Ostrya is a genus of eight to 10 small deciduous trees belonging to the birch family Betulaceae. Its common name is hophornbeam in American English and hop-hornbeam in British English. It may also be called ironwood, a name shared with a number of other plants.
The genus is native in southern Europe, southwest and eastern Asia, and North and Central America. They have a conical or irregular crown and a scaly, rough bark. They have alternate and double-toothed birch-like leaves 3–10 cm long. The flowers are produced in spring, with male catkins 5–10 cm long and female catkins 2–5 cm long. The fruit form in pendulous clusters 3–8 cm long with 6–20 seeds; each seed is a small nut 2–4 mm long, fully enclosed in a bladder-like involucre.
The wood is very hard and heavy; the name Ostrya is derived from the Greek word ostrua, "bone-like", referring to the very hard wood. Regarded as a weed tree by some foresters, this hard and stable wood was historically used to fashion plane soles.
- Ostrya carpinifolia Scop. - European hop-hornbeam - Mediterranean region of southern Europe, Middle-east, Turkey, Lebanon, Caucasus
- Ostrya chisosensis Correll - Chisos hophornbeam, Big Bend hophornbeam - endemic to Big Bend National Park in Texas
- Ostrya japonica Sarg. - Japanese hophornbeam - Japan, Korea, northern China
- Ostrya knowltonii Coville - Knowlton hophornbeam, western hophornbeam, wolf hophornbeam - Utah, Arizona, New Mexico, Texas
- Ostrya multinervis Rehd. - Central Chinese hop-hornbeam - central China
- Ostrya rehderiana Chun - Zhejiang hop-hornbeam - Zhejiang Province in China
- Ostrya trichocarpa D.Fang & Y.S.Wang - GuangxiProvince in China
- Ostrya virginiana (Mill.) K. Koch - eastern hophornbeam, American hophornbeam, Ironwood - eastern US, eastern Canada, Mexico, Guatemala, El Salvador, Honduras
- Ostrya yunnanensis W.K.Hu - Yunnan hop-hornbeam - Yunnan Province in China
- †Ostrya oregoniana (fossil)
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