Lasianthus vuquangensis V.S.Dang, Naiki & Yahara (2021:26)

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

73. Lasianthus vuquangensis V.S.Dang, Naiki & Yahara (2021:26) — Fig. 106 (plate), Fig. 104 (map) Type: — VIETNAM. Ha Tinh Province, Vu Quang National Park , 1130 m elev., 26 July 2015, Yahara T., Toyama H., Tagane S., Nguyen N.,

Yang C.J., Nguyen H. V3806 ( holotype VNM! [ VNM00042946 ]; isotypes DLU!, FU!, the herbarium of Iriomote Station ( Japan)) .

Specimens examined: — VIETNAM. Central: Ha Tinh Province, Vu Quang National Park, 1130 m elev., 18˚15’34.07”N, 105˚20’47.01’’E, in lower montane forest, 26 July 2015, Yahara T., Toyama H., Tagane S., Nguyen N., Yang C.J., Nguyen H. V3806 (holotype VNM!; isotype DLU!, FU!, the herbarium of Iriomote Station (Japan)); in the same location, 1240 m elev., 18˚12’31.06”N, 105˚23’42.05’’E, in lower montane forest, 21 June 2016, Yahara T., Nguyen N., Toyama H., Tagane S., Okabe N., Nguyen H. V 5632 ( DLU, FU, the herbarium of Iriomote Station (Japan )) .

Distribution: —Endemic to Vietnam (known only from the Vu Quang National Park, Ha Tinh Province).

Habitat & Ecology: —Evergreen forest, in shaded places at 1000–1240 m elev.

Phenology: —Flowering and fruiting from April to July.

Vernacular name: —Xú hưƠng vũ quang.

Notes: — Lasianthus vuquangensis is similar to L. rhinocerotis Blume (1826: 996) in the branches and branchlets densely brown-villous, the shape of leaves and calyx lobes 6, but differs from the latter in having smaller leaves (7–10 × 1.5–2.5 cm vs. 9–18 × 3–6.5 cm), fewer secondary veins (5–6 on each side of midrib vs. 9–12 on each side of midrib), bracts 1–2 mm long (vs. 6–15 mm long), smaller calyx lobes (1–2 mm long vs. 3 mm long), larger corolla tubes (6–8 mm long vs. 4 mm long) and fruits with 6 (vs. 5) pyrenes.

It is also similar to L. rhinocerotis subsp. pedunculatus (Pit.) H.Zhu (1998: 154) which is distributed in China and Vietnam, but differs from the latter in having smaller leaves (7–10 × 1.5–2.5 cm vs. 15–21 × 4–7 cm), fewer secondary veins (5–6 on each side of midrib vs. 9 on each side of midrib), bracts 1–2 mm long (vs. 6–12 mm long), smaller calyx lobes (1–2 mm long vs. 3 mm long), larger corolla tubes (6–8 mm long vs. 4 mm long) and fruits with 6 (vs. 4–5) pyrenes.

Figures

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

FIGURE 106. Lasianthus vuquangensis V.S.Dang, Naiki & Yahara (from V3806, VNM): A. Branch with flower buds; B. Close-up of expanding young leaves; C. Stipules; D. Abaxial leaf surfaces; E–G. Inflorescence showing side view calyx and flower; H–I. Fruits; J. Seeds (A, D, F–H: photos by Shuichiro Tagane).