels of 6–7 mm long (vs. 10–20 mm long) and smaller anthers of 2.2–2.5 mm long (vs. 5–6.5 mm long), which a dehiscence by an apical pore.

Type: — LAOS. Xiangkhoang : Thathom district , Xan river , 16 Jul. 2013, Lanorsavanh 760 (holotype Biology Herbarium, National University of Laos!; isotype KKU28953 !) .

Perennial herb with tubers. Stems erect, 1–2.5 cm tall, pubescent. Stipules triangular or ovate, 1–2 × 1–1.5 mm, pubescent. Petioles 1–3 mm long, pubescent. Leaves simple, opposite (or pseudo-verticillate); blade membranous or chartaceous, elliptic, lanceolate or oblanceolate, 10–17 × 4–7 mm, base oblique, apex acute, margins entire; upper leaf surface dark green; lower leaf surface brown; both surfaces pubescent; lateral veins 3–4 pairs. Inflorescence 2- flowered, terminal; peduncles very short; bracts 2, subequal, linear or lanceolate, 3–6 × 1.5–2 mm long, green or pale green. Flowers 5-merous, actinomorphic or slightly zygomorphic; pedicels 6–7 mm long, pubescent. Calyx lobes pale green, triangular, 2–2.5 x 1.5–2 mm, erect or spreading, pubescent outside. Corolla white, star-shaped; tube 1–1.2 x 1–1.2 mm; lobes lanceolate or narrowly triangular, 5–5.2 x 1.5–2 mm, spreading, pubescent. Stamens 5; filaments free, 2.5–3.2 mm long; anthers connivent, white, basifixed, oblong, 2.2–2.5 mm long, without apical appendage, opening by an apical pore. Ovary densely pubescent; style filiform, 5–5.2 mm long, glabrous; stigma capitate, ca. 0.3 x 0.2 mm. Fruit unknown.

Distribution and ecology: —Endemic to Laos and only known from the type locality in Xiangkhoang, growing on wet rock, along river, elevation ca. 200 m.

Phenology: —Flowering in July.

Etymology: —The specific epithet refers to the country in which the specimen was collected.

Conservation status: —This species is endemic to Xiangkhoang province. Little is known about its conservation status. At present known from only one locality, it is here considered Vulnerable (VU D2) ( IUCN 2012). However, it has been overlooked, and is probably more frequent than records suggest. The landscape of Xiangkhoang province has suffered, many changes over the last 20 years due to urban development and the spread of intensive agriculture. However, many riverside sites suitable for this species still remain.

Note: —The general aspect of A. laotica is similar to A. concinnum , but differs by having indumentum on the stems, leaves, pedicels, corollas and ovaries, shorter pedicels and smaller anthers, which a dehiscence by an apical pore ( Table 1).

Figures

FIGURE 1. Distribution of Argostemma laotica in northern Laos. The closed circle (∙) indicates collection locality.

FIGURE 2. Argostemma laotica: A. habitat and habit; B. inflorescence and leaves; C. tubers, stems, leaves and inflorescences (from Lanorsavanh 760). Photos by S. Lanorsavanh.

FIGURE 3. Argostemma laotica: A. Habit; B. Leaf; C. Flower; D. Inflorescence; E. Stamens; F. Style and Stigma. Scale bars = 5 mm. Drawn by W. Thammarong.