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Plant Focus

Quercus tonduzii with acorn
An oak found only on a volcano in Costa Rica

A New Species of Oak from Vietnam

In a paper published in PhytoKeys in August 2022, a new species of oak is described: Quercus sontraensis Ngoc, Binh & Son. The epithet derives from the location where it was found, the Son Tra Peninsula in central Vietnam. It is section a Cyclobalanopsis species closely related to two species described by Hickel and Camus in the early 1920s: Q. langbianensis and Q. cambodiensis. The authors of the paper (Nguyen Van Ngoc, Hoang Thi Binh, Hoang Thanh Son, Yoshihisa Suyama, and Tetsukazu Yahara) distinguish the new species from the other two based on morphological and phylogenetic analysis, as well as ecological differences.

Quercus sontraensis is described as a tree to 12 m tall, with lanceolate to elliptic leaves, which are covered in dense golden hair when young, later glabrescent, the margin regularly and distinctly serrate in the upper third of the leaf blade. The bowl-shaped cupule has 7–8 rings, which are all distinctly toothed, except for the two upper rings; it encloses one third of the acorn, which is broadly ellipsoid. Quercus cambodiensis, in contrast, has leaf margins that are almost entire or with a few low teeth in the upper quarter of the blade, and its cupules are cup-shaped with ring margins that are unthoothed except for the two lower rings; Q. langbianensis has cup-shaped cupules that are distinctly toothed in all rings and acorns that are obovoid to ellipsoid.

The phylogenetic analysis presented in the paper shows the new species to be distinct from Q. langbianensis and Q. cambodiensis. In addition, Q. sontraensis was collected at a relatively low elevation (340 m), while the other two species have been recorded at higher elevations, above 800 m.

Quercus constraensis
Quercus sontraensis Binh, Ngoc & Son 
A leafy twig with male inflorescences; B & C young leaves covered with dense 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).

The name Q. sontraensis was first proposed by Hoang Thi Binh in her PhD thesis at Kyushu University, dated March 2018, though strangely this is not mentioned in the paper where the name is published. The thesis, a taxonomic study of oak species in Vietnam, tentatively named 10 species found in Vietnam that had not been described, of which Q. sontraensis is the only one to have been published so far. 

Aside from Q. sontraensis, six new species of Quercus found in Vietnam have been published since 2018, all of them co-authored by Hoang Thi Binh:

Quercus baolamensis H.T. Binh & Ngoc* (2018)

Quercus bidoupensis H.T. Binh & Ngoc* (2018).

Quercus honbaensis H.T. Binh, Tagane & Yahara* (2018).

Quercus ngochoaensis H.T. Binh & T.S. Hoang (2021).

Quercus trungkhanhensis H.T. Binh & Ngoc (2018).

Quercus xuanlienensis H.T.Binh, Ngoc & T.N. Bon * (2018).

Additional photos below courtesy of Hoang Thi Binh: 

Quercus sontraensis 1
© Hoang Thanh Son
Quercus sontraensis 2
© Hoang Thanh Son
Quercus sontraensis 3
© Hoang Thanh Son
Quercus sontraensis 4
© Hoang Thanh Son
Quercus sontraensis 5
© Hoang Thanh Son
Quercus sontraensis 6
© Hoang Thanh Son
Quercus sontraensis 7
© Hoang Thanh Son
Quercus sontraensis 8
© Hoang Thanh Son
Quercus sontraensis 9
© Hoang Thanh Son

* For brief descriptions and photographs of these species, see B. Chassé and A. Coombes, “New Species from Around the World”, International Oaks 29 (2018): 30–33