Lasianthus bolavenensis Tagane & Soulad., 2023

Tagane, Shuichiro, Souladeth, Phetlasy, Tanaka, Nobuyuki, Phengmala, Kachonesak & Yahara, Tetsukazu, 2023, Two new species and a new record of Lasianthus (Rubiaceae) in Laos, Phytotaxa 585 (2), pp. 145-153 : 146-148

Lasianthus bolavenensis Tagane & Soulad. , sp. nov. Figures 1 & 2

TYPE:— LAOS. Champasak Province, Dong Hua Sao National Park [Bolaven Plateau], Paksong District, near Nong Luang Village , in lower montane forest, near a stream, 15°04′31.58″N, 106°12′30.72″E, 1226 m elev., P. Souladeth, S. Tagane, D. Kongxaysavath, S. Rueangruea, S. Suddee, Y. Suyama, E. Suzuki L3337 [fl. & fr.] (holotype FOF!, isotype KAG155702 !, TNS) .

Lasianthus bolavenensis is characterized by glabrous twigs, glabrous leaves except with sparse hairs on midrib and secondary veins abaxially when young, 4 or 5 pairs of secondary veins, and semi-orbicular bracts, by which combination it can be distinguished from the other species of Lasianthus in Laos and its surrounding countries. In Indochina, it is similar to L. bidoupensis Dang & Naiki in Dang et al. (2019: 191), an endemic species to southern Vietnam, in having almost glabrous twigs and leaves, elliptic-oblong lamina, 5-merous flowers, pinkish-white calyx, and bluish fruits, but different in having smaller leaf size (4–11.3 × 1.6–3.8 cm in L. bolavenensis vs. 16–24 × 6–8.5 cm in L. bidoupensis ), fewer secondary veins (4 or 5 vs. 6 or 7), larger anthers (2.8 mm long vs. 1–1.2 mm long), and glabrous style (vs. pubescent) ( Table 1 ).

Description:—Shrub, 1.5 m tall. Twigs glabrous, blackish when dry, terete; internode 1.7–4(–7.5) cm. Leaves opposite, petiolate; petiole 0.8–1.3 cm long, glabrous; blade ovate-elliptic, elliptic-oblong, elliptic, (4–)5.5–11.3 × (1.6–) 2.1–3.8 cm, coriaceous, glabrous except on midrib and secondary veins abaxially which is sparsely hairy, adaxially dark grayish brown, abaxially dark brownish yellow to gray-green, apex acuminate to aristate, tip pointed ca. 1.2 mm long, base cuneate, sometimes oblique, margin entire, midrib slightly concave adaxially, prominent abaxially, secondary veins 4 or 5 pairs, prominent abaxially, tertiary veins parallel. Stipule triangular, 2–2.5 mm long, apex acute, densely pubescent near margin. Inflorescence axillary, cymose, 1–4 flowered, sessile; bract semi-orbicular, 1–1.2 mm long, apex truncate, margin densely pubescent. Flowers subsessile; calyx pinkish white, ca. 6 mm long, tube ca. 4 mm long, glabrous, lobes triangular, ca. 2 mm long, apex acute, pubescent near apex; corolla pinkish white to white, cylindrical-campanulate, ca. 1 cm long, tube ca. 8.5 mm long, outside villous in upper 3/4, inside villous in upper 1/2, lobes 5, triangular, ca. 1.5 mm long, apex acute, villous. Stamens 5, inserted in corolla tube, anthers ca. 2.8 mm long, filament basally connate to corolla, free part ca. 0.2 mm long; ovary 5-locular, style 4 mm long, glabrous, stigma 4-lobed, ca. 2 mm long. Fruits subglobose or oblong, 1.1–1.2 cm long, ca. 5 mm in diam., glabrous, blue when ripe; pyrenes 5. Seeds 5, ca. 6 mm long, blackish brown when dry.

