The Friends of the Wildflower Garden, Inc.

Trees & Shrubs of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States


Common Name
Hophornbeam (Ironwood, Eastern Hophornbeam; American Hophornbeam, Leverwood)


Scientific Name
Ostrya virginiana (Mill.) K.Koch


Plant Family
Birch (Betulaceae)

Garden Location


Prime Season
Spring flowering - Autumn seed pods


Tree Age Calculator


Hophornbeam is a slow growing tree of medium height (20 to 50 feet), usually never more than one foot in diameter, with a tapering crown.

Leaves are alternate, oval or elliptical with a distinctive double sawtooth edge. Surfaces are smooth but there is fuzziness along the mid-vein and on the stalk (Petiole). The leaf tip is pointed, usually abruptly so. In Minnesota's climate dry brown leaves tend to stay on parts of the tree into the winter months.

Bark is grayish-brown with vertical strips that usually have a slight spiral twist off the vertical. These strips flake off easily. Young stems will be smoother with a reddish brown color.

Twigs are reddish brown, varying from having some fine hair to mostly smooth, with plump buds that have about 6 grooved scales. Bud scales have a darker band near the scale margins.

Flowers: Flowers are separate (monoecious). Female flowers (pistillate) are light-green and catkin-like, about 1/2 inch long with protruding reddish styles. The female flowers develop at the tip of the prior years wood, just as the leaf buds are opening. Male flowers (staminate) are reddish-green catkins at the end of different branches of the prior years wood, usually in hanging clusters of three. Small green bracts are at the base of the catkin. These male catkins actually develop in the fall, overwinter, and then enlarge in the spring. Catkins are also referred to as 'aments'.

The fruit develops in a white to yellowish hanging cluster of small sacs, inflated at first and then maturing to a flattened brown cluster of sacs, each sac containing a small brown nutlet that has a fine surface reticulation. These clusters may persist through the winter. Trees are usually 25 years old before bearing significant fruit.


Habitat: Hophornbeam will grow in partial shade but not dry soils. It is usually found as an understory tree at the edges of woods where it leans to reach sunlight. In the open, it will develop into a nice rounded tree. Young trees do not produce fruit. Seeds require lengthy stratification to break their double dormancy.

Names: The common name of Hophornbeam derives from the seed capsules resembling hops and the wood being as hard as the Hornbeam. The Ironwood name is from the hardness of the wood as anyone who has used an ax on it will acknowledge. The common name 'ironwood' however, is applied to many different tree species that have dense hard wood, in this genus and in others. There are several different species in the Ostrya genus, and unfortunately, all with some use of "Hophornbeam" in their common name. That's why scientific names are best used. As to the name 'Leverwood', Michaux explains in the notes at the bottom of the page. The genus name, Ostrya, is from the Greek word for this tree - ostrys. The species name, virginiana, means 'of Virginia' the state named for England's Queen Elizabeth I, and where the tree was first classified.

The author names for the plant classification are as follows: First to publish was ‘Mill.’ which refers to Philip Miller, Scottish botanist (1691-1771) who was chief gardener at the Chelsea Physic Garden and wrote The Gardener's Dictionary which ran through 8 editions. He was considered “the accurate Miller,” the most famous gardener and nurseryman of the day. The book spread the idea of gardening among the middle class who could now enjoy what was formerly the province of the wealthy. His prime source for North American plants was John Bartram. Miller's work was amended by ‘K.Koch’ who was Karl Heinrich Emil Koch (1809-1879), German botanist, Professor of Botany, first professional horticultural officer in Germany, plant collector in and near Asia Minor.

In earlier years this species was classified as Carpinus virginiana

Comparisons: There are similarities in leaf and catkins with Muscle-wood (American Hornbeam, Carpinus caroliniana), but that tree has smooth bark and the fruit is developed in a cluster of large bracts, rather than in inflated sacs. During the winter, many species in the Birch family have the new male catkins at the tips of the twigs, but the bark of O. virginiana is distinctive.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

Ironwood tree Ironwood Bark Ironwood leaf

Above: 1st photo - The shape of a young tree in mid-summer. 2nd photo - The bark has vertical strips that have a slight twist off the vertical. 3rd photo - The identifying double sawtooth edge of the leaf. Also note that the foreground leaf has a pointed tip, but not abruptly tapered like the one behind and to the left which is the more typical tip shape.

Below: 1st photo - Male catkins occur at the end of a branch usually in groups of three. 2nd & 3rd photos - Twigs are reddish brown, with some fine hair or mostly smooth with plump buds that have about 6 grooved scales.

Ironwood male flower Ironwood twig Ironwood twig

Below: Seed development

Below: 1st photo - Female flowers develop in short green catkin-like aments. 2nd photo - The young seed capsules appear inflated like small balloons. 3rd photo - capsule sections have flattened out

Ironwood Female catkin Ironwood early seed capsule Ironwood Seed capsule

Below: 1st photo - In late summer, the mature capsules have turned brown with a seed is maturing inside each. 2nd photo - Each sac of the seed pod (one shown) has a single ovate seed that is brown at full maturity. 3rd photo - Seed capsule from the prior year still on the tree as new leaves develop in May.

Ironwood mature seed capsule Ironwood seeds Ironwood prior year seeds

Below: Two images of mature trees with formed seed capsules.

full tree full tree


Notes: This plant is indigenous to the Garden area. Eloise Butler catalogued it on April 29, 1907. Garden Curator Susan Wilkins added additional plants in 2008 and 2015. It is native to much of Minnesota except counties in the SW, the upper NW and the Arrowhead region. Its range in North America extends from the great plains area (Manitoba south to Texas) eastward to the coast.

O. virginiana is the only species of Ostrya found in Minnesota. There are two other species of Ostrya in North America, both are found only in the Southwestern U.S.

Uses: The hardness of the wood makes it a choice for durable items such as tool handles, wear surfaces and fence posts. The Janka rating is 1780 making it the hardest tree wood native to Minnesota and just under Hickory at an 1820 rating. Red Oak by contrast is 1290. World-wide this scale tops out with Lignum Vitae at 4500.

Hutchins reports use in folk medicine of the bark and inner wood of the tree particularly for fever, nervous disorders and stomach upset. (Ref. #12). Densmore reports that the Chippewa used the wood of the branches, cut into small bits and boiled to make a decoction taken internally to treat Kidney trouble. (Ref. #5).

Botanist Francois Michaux (son of Andre) wrote in his North American Sylva of 1819-1821: "In the district of Maine it is called Lever Wood, and by the French of Illinois Bois dur (hard wood). In the northern states, and particularly in the District of Maine, the Iron Wood is used for the levers with which the trees felled in clearing the ground are transported to the piles on which they are consumed. Near New York, brooms and scrubbing-brushes are made of it, by shredding the end of a stick of suitable dimensions. Though its uses are unimportant, they might probably be more diversified; it seems well adapted for mill-cogs, mallets, etc."

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

graphicIdentification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.