Lasianthus laoticus Tagane, Soulad. & Nob.Tanaka, 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 : 148-151

Lasianthus laoticus Tagane, Soulad. & Nob.Tanaka , sp. nov. Figures 3 & 4

TYPE:— LAOS. Attapeu Province: Sanamxai District , roadside, at edge of evergreen forest, 14°47′18.18″N, 106°25′24.90″E, 183 m elev., 6 July 2019, P. Souladeth, S. Tagane, N. Tanaka, K. Souttakone, Y. Suyama, K. Phengmala, N. Ishii L3024 (holotype FOF!, isotypes KAG129297 !, TNS!) .

Lasianthus laoticus is similar to L. kailarsenii Poopath, Vajrodaya & Napiroon in Napiroon et al. (2018: 208) of Thailand and L. longipedunculatus Parker (1925: 430) of Myanmar and Thailand in having conspicuous pedunculate cymes, but distinguished by appressed hairy twigs and petiole (vs. glabrous), reticulate tertiary veins (vs. parallel), and smaller triangle stipule ca. 1.8 mm long (vs. lanceolate, 3–4 mm long in L. kailarsenii and triangular, 2–5 mm long in L. longipedunculatus ). In addition to these vegetative traits, L. laoticus differs from L. kailarsenii in having cylindrical-campanulate corolla with triangular lobes 3 mm long (vs. tuber, lobes oblong-lanceolate 1.5–2 mm long), longer style 4 mm long (vs. 1.5–2 mm), and from L. longipedunculatus in having shorter peduncles 1–3 cm long (vs. 4–10 cm long), smaller linear bracts ca. 2.2 mm long (vs. leaf-like, linear-lanceolate, 8–12 mm long), and triangular calyx lobes ca. 1 mm long (vs. oblong-lanceolate, 4–4.5 mm long) ( Table 2 ).

Description:—Shrub, to 1 m high. Current year twig 2–3 mm in diam., flattened, appressed brownish hairy, glabrescent; internode 1.3–4.2 cm. Leaves opposite, petiolate; petiole 1–3 mm long, densely appressed hairy; blade ovate-oblong, 3.5–13 × 1.4–4.1 cm, subcoriaceous, adaxially dark yellow green, glossy, glabrous, abaxially gray green, densely hairy on midrib to tertiary veins, apex acuminate to aristate, tip pointed, 0.8–1.4 mm long, base cordate, margin finely undulate, midrib sunken adaxially, prominent abaxially, secondary veins 8–11 pairs, prominent abaxially, tertiary veins reticulate. Stipules triangular, ca. 1.8 mm long, brownish hairy outside, especially denser near margin and apex. Inflorescence axillary, cymose, solitary to 7-flowered; peduncle 1.3–3 cm long, pubescent, glabrescent; bract linear, ca. 2.2 mm long, pubescent. Flowers subsessile to short-stalked; pedicels up to 2.2 mm long; calyx obconical, sparsely pubescent, tube ca. 2 mm long, lobes 4, triangular, ca. 1 mm long; corolla white with a faint tinge of yellow, cylindrical-campanulate, tube 6–9 mm long, outside glabrous, inside villous in upper 1/2, lobes triangular, ca. 3 mm long, apex apiculate, outside glabrous, inside villous, stamens 4, exerted from corolla, filaments basally connate to corolla, free part ca. 1.2 mm long, glabrous, anthers ca. 2.2 mm long, ciliolate; ovary 4-locular, style ca. 4 mm long, glabrous, stigma 4-lobed, ca. 0.9 mm long. Fruits drupaceous, subglobose or ovoid, 5–6 mm long, ca. 5 mm in diam., crowned by the persistent calyx, blackish brown when ripe, sparsely appressed hairy on the surface; the persistent calyx lobes 4, linear to linear-lanceolate, ca. 1 mm long, apex acute, hirsute; pyrenes 4, grooved on the dorsal curved face, obovoid, ca. 4 mm long, 2 mm wide.

Additional specimen examined:— Champasak Province, Dong Hua Sao National Protected Area , 14°53′44.73″N, 106°01′2.36″E, 158 m elev., 13 December 2018, S. Tagane et al. L2222 [young infl.] ( FOF, KAG128322 ) .

