Ostrya virginiana (Ironwood)

Plant Info
Also known as: American Hop-hornbeam, Eastern Hop-hornbeam
Genus:Ostrya
Family:Betulaceae (Birch)
Life cycle:perennial woody
Origin:native
Habitat:part shade, shade, sun; average to dry soil; hardwood forest, upland slopes, wooded bluffs, old fields
Bloom season:April - May
Plant height:20 to 50 feet
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: raceme Cluster type: spike

[photo of winter male catkins] Male and female flowers are borne separately on the same tree (monoecious) in dangling clusters called catkins. Male catkins are in groups of 1 to 4 from the tips of 1-year-old branchlets, ¾ to 2¼ inch long, developing in fall, the flowers an appressed, reddish-brown scale-like bract that turns greenish and expands out in spring.

[photo of female catkin] Female catkins are 1/8 to ½ inch long at the tips of first year branchlets, the flowers with a spreading, green bract and thread-like red styles.

Leaves and bark: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are simple and alternate, soft to the touch, the blade oval-elliptic, 2 to 5 inches long, 1 to 2 inches wide, tapered to a pointed tip, the base rounded and symmetrical, sharply double-toothed along the edges. The upper surface is dark green with fine, velvety hairs, lower surface lighter green, hairy, especially along the veins, with tufts of hairs in vein axils. Leaf stalks are hairy, often glandular hairy.

[photo of twig] Twigs are brown to reddish with downy hairs and scattered white lenticils (pores), are often glandular hairy, and become smooth the second year.

[photo of mature trunk] Older bark is grayish brown, thin and finely textured with vertical, rectangular plates. Trunks can reach 14 inches diameter.

Fruit: Fruit type: capsule/pod

[photo of mature fruit] The fruit is a small, oval nutlet enclosed in an inflated, papery sac 1/3 to 1 inch long. The mature fruiting catkin is similar in appearance to those of hops with a number of sacs in a pendulous series 1¼ to 2 inches long.

Notes:

Ironwood is a common understory tree throughout Minnesota's upland deciduous forest. Highly shade tolerant, it is slow growing in understories where it rarely grows into the canopy. Its branches are often broadly horizontal and retained fairly close to the ground. In open sunnier sites it can grow quite quickly, attaining a height of some stature. While most often it has only a single trunk, its not uncommon to find multi-trunked specimens with a broad, spreading crown. Its name of Ironwood comes from its extremely hard, durable wood. Like our oak species, it typically retains a number of dried brown leaves through the winter months, which is termed marcescent. Ironwood is an excellent small, urban shade garden species.

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More photos

Photos courtesy Peter M. Dziuk taken in Anoka, Hennepin, Ramsey and Wright counties.

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