Vietnam. Lam Dong Province: Bidoup-Nui Ba National Park, in hill evergreen forest dominated by the species of Fagaceae, 1698 m elev., 12°09'52.95"N, 108°32'00.38"E, 24 February 2016, S. Tagane, H. Toyama, H. Nagamasu, A. Naiki, V.S. Dang, N.V. Ngoc, J. Wai V4320 [fr.] (holotype DLU!, isotypes FU!, HN!, KYO!, VNM!).

Lithocarpusbidoupensis is most similar to L.blaoensis but differs in its shorter leaf blades, petioles and infructescences, and bigger cupules and nuts. The new species is also similar to L.licentii but distinguished from L.licentii by its shorter petioles, fewer secondary veins (10–12 pairs in L.bidoupensis vs. 12–15 pairs in L.licentii), much shorter infructescences, clustered cupules (vs. solitary), cupule covering less than 1/3 of the nut (vs. 1/2–2/3 of the nut), and concave basal scar of the nut (vs. convex) (Table 2).

Evergreen tree, up to 27 m tall. Branches yellowish green when young, turning greyish brown when old, glabrous, sparsely lenticellate. Terminal and lateral buds ovoid, up to 7 mm long. Leaves alternate; petiole 0.3–0.4 cm long, glabrous; blade elliptic to oblong-elliptic, obovate-elliptic, 6–11.6 × 2.8–5.3 cm, coriaceous, glabrous, glossy green on both surfaces, apex acuminate or attenuate, acumen up to 0.9 cm long, base cuneate, rarely obtuse, margin completely entire, midrib prominent on both surfaces, secondary veins 10–12 pairs, prominent abaxially, at an angle of 55–70° from the midrib, tertiary veins scalariform-reticulate, visible abaxially. Inflorescences not seen. Infructescences a woody spike, 8.4–11.5 cm long. Cupules sessile, usually in cluster of 3, fused at the base each other, depressed obconical or saucer-shaped, 0.71–1.40 cm high, 2.13–2.80 cm in diam., enclosing 1/4–1/3 of the nut, pubescent with short grayish indumentum outside; wall woody, ca. 2 mm thick, with brown triangular scales outside, the scales up to 4 × 4 mm, imbricate, arranged in 3 or 4 interrupted concentric rings. Nut broadly ovoid-conical to depressed ovoid-globose, 1.5–1.6 cm high, 2.1–2.3 cm in diam., glabrous, brown to blackish brown; basal scar slightly concave, 1.4–1.9 cm in diam.

Unknown. Fallen fruits were collected in February.

Vietnam (Khanh Hoa and Lam Dong provinces) (Fig. 1).

The specific epithet is derived from the type locality, Bidoup-Nui Ba National Park, Lam Dong Province, Vietnam.

Dé đá Bidoup

Vietnam. Lam Dong Province: Bidoup-Nui Ba National Park; 1602 m elev., 12°09'27.6"N, 108°32'06.6"E, 24 Mar. 2018, T. Yahara, H. Nagamasu, H. Toyama, M. Zhang, A. Nagahama, N.V. Ngoc, K. Tsuchiya V7850 [ster.] (DLU!, FU!); ibid., 1656 m elev., 12°09'36.61"N, 108°32'11.16"E, 24 Mar. 2018, T. Yahara, S. Tagane, M. Zhang, A. Nagahama, K. Tsuchiya, N.V. Ngoc, H.T. Binh, T.Q. Cuong V8190, V8417 [ster.] (DLU!, FU!); ibid., 1669 m elev., 12°09'36.65"N, 108°32'11.18"E, 29 Apr. 2019, N.V. Ngoc, H.T. Binh, N.V. Duy, T.T. Nhung NAF122 [ster.] (DLU!); ibid., 1669 m elev., 12°09'36.62"N, 108°32'11.25"E, 29 Apr. 2019, N.V. Ngoc, H.T. Binh, N.V. Duy, T.T. Nhung NAF185 [ster.] (DLU!). Khanh Hoa Province: Son Thai Commune, Khanh Vinh District, in evergreen; 1430 m elev., 12°10'42.09"N, 108°43'32.59"E, 23 Apr. 2019, T. Yahara, S. Tagane, A. Nagahama, N. Komada, V.N. Ngoc, H.V. Thanh V9940 [ster.] (DLU!, FU!).

Critically Endangered (CR). From our intensive field survey in Bidoup-Nui Ba Naitonal Park and its vicinities from 2015 to present (Tagane et al. 2017 & 2020, Binh et al 2018b), Lithocarpusbidoupensis was found only in a narrow area within the protected areas of Bidoup-Nui Ba National Park, and its adjascent area of Son Thai Commune at the elevation range between 1400 and 1669 m. In the area, we observed fewer than 50 mature individuals. Based on criterion D of the IUCN Red List criteria (IUCN 2012), this species is qualified as CR.