Lithocarpus eiadthongii Sinbumr., Rueangr. & Sungkaew 2022, sp. nov.

Lithocarpus eiadthongii Sinbumr., Rueangr. & Sungkaew, sp. nov. (Figs. 1 & 2)

Diagnosis:— Lithocarpus eiadthongii is superficially similar to L. melataiensis, L. pusillus and L. vuquangensis. In terms of leaf characters, it may look like L. vuquangensis, but it is, however, much different from the latter in terms of fruit characters (having cupule size of 4−7 mm high by 8−13 mm across; cupule surface with (5)6−9 lamellae; nut size of 0.8−1.5 cm across; nut basal scar of 4−8 mm across in L. eiadthongii vs cupule size of ca 14 mm high by ca 18 mm across; cupule surface with 4−5 lamellae; nut size of 2.1−2.4 cm across; nut basal scar of ca 11 mm across in L. vuquangensis). Whilst, in terms of fruit characters, it may look similar to L. melataiensis and L. pusillus, but L. eiadthongii differs from the latter two in having a stalked cupule of 3−6 mm long (vs sessile cupule in L. melataiensis vs sessile to stalked cupule of 2−3 mm long in L. pusillus. Moreover, in terms of leaf characters, L. eiadthongii is much different from the latter two in having a leaf acumen of 3−10 cm long and leaf undersurface with sparsely white to creamy-white waxy to glabrous (vs leaf acumen of 15−22 mm long and leaf undersurface with densely yellowish brown tomentose, sometimes with simple hairs in L. melataiensis vs leaf acumen of 10−30 mm long and leaf undersurface with densely greyish brown tomentose by adpressed, minute, stellate hairs in L. pusillus) (Table 1).

Type:— THAILAND. Ranong province: Mueang Ranong district, Ngao subdistrict, Namtok Ngao National Park, hillside, UTM 47P E459665 N1090233, elev. 214 m, 4 July 2020, Sinbumroong 04072020 (holotype: BKF!; isotypes: BKF!, Kasetsart University, Faculty of Forestry, Bangkok, Thailand!, Natural History Museum, Thailand!).

Description:—Medium to large sized evergreen tree, 15−35 m tall, 20−85 cm in diam. at breast height; buttresses usually present, up to 2 m tall. Outer bark greyish brown or greenish grey, smooth and lenticellate, usually with superficial horizontal lines, becoming finely winding- and shallow-fissured to finely scaly. Inner bark easily detached from the sapwood, reddish brown to dark brown, surface of inner bark facing sapwood equipped with numerous longitudinal ridges resulting numerous longitudinal and slightly depressed purplish lines with 0.5−1.5 cm long on white to slightly creamy sapwood. Branchlets yellowish green in vivo and reddish brown to dark brown in sicco, grooved, sparsely covered with white wax and lenticels, becoming glabrous. Terminal buds tiny, ovoid, ca. 1 by 1 mm; scaly, scales ovate, spirally imbricate. Stipules not seen. Leaves simple, spirally arranged along twig, not crowded near the end of each flush; blades narrowly elliptic, lanceolate-elliptic, oblong-ovate to lanceolate-ovate, (linear-elliptic in sapling stage,) thin coriaceous, rigid, 6−12.5 by 1.5−3.5 cm; adaxially green, glabrous, dull to glossy, abaxially pale greyish to creamy green, sparsely covered with white to creamy-white wax to glabrous; base acute or cuneate to slightly attenuate, apex acute to bluntly acuminate, acumen 3−10 mm long; margin entire, sometimes slightly undulate; midrib thin, slightly raised on both surfaces; secondary veins (9−)11−13(14) pairs, thin, obscure to slightly distinct both sides, subparallel, at an angle of 50°−60°, slightly arcuating and faintly anastomosing near the margin; veinlets fine reticulated, irregular or areolate, obscure on both sides; petiole 6−10 mm long, 1.3−2 mm in diam., usually straight to slightly curved, adaxially furrowed, abaxially rounded, sparsely covered with white to creamy-white wax to glabrous. Inflorescences usually androgynous (terminal) and branched, occasionally female (subterminal) and unbranched, erect, 4−10 cm long, peduncle 1−2 mm in diam. (androgynous inflorescence) or 1.5−3 mm (female inflorescence), densely covered by creamy stellate and single hairs; bracts and bracteoles deltoid to ovate-acute, ca 0.1−0.4 mm. Male flowers solitary on the upper part of androgynous inflorescence; perianth 5−6-lobed, coriaceous, broadly ovate-acute to broadly ovate-rounded, 0.3−0.5 by 0.5−1.2 mm; stamens 10−12; filaments 0.8−1.1 mm long, anthers 0.2−0.3 mm long; pistillode globose, 0.5−0.8 mm in diam. Female flowers solitary on the lower part of androgynous inflorescence or in clusters of 2−7 on female inflorescence; perianth 5−6-lobed, coriaceous, broadly ovate-acute to broadly ovaterounded, 0.3−0.6 by 0.3−0.7 mm; staminodes 10−12, rudimentary; styles 3(4), conical, 0.2−0.4 mm long, erect to slightly recurved. Infructescence woody, as long as inflorescence. Ripe cupule solitary (that from female inflorescence not seen); 3−6 mm stalked, lamellate, usually set in 2−3 regular lines; deeply cup or obconical, 4−7 mm high, 8−13 mm across; densely and creamy tomentose with stellate and simple hairs, lamellate; wall woody, thin; rim thin, enclosing 1/6−1/5 part of the nut; lamellae distinct, rim entire or faintly denticulate, set in (5)6−9 regular lines. Nut obovoid or ovoid, 1.5−2.2 cm long by 0.8−1.5 cm across, greater part glabrous, only densely covered with appressed creamy stellate and single hairs upward, chocolate-brown, base slightly rotundate to rotundate-truncate, top sharply acute; scar concave, 4−8 mm in diam., 0.7−1.4 mm deep; wall bony, thin, 0.5−1 mm thick.

Etymology:—The specific epithet eiadthongii is named in honour of a well-known Thai dendrologist, Associate Professor Wichan Eiadthong who specialized in many families of Thai flora including Fagaceae (Eiadthong, 1993).

Vernacular:—Ko look eiad (Thai), meaning an oak tree with small fruit.

Ecology and distribution:— Currently, it is only known from peninsular Thailand; in Namtok Ngao National Park and Klong Naka Wildlife Sanctuary of Ranong province and Si Phang-nga National Park of Phangnga province. They grow in the co-dominant and intermediate layers of the evergreen forest canopy, particularly along the hillsides, between 60 m and 260 m elevation.

Conservation status:— Lithocarpus eiadthongii is, so far, known from only three populations, all of them occur in three neighboring protected areas. According to the IUCN Red List categories and criteria (IUCN Standards and Petitions Committee, 2019), this plant could be assigned to a category of Vulnerable (VU) D2 based on its limited area of occupancy and the low number or known populations. However, insufficient data exists regarding its distribution, so we provisionally propose the species conservation status as Data Deficient (DD).

Additional specimens examined:— Thailand. Ranong province, Suk Samran district, Naka subdistrict, Klong Naka Wildlife Sanctuary, hillside, UTM 47P E445772 N1045984, elev. 63 m, 12 May 2021, Sinbumroong 12052021- 3 (BKF!, KUFF!, THNHM!); Phangnga province, Khura Buri district, Bang Wan subdistrict, Si Phang-nga National Park, evergreen forest, 47P E438646 N992049, elev. 253 m, 3 June 2021, Sinbumroong 03062021 (BKF!, KUFF!, THNHM!).