Additional specimen examined:— LAOS. Champasak Province, Dong Hua Sao National Protected Area, Seua Waterfall near Ban Nong Luang , 15°04′02.6″N, 106°12′29.9″E, 1147 m elev., 19 February 2019, P. Souladeth et al. L2501 [fl.] ( BKF, FOF!, KAG128750 !) .

Distribution:— LAOS (so far known only from the Bolaven Plateau, Champasak Province).

Habitat and Ecology:— The species was found in wet evergreen forest at elev. 1140–1280 m. Flowering specimens were collected in December and February, and fruiting in December.

Etymology:— This specific epithet bolavenensis refers to the type locality, Bolaven Plateau.

Vernacular name:— [(Xangsan Bolaven, “Xangsan” means Lasianthus in general in Lao and “Bolaven” refers to the Bolaven Plateau where the species occurs), proposed here].

Preliminary conservation assessment:— Critically Endangered (CR). From our observations by five field surveys in 2018–2020 ( Souladeth et al. 2020, Tagane et al. 2020), Lasianthus bolavenensis is locally common but narrowly restricted in a small area on Bolaven Plateau: in wet evergreen forest at elevation between 1140–1230 m, and we estimate the area of occupancy is less than 10 km 2 and mature individuals less than 1000. The most area of its habitat is located within the protected area of Dong Hua Sao National Park (formerly Dong Hua Sao National Protected Area), but some of the vicinities are being converted to coffee plantations, which might bring negative impact for the survival of this species. Given this situation, we propose Critically Endangered (CR) according to B2b(ii, iii)( IUCN 2012) for the first conservation assessment for this species.

Note:— Lasianthus bolavenensis is also similar to Lasianthus inodorus Blume (1826 –1827: 998) subsp. inodorus , widely distributed in Bangladesh, Cambodia, China, India, Indonesia (Sumatra, Java), Thailand, and Vietnam, in glabrous twigs and leaves (or sparsely puberulous on lower leaf surface) and sessile inflorescence, but different in having 4 or 5 pairs of secondary veins (vs. 6 or 7 pairs), smaller bracts 1–1.2 mm long (vs. 3–6 mm long), and blueish oblong fruits (vs. dark orange-red turning black when mature and ovoid) ( Table 1 ).

Figures

FIGURE 1. Isotype of Lasianthus bolavenensis Tagane & Soulad. (Souladeth et al. L3337 (KAG155702)).

FIGURE 2. Lasianthus bolavenensis Tagane & Soulad.A. Flowering twig; B. Abaxial leaf surface; C. Stipule; D. Flower bud and calyces; E. Calyces after anthesis; F. Flower (side view); G. Flower (front view); H. Fruits. Materials A & D from Souladeth et al. L2501; B, C, E–H from Souladeth et al. L3337.

Tables

Table 1. Comparison of Lasianthus bolavenensis with two morphologically similar species. Data on L. bidoupensis, and L. inodorus subsp. inodorus were retrieved from Dang et al. (2019) and Zhu (2012).

Characters	Lasianthus bolavenensis	L. bidoupensis	L. inodorus subsp. inodorus
Plant height	1.5 m tall	Up to 3 m tall	2–3 m tall
Lamina size	(4–)5.5–11.3 × (1.6–)2.1–3.8 cm	16–24 × 6–8.5 cm	10–20 × 2.5–6 cm
Number of secondary veins 4 or 5 pairs		6 or 7 pairs	6 or 7 pairs
Stipules	triangular, 2–2.5 mm long	triangular to broadly triangular,	triangular to ovate-lanceolate, 3–5
		5.5–6.5 mm long	mm long
Bract size	1–2 mm long	5–8 mm long	3–6 mm long
Anther length	2.8 mm long	1–1.2 mm long	-
Hairiness of style	glabrous	pubescent	-
Fruit shape and color	oblong, bluish	ovoid or ellipsoid, deep red	ovoid, dark orange-red turning
			black when mature