Distribution:— Laos (so far known only from the two provinces, Attapeu and Champasak Provinces, located at the southern basin of Bolaven Plateau).

Habitat and Ecology:— The species was found in lowland evergreen forest at 150–190 m elev. Flowering and fruiting specimens were collected in July.

Etymology:— This specific epithet laoticus is derived from the country name where this species was discovered.

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

Preliminary conservation assessment:— Endangered (EN). To date, Lasianthus laoticus is known only from two populations with each ca. 30 mature individuals in the lowland evergreen forest in lower elevations at the southern basin of Bolaven Plateau, at elevation of 158 and 183 m. Considering the distance between the two localities is ca. 18 km and same environment is found in the area, the estimated extent of occupancy for this species is 900 km 2. The localities we collected the above specimens are along a recently constructed logging road, and are being gradually deforested. Therefore, we suggest the category of this species as Endangered according to the IUCN criteria B1ab(i, ii, iii) ( IUCN 2012). More accurate data on its population size and number of individuals is needed for developing a conservation plan.

Notes:— Among the species of Lasianthus in Laos, L. laoticus is easily distinguished by its slender peduncles (vs. inflorescence sessile or subsessile in the other species). It is also similar to L. lancilobus of West Kalimantan in lamina size and slender peduncles but different from L. lancilobus in having shorter petiole 1–3 mm long (vs. 6–8 mm long in L. lancilobus ), cordate leaf base (vs. acute to cuneate), 8–11 pairs of secondary veins (vs. 5–6 pairs), and small triangular calyx lobe 1 mm long (vs. lanceolate, 5 mm long) ( Table 2 ).

Figures

FIGURE 3. Isotype of Lasianthus laoticus Tagane, Soulad. & Nob.Tanaka. (Souladeth et al. L3024 (KAG129297)).

FIGURE 4. Lasianthus laoticus Tagane, Soulad. & Nob.Tanaka. A. Flowering twig; B. Portion of abaxial leaf surface; C. Inflorescence; D. Calyx; E. Fruit.All from Souladeth et al. L3024.

Tables

Table 2. Comparison of Lasianthus laoticus with three morphologically similar species. Data on L. kailarsenii, and L. longipedunculatus and L. lancilobus were retrieved from the protologue Napiroon et al. (2018), Parker (1925) and Zhu (2012), as well as their type specimens, respectively.

Characters	Lasianthus laoticus	L. kailarsenii	L. longipedunculatus	L. lancilobus
Lamina	ovate-oblong, 3.5–13 ×	lanceolate to lanceolate-	oblong, 15–20 × 4–6 cm	oblong, 6–13 × 2.5–3.5 cm
	1.4–4.1 cm	elliptic, 5–7 × 2.5–3 cm,
Petiole length	1–3 mm	1 mm	1–2 mm	6–8 mm
Hairlines on twig	appressed hairy	glabrous except base	glabrous	(sparsely) hirsute
and petiole		which is sparsely hirsute
Number of	8–11 pairs	6–8 pairs	6–8 pairs	5–6 pairs
secondary veins
Tertiary veins	reticulate	parallel	parallel	subparallel
Stipules	triangular, ca. 1.8 mm long	lanceolate, 3–4 mm long	triangular, 2–3(–5) mm	Lanceolate, ca. 3 mm long
			long
Peduncle length	1–3 cm	2.5–4 cm	4–10 cm	2.5–3 cm
Bracts	linear, ca. 2.2 mm long	lanceolate, 2–3 mm long	leaf-like, linear-lanceolate,	linear, up to 15 mm long
			8–12 mm long
Calyx lobes	triangular, ca. 1 mm long	triangular, 1–1.5 mm long	oblong-lanceolate, 4–4.5	lanceolate, 5 mm long
			mm long
Corolla lobes	triangular, ca. 3 mm long	oblong-lanceolate, with	oblong, 2 mm long	-
		lobes 1.5–2 mm long
Style length	4 mm	1.5–2 mm	-	-