Ostrya virginiana (Ironwood)
Also known as: | American Hop-hornbeam, Eastern Hop-hornbeam |
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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): | ![]() |
National distribution (click map to enlarge): | ![]() |
Pick an image for a larger view. See the glossary for icon descriptions.
Detailed Information
Flower:
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.
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:
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.
Twigs are brown to reddish with downy hairs and scattered white lenticils (pores), are often glandular hairy, and become smooth the second year.
Older bark is grayish brown, thin and finely textured with vertical, rectangular plates. Trunks can reach 14 inches diameter.
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
Ironwood tree
Ironwood tree in fall color
Ironwood branches
fruiting branches
hairy new leaves emerging in spring
Photos courtesy Peter M. Dziuk taken in Anoka, Hennepin, Ramsey and Wright counties.
Comments
Have you seen this plant in Minnesota, or have any other comments about it?
on: 2017-04-19 07:13:43
Came home to find a freshly planted ironwood tree on the boulevard (4-18-17, Cooper neighborhood). The city of Mpls is replacing Ash trees infected by the emerald ash borer. This field guide provides a great introduction to a welcome neighborhood addition.
on: 2018-06-18 21:51:01
Near the lake interspersed among the White Pines
on: 2018-08-03 23:22:14
We have ironwood trees in the understory of our 15 acre woods on the lakeshore. Our woods are primarily aspen interspersed with birch, white and red oak, maple, basswood, eastern white pine. I have not observed any large ironwoods but would like to encourage some that we have to grow larger by opening the spaces around them. I find the horizontal branching and fruiting catkins very attractive.
on: 2018-09-21 08:41:27
I would like to post pictures of the most incredible ironwood clusters I have ever seen. Can I get some help to share these?
on: 2018-09-21 17:46:52
Kim, you could post them on the Minnesota Wildflowers Facebook page.
on: 2018-11-08 23:51:33
Occasional in the tall shrub layer in mixed red oak-sugar maple-basswood-aspen forests.
on: 2019-03-07 08:45:12
Understory trees 1-4m tall in upland (hilly) site, 16 of 55-09w, with bigtooth and quaking aspen, balsam fir, spruce. ID based on twigs and persistent dead leaves.
on: 2020-02-13 02:13:58
We have a number of these... love the bark.