Species Spotlight: Quercus tarokoensis Hayata

Quercus tarokoensis (local name 太鲁阁栎 tai lu ge li, "oak of Taroko") is a fairly unknown oak species, restricted to eastern Taiwan. It occurs throughout low to mid elevation on steep slopes (400-1,300 m) and is often reported on calcareous substrates, such as limestone complexes. According to the first description by Hayata (1918), the species is somewhat similar to Q. spinosa but can be distinguished by the “more acute, smaller, thinner and less wrinkled leaves.” The species epithet refers to Taroko Gorge in Taroko National Park, where the specimen described by Hayata was found. The name ultimately derives from a word in the Truku language (spoken in northern Taiwan) which means magnificent or beautiful, applied in reference to the landscape. 

Up to 18 species of oaks have been reported from Taiwan, in addition to 25 species in other Fagaceae genera (Fagus: 1; Lithocarpus: 15; Castanopsis: 9). Of the oaks, 7 are endemic to Taiwan¹: Quercus hypophaea, Q. liaoi, Q. longinux, Q. morii, Q. stenophylloides, (all section Cyclobalanopsis), Q. tarokoensis, and Q. tatakaensis (both section Ilex).

The topography in Taiwan is extreme—the west has flat to gently rolling plains while the eastern part is dominated by mostly rugged forest-covered mountains running northeast-southwest, with over 200 peaks above 3,000 m. Over 55% of the island remains forested, with most of it contained within the eastern mountain ranges. A full overview of all species on the island is being prepared in advance of the IOS Conference to be held in Taiwan in 2021 and can be found on the Asian Fagaceae webportal. 

Q. tarokoensis can occur as a shrub, but can also grow as trees up to 12 m tall. Petioles are short (3–5 mm), usually brownish, tomentose. Leaves are narrowly oval, leathery, 2–4 cm long and 1.5–2.8 cm wide. Midrib above occasionally reported with or without brown stellate hairs. Basal section of the midrib below sometimes with stellate hairs. Leaf apex acuminate, base (sub-)cordate. Margin with spiniform teeth, apically with 1–2 (3–5) pairs of teeth. Midvein and secondary veins (5–10 pairs), adaxially inconspicuous. 

Branchlets are generally slender, grayish to grayish-brown pubescent, glabrescent and lenticellate, becoming glabrous at later stages. Lenticels are brownish and orbicular. Bark reddish to grey-brown. Cupule cup-shaped, 5–7 mm wide × 1–1.3 cm deep, enclosing up to ¼–½ of the nut. Bracts covering the cup appressed, ovate, ca. 1 mm long, densely grayish brown pubescent except for apex. Nut ovoid to narrowly ovoid, 1.4–1.8 cm long and 0.8–1 cm across. Nut glabrous, carrying a scar ca. 3 mm in diameter. Flowering commonly occurs in June–July, resulting in fruiting throughout November–December of the following year. 

Preliminary phylogenetic analyses using molecular data (Yang et al. 2018) have suggested a close relationship of Quercus tarokoensis with Q. variabilis, Q. dolicholepis, and Q. baronii. 

All photos taken in Taiwan by Ming-I Weng © and shared on www.asianfagaceae.com (2020)

Further Reading

Hélardot, J-L. “Quercus tarokoensis.” Oaks of the World. http://oaks.of.the.world.free.fr/quercus_tarokoensis.htm  [accessed January 22, 2020]

Hayata, B. (1911–1921). “Quercus tarokoensis” - in: Icones plantarum formosanarum nec non et contributiones ad floram formosanam. Vol. 7, pp. 38–39, and Plate XI. Taihoku: Bureau of Productive Industry, Government of Formosa. Taiwan. Shokusankyoku.

Strijk, J.S. “Quercus tarokoensis Hayata” www.asianfagaceae.com.  https://www.asianfagaceae.com/quercus/quercus_tarokoensis/  [accessed January 22, 2020]

Trehane, P. (2007 onwards). “Quercus tarokoensis.” The Oak Names Checklist. http://www.oaknames.org/search/fullname.asp?id=684  [accessed January 22, 2020]

Yang, Y., Zhou, T., Zhu, J., Zhao, J. and Zhao, G., 2018. Characterization of the complete plastid genome of Quercus tarokoensis. Conservation Genetics Resources 10(2), pp.191–193.