Lasianthus chii V.S.Dang & Naiki, 2023

Dang, Van-Son & Naiki, Akiyo, 2023, A revision of the genus Lasianthus Jack (Rubiaceae) from Vietnam, Phytotaxa 581 (1), pp. 1921-1935 : 1921-1935

12. Lasianthus chii V.S.Dang & Naiki , sp. nov. — Fig. 30 (plate), Fig. 25 (map)

Type: — VIETNAM. Khanh Hoa Province, Hon Ba Nature Reserve, 1502 m elev., 12˚06’86.09”N, 108˚58’45.07’’E, in evergreen forest, 15 June 2018, Dang V.S. & Hoang N.T.B.N., Dang 355 (holotype VNM! [ VNM00042881 ]; isotypes VNM! [ VNM00042882 , VNM00042883 ], the herbarium of Iriomote Station (Japan)) .

Diagnosis: —This new species is morphologically similar to Lasianthus chevalieri Pit. (1924: 384) based on leaf shape and fruit color, but differs from the latter in having fewer secondary veins (8–10 on each side of midrib vs. 11 on each side of midrib), shorter petioles (3–5 mm long vs. 10–15 mm long), bracts 2–3 mm long (vs. inconspicuous), smaller calyx (2–3 mm long vs. 3–6 mm long for tubes and 5–6 mm long vs. 9–14 mm long for lobes) and corolla (6–7 mm long vs. 12–13 mm long for tubes and 2–3 mm long vs. 7–8 mm long for lobes) ( Table 2).

Description: —Shrubs, up to 2 m tall; branches and branchlets terete, 1–2 mm diam., villous, internodes 2–4 cm long. Leaves opposite, elliptic, elliptic-oblong to elliptic-ovate, 8–12 × 3–5 cm, subcoriaceous, adaxially glabrous except hirsute midrib, abaxially villous, apex acuminate, aristate 1–1.5 mm long, base cuneate, margin entire; midrib conspicuous adaxially, prominent abaxially; secondary veins 8–10 on each side of midrib, ascending at an angle of 45–50° from midrib, curved to the margin, flat adaxially, distinct abaxially; tertiary veins parallel; petioles 3–5 mm long, densely villous. Stipules narrowly triangular, 2–3 mm long, and densely villous. Inflorescences sessile, cymose, 1–5-flowered; bracts linear, 1.5–2 mm long, densely villous. Flowers sessile; calyx campanulate, 7–9 mm long, purplish pale to darkish purple, densely villous, calyx tube 2–3 mm long, calyx lobes 5–6, linear, 5–6 mm long; corolla cylindrical, 8–10 mm long, white, corolla tube 6–7 mm long, pubescent outside, corolla lobes 5–6, triangular, 2–3 mm long, pubescent outside, floccose inside; stamens 5, filaments short, anthers narrowly oblong, 0.7–1 mm long; ovary with 5 locules, style linear, 7–9 mm long. Fruits drupaceous, subglobose, 10–12 mm long, 8–10 mm in diam., pilose, crowned by persistent calyx lobes, orange when ripe; pyrenes 5. Seeds ovoid, 3–4 mm long, warty to subsulcate on the abaxial face, and brown when dry.

Other specimens examined: — VIETNAM. Khanh Hoa Province, Hon Ba Nature Reserve, 1502 m elev., 12˚06’86.09”N, 108˚58’45.07’’E, in evergreen forest, 15 June 2018, Dang V.S. & Hoang N.T.B.N., Dang 351 & Dang 354 ( VNM!, the herbarium of Iriomote Station ( Japan )); in the same location, 1336 m elev., 12°07’11.42’’N, 108°57’26.46’’E, in evergreen forest, 26 November 2014, Dang V.S., Toyama H., Tagane S., Nagamasu H., Naiki A., Tran H., Yang C.J. with Cuong N.Q., Hieu H.N.P. V2286 ( KYO!, VNM!, the herbarium of Iriomote Station (Japan )) .

Distribution: — Vietnam (known from the Hon Ba Nature Reserve, Khanh Hoa Province).

Habitat & Ecology: — Lasianthus chii is only known from Hon Ba Nature Reserve , Khanh Hoa Province, southern Vietnam, where it was found in the shade of the evergreen forest at around 1200–1502 m elev .

Phenology: —Flowering from March to July, fruiting from August to November.

Etymology: —This species is named after Dr. Võ Văn Chi for his contributions to the study of medicinal plants in Vietnam.

Vernacular name: —Xú hưƠng chi.

Preliminary conservation assessment: — The new species is only known from the type locality that is within a protected area of Nature Reserve. But the habitat of this species was frequently logged and disturbed. The Extent of Occurrence ( EOO) is less than 200 km 2 and the known Area of Occupancy ( AOO) is less than 30 km 2. About 2000 individuals were observed from our field. Therefore, it should be assessed as Endangered ( EN) according to the IUCN (2019) guidelines .

Figures

FIGURE 25. Distribution maps of Lasianthus candidus subsp. candidus, L. candidus subsp. hoanglienensis, L. capitatus subsp. vietnamensis, L. chevalieri subsp. chevalieri, L. chevalieri subsp. gianglyensis and L. chii.

FIGURE 30. Lasianthus chii V.S.Dang & Naiki (from the holotype, VNM): A. Branch with flower buds and calyx, B. Close-up of young branch and leaves, C. Stipules, D. Abaxial leaf surfaces, E–G. Inflorescence showing lateral view flower buds, H. Young fruits, I. Mature fruit, J. Seeds.