Lasianthus longissimus H.Zhu (2002: 397)

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

46. Lasianthus longissimus H.Zhu (2002: 397) — Fig. 72 (plate), Fig. 73 (map)

Type: — VIETNAM. Ha Giang Province, Yen Minh District , 1100–1200 m elev., 3 March 1999, Phan K.L., Pham H.H., Averyanov L. CBL2055 (holotype AAU!) .

Specimens examined: — VIETNAM. Central: Khanh Hoa Province, Hon Ba Nature Reserve, 30 km west of Nha Trang City , 1210 m elev., 21 April 2018, Dang V.S. & Hoang N.T.B.N., Dang 186 ( VNM) .

Distribution: —Endemic to Vietnam (currently known as Hon Ba Nature Reserve of Khanh Hoa Province and Yen Minh District of Ha Giang Province).

Habitat & Ecology: —Growing under the canopy of evergreen forest at around 1000–1300 m elev.

Phenology: —Flowering from March to July.

Vernacular name: —Xú hưƠng lá dài.

Notes: — Lasianthus longissimus was described as new from a Vietnamese specimen by Zhu (2002). This species is characterized by having lanceolate and apex long caudate leaves, secondary veins 5–6 on each side of midrib, calyx lobes 5, and subspathulate to obovate.

This species is similar to L. lancifolius Hook.f. (1880: 187) which was distributed in Bangladesh, Bhutan, China, India, Thailand to Vietnam, but differs in having fewer secondary veins (5–6 on each side of midrib vs. 9 on each side of midrib) and calyx lobes longer than the tube (vs. shorter). It is also similar to L. japonicus Miq. (1867: 110) in the shape of leaf blades and axillary inflorescences but distinguished by its petioles 5–7 mm long (vs. 8–10 mm long), calyx lobes 5 (vs. 4), and calyx lobes longer than the tube (vs. shorter).

Figures

FIGURE 72. Lasianthus longissimus H.Zhu (A–D from Dang 186 and A–D from CBL2055, VNM and AAU): A. Branch, B. Close-up of expanding young leaves, C. Abaxial leaf surfaces, D. Stipules, E–G. Inflorescence showing lateral view flower buds.

FIGURE 73. Distribution maps of Lasianthus longissimus, L. lucidus, L. micranthus and L. naikii.