Lithocarpus congtroiensis Ngoc & Yahara, 2021

Ngoc, Nguyen Van, Binh, Hoang Thi, Nagahama, Ai, Tagane, Shuichiro, Toyama, Hironori, Matsuo, Ayumi, Suyama, Yoshihisa & Yahara, Tetsukazu, 2021, Morphological and molecular evidence reveals three new species of Lithocarpus (Fagaceae) from Bidoup-Nui Ba National Park, Vietnam, PhytoKeys 186, pp. 73-92 : 73

Lithocarpus congtroiensis Ngoc & Yahara sp. nov.

Fig. 4

Type.

Vietnam. Lam Dong Province, Bidoup-Nui Ba National Park: Cong Troi , at edge of evergreen forest, roadside, 1752 m elev., 12°05'37.3"N, 108°22'38.8"E, 11 July 2018, S. Tagane, A. Nagahama, K. Tsuchiya, N.V. Ngoc., T.Q. Cuong V9102 [fr.] (holotype DLU!; isotypes FU!, HN!, KYO!, VNM!) .

Diagnosis.

Lithocarpus congtroiensis is most similar to L. dahuoaiensis but differs by its smaller leaf blades, more secondary veins, shorter infructescences, cupules clustered of three (vs. solitary), and bigger nut size. It is also similar to L. honbaensis but distinguished mainly by its shorter petioles, smaller leaf blade, more secondary veins, shorter infructescences, and shorter fruiting stalk (Table 2 ).

Description.

Evergreen tree, up to 25 m tall. Twigs blackish gray, glabrescent. Stipules caducous, not seen. Leaves alternate; petioles 1.1-1.8 cm long, glabrous; blades broadly elliptic, 12-18 × 4.2-7.2 cm, coriaceous, glabrous on both sides, apex acuminate, acumen 0.7-1.2 cm long, base acute to cuneate, margin entire, midrib flat or slightly prominent adaxially, strongly prominent abaxially, yellowish in vivo, brown in sicco, secondary veins 13-15 pairs, prominent abaxially, at an angle of 40-50° from the midrib, tertiary veins parallel, faintly visible abaxially. Inflorescence a terminal or axillary spike, 8-12 cm long, erect, male and female flowers separate or female below. Male flowers white, in 1-3-flowered cluster, calyx 6-lobed, lobes ovate, 0.4-0.7 mm × 0.5-0.7 mm; stamens 12, 1-1.2 mm long, anthers 0.15-0.20 mm long. Female flower always cluster of three, styles 3, stigmata pointed. Infructescences terminal, erect, 10-15 cm long, rachis grayish brown, lenticellate. Cupules clustered of three, 0.2-0.4 cm long stalked, bowl-shaped, 0.7-1.4 cm high, 2.5-3.6 m diam., enclosing 1/3-1/2 of the nut; wall woody, with tiny imbricate scales; scales triangular, obscure, covered with white-grayish indumentum. Nut broadly conical or globose, 2.1-2.6 cm high, 2.3-3.1 cm in diam., outer surface densely white tomentose; wall woody, crackled; apex shortly acuminate; basal scar slightly concave, 1.5-1.8 cm in diam.

Phenology.

Flowers were collected in December and mature fruits were collected from June to July.

Distribution.

Vietnam (so far known only from Mt. Cong Troi and Mt. Langbiang of Bidoup-Nui Ba National Park, Lam Dong Province). (Fig. 1 )

Etymology.

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

Vernacular name.

Dé đá Công TrÓi.

Additional specimens examined.

Vietnam. Lam Dong Province: Bidoup-Nui Ba National Park, Cong Troi area ; 1750 m elev., 12°04'08.5"N, 108°21'55.5"E, 18 June 2015, N. Nguyen, D. Luong, B. Hoang V3205 [fr.] (DLU!, FU!); ibid ., 1860 m elev., 12°06'06.85"N 108°23'00.32"E, S. Tagane, T. Yahara, A. Nagahama, M. Zhang, K. Tsuchiya, T. Nguyen, C.T. Nguyen V9470 [fr.] (DLU!, FU!); 1790 m elev., 12°06'03.86"N, 108°23'39.73"E, 20 Dec. 2018, T. Yahara, S. Tagane, A. Nagahama, K. Tsuchiya, C.T. Quong, P. Chhang V9555 [male and female fl.] (DLU!, FU! KAG [KAG127308]!); ibid ., 1864 m elev., 12°04'08"N, 108°21'54.5"E, 15 Jun. 2019, N.V. Ngoc, H.T. Binh, N.V. Duy, T.T. Nhung NAF200 [fr.] (DLU!); Mt. Langbiang ; 1918 m elev., 7 Oct. 2018, 12°02'48.13"N, 108°26'06.67"E, S. Tagane, T. Yahara, A. Nagahama, M. Zhang, K. Tsuchiya, T. Nguyen, C.T. Nguyen V9492 [ster.] (DLU!, FU!).

Conservation status.

Critically Endangered (CR). We found around ten individuals of L. congtroiensis along the road and inside the permanent plot at Cong Troi area, and three individuals in Mt. Langbiang, both located inside the protected area of Bidoup-Nui Ba National Park. Based on criterion D of the IUCN Red List criteria ( IUCN 2012), this species is qualified as CR. The new species is endemic to Bidoup-Nui Ba National Park, Lam Dong Province.

Figures

Figure 1. Type locality of the new species (Black dots): L 1: L. bidoupensis, L 2: L. congtroiensis, and L 3: L. hongiaoensis.

Figure 4. Lithocarpus congtroiensis Ngoc & Yahara A twig with infructescence B infructescence C, D leaves adaxially and abaxially, respectively E side view of mature cupule and nut F botton view of nut with basal scar.