Carpinus and Ostrya

Posted: July 8, 2015

Let's get to know Carpinus caroliniana and Ostrya virginiana.
Line drawing of Carpinus and Ostrya leaves and nutlets

Line drawing of Carpinus and Ostrya leaves and nutlets

By William C. Paxton, Landscape Architect and Consulting Forester

Don’t worry! I’ll use the common names later (you’ll see why). But for now, we will get to know Carpinus caroliniana and Ostrya virginiana.

If you are searching through the young tree growth of a semi-open understory, and you find what you are almost sure is black birch, but when you give it the definitive smell and taste tests and it’s not there, it is likely Ostrya virginiana. If you are familiar with the Japanese hops, especially the blooms, and you find them on a tree, but they don’t smell like the Rolling Rock Brewery at lunchtime on a hot day, then it is Ostrya. The other names are ironwood and American hophornbeam.

Ostrya is easily distinguished from other trees by its bark which has a “shreddy” appearance, with the bark broken into small, narrow plates which curve away from the trunk. The leaf petioles and undersides of the leaves have a hairy presence.

Carpinus is a very pretty, multi-stemmed tree that grows mostly near or even in wet places, more commonly than Ostrya. It is also found on upland sites. Carpinus is often called blue beech since the leaves resemble American beech, and the bark can appear bluish. The trunk also resembles flexed muscles, hence musclewood is one of its names; another is hornbeam. Both of these trees are in the birch family.

To tell Ostrya from Carpinus is not difficult, because they do not appear similar in form and bark. But, the names assigned to both like hornbeam (derived from a German word meaning tough tree), ironwood, musclewood, blue beech, water beech, and hophornbeam make for confusion. The horticultural trade further adds to the confusion as there are European forms of both species. There is lots of confusion.

Interestingly to me, the leafy bracts of both species collect together in green, leafy, cone-like groupings with a fruit attached one to each bract as a nutlet. The male and female catkins appear on the same tree and they are cross-pollinated by the wind. The nutlets scatter and fall and are eaten by many animals and birds. If not eaten, the seeds will grow to form very pure stands of trees.

There are upright Carpinus trees frequently used in city landscapes, since they never need trimming, and are compact and long-lived. Since they grow slowly, they make successful bonsai specimens. In open grown settings (still a semi-shade environment), they make an attractive landscape curiosity.

If you were to see what you think is a single trunked musclewood in a Pittsburgh city park or in Longwood gardens, with a trunk diameter of over twelve-inches, then it is most likely European hornbeam.

Even though they are Eastern trees, they have been transplanted successfully into every state. The small diameters and the very hard nature of the wood leave them unharvested. If you need a very hard, smooth, long-lasting wood piece, they can’t be surpassed.