Quercus sontraensis Ngoc, H.T.Binh & Son, 2022

Ngoc, Nguyen Van, Binh, Hoang Thi, Son, Hoang Thanh, Suyama, Yoshihisa & Yahara, Tetsukazu, 2022, A new species of Quercus genus (Fagaceae) from Son Tra Peninsula, Central Vietnam, PhytoKeys 206, pp. 61-73 : 61

Quercus sontraensis Ngoc, H.T.Binh & Son sp. nov.

Fig. 4

Diagnosis.

Quercus sontraensis is morphologically similar to Q. cambodiensis and Q. langbianensis in leaf shape (lanceolate to elliptic), cupules with 6-9 rings and cupule enclosing less than ½ of the nut. However, Q. sontraensis is distinguished from Q. cambodiensis by its leaf margin regularly and distinctly serrate on the upper 1/3-1/4 (-1/5) of the lamina (vs. almost entire or with a few low teeth in upper 1/4), bowl-shaped cupule (vs. cup-shaped), cupule bract margin distinctly toothed in all rings, except two upper rings (vs. entire, except distinctly toothed in two lower rings) and differs from Q. langbianensis in having bowl-shaped cupule (vs. cup-shaped), cupule bract margin distinctly toothed in all rings, except two upper rings (vs. distinctly toothed in all rings), broadly ellipsoid nut (vs. obovoid to ellipsoid) and slightly convex nut scar (vs. convex).

Type.

Vietnam. Da Nang City, Son Tra Peninsula, Son Tra Nature Reserve , in evergreen forest, alt. 340 m, 16°08'22.90"N, 108°15'28.85"E, 9 October 2016, Son H.T., Binh H.T., Ngoc N.V. QC201 (holotype DLU!, isotypes HN!, VNM!, VAFS!) .

Description.

Tree, 12 m tall. Terminal and lateral buds ovoid, 3-5 mm long, 1.5-3 mm in diam., scales in 3-5 rows, imbricate, ovate-triangular, ca. 1.5 × 2 mm, apex obtuse, margin yellowish-brown ciliate, appressed hairy on both surfaces. Young twigs greyish-brown, 1.5-2 mm in diam., densely curly golden hairy, sometimes sulcate, old twigs greyish-brown, glabrous, lenticellate. Leaves alternate; blades elliptic to elliptic-lanceolate, 7-12.5 × 2.2-3.5 cm, acuminate or sometimes acute at apex, cuneate at base, margin regularly and distinctly serrate in the upper 1/3-1/4 (-1/5), densely golden hair on both surfaces when young, glabrescent, midrib sunken adaxially, prominent abaxially, lateral veins (8-)11-14 pairs, straight and running into the teeth of margin, slightly sunken adaxially, prominent abaxially, at an angle of 45-50(-52) degrees from midrib, tertiary veins scalariform, faint on the upper surfaces and conspicuous on the lower surfaces; petioles (0.7-)1-1.5 cm long, densely curly golden hairy when young, soon glabrous. Male inflorescence 7-9 cm long. Female inflorescence 2.5-3.5 cm long, female flowers solitary. Infructescences axillary or terminal, erect, rachis 0.5-0.8 (-1.2) cm long, 3-4 (-6) mm in diam., densely golden hairy. Fruits 1-3, 3-3.3 cm long (including cupule), sessile; cupules bowl-shaped, 1.2-1.7 (-1.9) cm long, 1.3-2.2 cm in diam., enclosing 1/3 of the nut when mature, both outside and inside covered with densely appressed yellowish-brown hairs, wall ca. 1.5-3 mm thick, comprising scales, scales arranged in 7-8 rings, margin of the ring distinctly toothed in all rings, except two upper rings; nut broadly ellipsoid 2.3-2.6 cm long, 1.7-2.0 cm in diam., densely golden hairy, apex nearly flat, densely appressed curly golden hairs around stylopodia, stylopodia up to 1.5 mm long, basal scar 1.1-1.3 cm in diam., slightly convex, glabrous.

Distribution.

Vietnam. Da Nang City, Son Tra Nature Reserve.

Etymology.

The specific epithet is derived from the district name of the type locality, Son Tra Nature Reserve, Son Tra Peninsula, Da Nang City, Central Vietnam.

Vernacular name.

Sồi Sơn Trà (suggested here).

Phenology.

Flowering from January to March, fruiting specimens were collected from September to October.

Additional specimens examined.

Vietnam. Da Nang City, Son Tra Peninsula, Son Tra Nature Reserve , in evergreen forest, 385 m elev., 16°07'41.7"N, 108°15'55.7"E, 20 September 2019, Son H.T. QC202 [fr.] (DLU!, VAFS!); ibid., 428 m elev., 16°07'00.3"N, 108°17'40.5"E, 20 September 2019, Son H.T. QC203 [fl.] (DLU!, VAFS!) .

Preliminary conservation status.

During our floristic survey inside the protected area of Son Tra Nature Reserve, less than 10 mature individuals of Quercus sontraensis were found in the evergreen forest, from 340 to 430 m altitude. According to the criteria established by the IUCN Red List ( IUCN 2019), Q. sontraensis is qualified as Critically Endangered (CR), based on the extent of occurrence (EOO 1.47 km2) and area of occupancy (AOO 12.0 km2) [CR B1ab(i,ii,iii) 1 B2ab(i,ii,iii)].

Figures

Figure 4. Quercus sontraensis Binh, Ngoc & Son A leafy twig with male inflorescences B, C young leaves covered with densely golden hairs D mature fruits E stylopodium F, G side and base of the cupule H inside of the cupule I nut (lateral view) K nut (top view). Materials from Son et al. QC 201.