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Ostrya virginiana (Mill.) K. Koch. Ironwood
Also known as: Hop-hornbeam.
Habitat
Ironwood occurs naturally in the southern half of New Brunswick. It usually grows as scattered individuals among sugar maple, beech, yellow birch, and white ash on rich, well-drained sites, and often in the understorey, as it is a relatively small, very shade-tolerant species.
Form
Ironwood rarely grows taller than 13 m or to stem diameters greater than 30 cm. It usually produces an upright stem that is visible almost to the top of the crown. The crown is rounded and the branches may spread widely, especially when grown in the open.
Morphology
The leaves are deciduous, simple, alternately arranged, and tend to be larger nearer the ends of the shoots. Each leaf is short petioled, oval to elliptic, tapered at both ends or sometimes narrowly rounded or indented at the base, and sharply toothed around the margin, with teeth at vein ends only slightly larger than intervening teeth. The secondary veins are nearly straight and parallel and some near the middle are distinctively forked. Undersurfaces are somewhat hairy, especially when the leaves are young.
The twigs are slender, slightly zigzagged, and reddish brown with inconspicuous lenticels. All buds are lateral, thus the end bud is a pseudoterminal bud with both a twig scar and a leaf scar at its base. The buds, except the end bud, are angled widely from the twig. They are greenish brown, plump, pointed, and have overlapping scales, each of which is striated along its length. Leaf scars are narrowly oval and each carries three vein scars. Many twigs carry preformed male catkins at their ends over winter. These are usually borne in threes, sideways, at an angle away from the direction in which the supporting shoot has grown, and each is 8—15 mm long.
In the spring, the male catkins elongate to 3—4 cm and hang down as their flowers emerge from below each bract. This happens as the new shoots and preformed leaves are expanding. At the ends of some of these new leafy shoots, preformed female catkins, that were hidden in the buds, extend. Fruits develop from the female flowers along these catkins. By fall, these become sharply hairy, yellow-brown sacs, 15—25 mm long, arranged in hanging catkins. Each sac contains a small, dark brown nut that contains a seed.
Ironwood bark is smooth, dark grey, with small horizontal flecks when young. When older, it is greyish brown and divided into narrow vertical strips that have loose, scaly surfaces. The scales peel away or are loose at both ends, and are easily rubbed off, revealing a reddish-brown color beneath.
Notes
Ironwood, as the name implies, is one of the hardest, heaviest, and toughest of our native diffuse-porous woods. However, it is not much used because the trees are small and occur relatively infrequently. The wood makes good sleigh runners and tool handles.
The bark of young ironwood trees is not distinct and may be confused with yellow birch (Betula alleghaniensis Britt.).
In addition, their leaves are similar. Differences between the leaves of the two species occur in the degree to which features are displayed. The tendency for forking of the middle secondary veins occurs more strongly in ironwood and involves more of the veins (the forking is best seen on the undersides of the leaves). Differences between larger and smaller adjacent teeth around the margins tend to be greater in yellow birch than in ironwood, i.e., yellow birch leaves are more conspicuously “doubly serrate.” Neoformed leaves near the ends of the strongest shoots of yellow birch are copiously velvety hairy on both surfaces, leaves of ironwood are never like that. Note that mature preformed leaves of yellow birch (from short shoots or from the basal parts of long shoots) have no hairs on their surfaces, but those of ironwood have some hairs on undersurfaces. Ironwood leaves are usually thinner than those of yellow birch.