Hop Hornbeam
Ostrya virginiana
Hazelnut family (Corylaceae)

Description: This medium-small tree is up to 50' tall; it has a finely branched rounded crown. The trunk is up to 2' across. On mature trees, the bark of the trunk is rough-textured and greyish brown, dividing into narrow rectangular strips; this provides the trunk with a slightly shaggy appearance. The bark of smaller branches is more smooth and gray with small lenticels. The alternate leaves are 3-5" long and 1–2" across; they are ovate, pinnately veined, and doubly serrated along their margins. Each leaf tapers rather abruptly into a slender tip. The upper leaf surface is medium green and largely devoid of hairs, while the lower surface is pale green and slightly to moderately pubescent. The slender petioles are about " long, light green, and slightly to moderately pubescent. Because Hop Hornbeam is usually monoecious, the same tree has separate male and female flowers in the form of catkins. On rare occasions, some trees are unisexual. The male catkins are 1-2" long and narrowly cylindrical in shape; they are often arranged in groups of 3 and droop downward. The female catkins occur individually at the ends of branches; they are about " long and broadly cylindrical. The blooming period occurs during mid- to late spring. Cross-pollination of the flowers is achieved by wind. Afterwards, the inflorescence of female flowers begins to swell into a drooping compound fruit about 1–2" long and –1" across; it has an appearance that is similar to the fruit of a hop vine. The nutlets of this fruit are enclosed within overlapping inflated sacs that are ovoid and somewhat flattened in shape. Initially, these sacs are greenish white and slightly shiny, but they later become dull brown. The woody root system produces no vegetative offsets; this tree reproduces by reseeding itself into new areas.

Cultivation: Hop-Hornbeam adapts to many different situations, including those with full sunlight to light shade, moist to dry conditions, and soil containing loam, clay, or rocky material. This tree is slow to develop and its wood is strong and hard.

Range & Habitat: This tree can be found in all counties of Illinois (see Distribution Map), where it is native and fairly common. Typical habitats include mesic to dry deciduous woodlands, woodland edges, limestone glades, rocky wooded slopes, edges of cliffs, edges of wooded bluffs, and abandoned fields. Hop Hornbeam is usually found in upland wooded areas. It is uncommonly cultivated as a lawn tree.

Faunal Associations: The caterpillars of several moth species feed on the foliage of Hop Hornbeam, including Acrobasis sylviella (Ironwood Tubemaker Moth) and Stilbosis ostryaeella (Ironwood Leafminer). Several other moth species are listed in the Moth Table. Other insects that feed on this tree include the leaf beetle Calligrapha ostryae, wood-boring larvae of long-horned beetles (Astylopsis macula, Hyperplatys maculata), larvae of metallic wood-boring beetles (Acmaeodera tubulus, Agrilus champlaini), Lygocoris ostryae and other plant bugs, the aphid Macrosiphum pseudocoryli, Eratoneura dira and other leafhoppers (Eratoneura spp.); see Clark et al. (2004), Yanega (1996), MacRae (1991), Knight (1941), and Dmitriev & Dietrich (2010). Several vertebrate animals rely on Hop Hornbeam as a source of food. These species include the Ruffed Grouse (buds, catkins), Downy Woodpecker (seeds), and Purple Finch (seeds). Among mammals, the Fox Squirrel, Red Squirrel, Woodland Deer Mouse, and White-Footed Mouse eat the seeds and buds, while the White-Tailed Deer browses sparingly on the twigs and leaves (Martin et al., 1951/1961; Hamilton, 1941).

Photographic Location: Crystal Lake Park in Urbana, Illinois, at the top of a wooded slope.

Comments: Another common name of this tree is Ironwood. It is easy to identify Hop Hornbeam (Ostyra virginiana) from its attractive and persistent hop-like fruits. In Illinois, its closest relative is another medium-small tree, Carpinus caroliniana (American Hornbeam). This latter tree has very smooth bark on its trunk, even when it is fully mature. The fruiting structures of American Hornbeam are distinct from the inflated sacs of Hop Hornbeam; the nutlets of American Hornbeam are subtended by 3-cleft bracts that are flat and open.