Lasianthus yersinii 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

75. Lasianthus yersinii V.S.Dang & Naiki , sp. nov. — Fig. 108 (plate), Fig. 104 (map)

Type: — VIETNAM. Khanh Hoa Province, Hon Ba Nature Reserve, 617 m elev., 12°06’39.77’’N, 108°58’59.23’’E, in evergreen forests, 22 November 2014, Toyama H., Tagane S., Dang V.S., Nagamasu H., Naiki A., Tran H., Yang C.J. with Cuong N.Q., Hieu H.N.P. V1964 (holotype VNM! [ VNM00042950 ]; isotypes FU!, VNM! [ VNM00042951 , VNM00042952 ], the herbarium of Iriomote Station (Japan)) .

Diagnosis: —This new species is morphologically similar to Lasianthus latifolius (Blume ex DC.) Blume ex Miq. (1857: 320) based on leaf and inflorescences shapes, but differs from the latter in having more secondary veins (7–8 on each side of midrib vs. ca. 7 on each side of midrib), bracts 1–1.5 mm long (vs. absent), larger calyx (1.5–2 mm long vs. ca. 1.5 mm long for tubes and 2.5–4 mm long vs. ca. 2.5 mm long for lobes) and fruits with 5 (vs. 6) pyrenes ( Table 3).

Description: —Shrubs, 1–3 m tall; branches and branchlets terete, 2–4 mm diam., glabrous or subglabrous to sparsely strigose on young branches, internodes 3–5 cm long. Leaves opposite, elliptic to elliptic-oblong, 15–20 × 4–6 cm, coriaceous, glabrous on both surfaces except sparsely appressed-pubescent midrib and secondary vein abaxially, apex acuminate to cuspidate, aristate 1–1.5 mm long, base acute to cuneate, margin entire; midrib conspicuous adaxially, prominent abaxially; secondary veins 7–8 on each side of midrib, ascending at an angle of 50–60° from midrib, curved to the margin, flat to slightly adaxially, distinct abaxially; tertiary veins parallel; petioles 12–15 mm long, sparsely appressed-pubescent. Stipules triangular, 2–3 mm long, appressed-pubescent. Inflorescences sessile, cymose, 1–7-flowered; bracts small, linear, 1–1.5 mm long, appressed-pubescent. Flowers sessile; calyx campanulate, 4–6 mm long, whitish pale to whitish purple, pubescent, calyx tube 1.5–2 mm long, calyx lobes 5, linear, 2.5–4 mm long; corolla not seen. Fruits drupaceous, globose, 6–7 mm long, 5–6 mm in diam., glabrous, crowned by persistent calyx lobes, orange when ripe; pyrenes 5. Seeds ovoid, 3–4 mm long, sulcate on the abaxial face, brown when dry.

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

Habitat & Ecology: —The species was growing under the shade of the evergreen forest at about 500–700 m elev., where Gnetum gnemon L. (1767: 125), Lasianthus hirsutus (Roxb.) Merr. (1952: 299) , Phyllanthus reticulatus Poir. (1804: 298) , Streblus indicus (Bureau) Corner (1962: 226) and Eustigma honbaense H. Toyama, Tagane & V.S. Dang (2016: 49) are dominant.

Phenology: —Flowering and fruiting specimens were collected in July.

Etymology: —The specific epithet refers to Dr. Alexandre Emile Jean Yersin, who first discovered the top of Hòn Bà mountain.

Vernacular name: —Xú hưƠng yersin.

Preliminary conservation assessment: — Lasianthus yersinii was collected from two populations with fewer than 200 individuals in the evergreen forest of Hon Ba Nature Reserve, where is well protected. The Extent of Occurrence (EOO) is less than 200 km 2 and the known Area of Occupancy (AOO) is less than 40 km 2. However, the natural habitat of this species is close to the road and easily affected by anthropogenic activities. Therefore, we assigned a preliminary status of this species as Vulnerable (VU) based on the IUCN (2019) guidelines.

Notes: — Lasianthus yersinii is also similar to L. calycinus Dunn (1912: 367) which is endemic to China, but differs from the latter in having longer petioles (12–15 mm vs. 8–10 mm long), bracts 1–1.5 mm long (vs. absent) and smaller calyx.

Figures

FIGURE 104. Distribution maps of Lasianthus vietnamensis, L. viridiramulis, L. vuquangensis, L. yaharae and L. yersinii.

FIGURE 108. Lasianthus yersinii V.S.Dang & Naiki (from holotype, VNM): A. Branch with fruits, B. Close-up of expanding young leaves, C. Stipules, D. Abaxial leaf surfaces, E. Inflorescence showing lateral view flower buds, F–G. Mature fruits, H. Seeds (A & F–G: photos by Shuichiro Tagane).