Lithocarpus dahuoaiensis (Fagaceae), a new species from Lam Dong Province, Vietnam

Abstract Lithocarpus dahuoaiensis Ngoc & L. V. Dung, a new species from the Central highland of Vietnam, is described and illustrated. The new species is morphologically similar to Lithocarpus macphailii (M. R. Hend.) Barnett or Lithocarpus encleisocarpus (Korth.) A. Camus in having completely entire leaf margin, solitary cupule, long stalks of fruits, deeply cup-shaped or turbinate cupules, with a number of horizontal filiform lines. The species differs in its nut enclosure ca. 1/2 – 2/3 of the nut, adaxially glabrous leaf blades, secondary veins 11–12 pairs and faintly to very faintly visible hairs on the outside of the cupule. A table showing the morphological comparison of Lithocarpus dahuoaiensis with Lithocarpus macphailii and Lithocarpus encleisocarpus is also provided.


Introduction
Lithocarpus Blume is the second largest genus of the family Fagaceae, comprising 341 species (Th e Plant List 2013). Th e genus is commonly known as Stone Oaks and widely distributed throughout the tropical and sub-tropical broad-leaved evergreen forests in East and Southeast Asia, extending to New Guinea (Cannon 2001, Phengklai 2008. In North America, one species of Lithocarpus, L. densifl orus (Hook. & Arn.) had been known, but has recently been treated as a member of a new monotypic genus Notholithocarpus (Manos et al. 2008). Th e center of diversity is in East to Southeast Asia, where 123 species are enumerated in China (Huang et al. 1999), 58 species in Th ailand (Phengklai 2008, Strijk et al. 2014) and 115 species in Vietnam (Ho 2003, Ban 2005.
In Vietnam, the species of Fagaceae are highly diversifi ed and can be seen in various forest types, from dry evergreen forest at lowland to montane evergreen forest at high mountains. A total of 216 species and two varieties in six genera have been recorded in the country (Ho 1999, Ban 2005, Linh et al. 2013, Vuong and Xia 2014, which represents 66% of the total world genera and 24% of the total world species diversity in this family. One species of Fagus L., two species of Castanea Mill., 54 species of Castanopsis (D. Don) Spach., 43 species of Quercus L., one species of Trigonobalanus Forman and 115 species with two varieties of Lithocarpus have been found, indicating that Lithocarpus is the largest and most diversifi ed genus of the family in Vietnam. Recently, several taxonomic works on Fagaceae of Vietnam were published (Deng et al. 2010, Linh et al. 2013, Vuong and Xia 2014, indicating that taxonomic studies of the family Fagaceae in Vietnam are still required. Lam Dong Province is located in Central highland of Vietnam ( Fig. 1) and has long been known as one of the biodiversity hotspots in Vietnam. In June 2015, the International coordinating Council of UNESCO's Man and the Biosphere Program added 20 new sites to the World Network of Biosphere Reserves, among which Langbiang biosphere reserve in Lam Dong Province was one of the sites selected (UNESCO 2015). In the region, 3,490 species of vascular plants have been recorded, including 131 and 45 threatened species which are listed in Vietnam's Red Book and IUCN Red List Categories, respectively (Ban et al. 2007, IUCN 2012. As for Fagaceae, 90 species, including 30 species of Lithocarpus, are recorded from Lam Dong Province (Ho 2003, Ban 2005, Dung 2005).
During our fl oristic inventory in Lam Dong Province in 2015, we discovered several individuals resembling species of the genus Lithocarpus. Further study revealed that these did not resemble any species described previously. Here, these are described and illustrated as Lithocarpus dahuoaiensis Ngoc & L. V. Dung, sp. nov.

Material and methods
Th e new species was discovered through literature review, as well as a thorough examination of specimens in the herbaria at ANDA, BKF, DLU, FU, HN, K, KYO, L, P, VNM and digital images of specimens on JSTOR Global Plants (https://plants.jstor. org/), Herbier National de Paris, Muséum National d'Histoire Naturelle (P).  distinct by its cupules enclosing ca. 1/2-2/3 of the nuts (vs. cupules almost completely covering the nut in L. macphailii and L. encleisocarpus), surface of the cupule densely tomentose inside and subtle hairy to very subtle hairy outside (vs. outside densely fulvous tomentose in L. macphailii and outside densely fulvous tomentose by stellate hairs in L. encleisocarpus), leaf blades glabrous adaxially, undersides covered with very short soft hairs and subtle (vs. densely glaucous tomentose with adpressed, stellate hairs abaxially in L. macphailii, pubescent then glabrescent abaxially in L. encleisocarpus), secondary veins 11-12 pairs (vs. 12-16 pairs in L. macphailii and 8-10 pairs in L. encleisocarpus).
Phenology. Mature fruits were collected in June. Distribution and habitat. Vietnam (so far known from Lam Dong Province and Dong Nai Province split by a boundary along National highway 20). (Figure 1) Etymology. Th e specifi c epithet is derived from the type locality, Da Huoai, Lam Dong Province, Central Highland Vietnam.
Conservation status. Data Defi cient (DD). Th ree fruiting individuals were found at the type locality, along the Chuoi pass of the 20 National highway. In addition, a   staff member of Dong Nai Culture and Nature Reserve has collected this species at Ma Da, Vinh Cuu, Dong Nai Province, indicating its wide distribution around the type locality. However, at present we have no reliable information on its population size. Further investigations are needed to determine the conservation status and actual population size in its natural habitat.