Carpinus caroliniana – American Hornbeam

A very large C. caroliniana showing a fluted trunk at the Bill Mason Centre

In the Betulaceae (Birch) family, American Hornbeam (also called Blue Beech, Musclewood, and sometimes Ironwood) is a small, understory tree that often forms multi-trunked colonies in moist, rich forest conditions in the dappled shade of larger deciduous hardwood trees.  It has an upright shape and an elegant, open canopy of fine twigs that show its alternate leaf structure.  Bark is its main distinguishing feature: smooth, grey with a blue undertone, angular, and “fluted” resembling a sinewed human arm.  The buds are reddish brown and pressed against the twig in winter. Leaves are dark green, double-toothed, and ovoid.  Fall colour is a lovely orange against the bluish bark. Hornbeam is slow growing and not a prolific species; it’s found in limited numbers near the edge of ephemeral woodland ponds and damp areas.  Trees do not regularly flower and set seed, but seem to do so when they get more light beside forest clearings.  A tree spreads locally by forming colonies with connected root systems.  Hornbeam should be more widely available as a landscape tree for shaded lots. 

Hornbeam’s twigs, buds, and leaves are similar to the very common and widespread Eastern Hophornbeam (Ostrya virginiana) called Ironwood, which is easily distinguished by its shaggy, shredded bark and ability to grow in dry, rocky conditions.
 
A good place to see this tree is at Fitzroy Provincial Park, which has the largest number of Hornbeams along the Carp Trail and scattered throughout the Pine Grove campground.  Also see the Bill Mason Centre off Dunrobin Road, which has some particularly large trees, and on the Crazy Horse Trail in the Carp Hills near the beginning of the trail.
 
Selected photographs with location coordinates in iNaturalist:
 
http://www.inaturalist.org/observations/2712016  Shows its lovely orange fall colour, in a graveyard near Burritt’s Rapids.
http://www.inaturalist.org/observations/2568265  Very large specimen showing the sinuous, smooth trunk, near Russell.
http://www.inaturalist.org/observations/5222122  Photo showing the alternate branching and reddish brown buds.
http://www.inaturalist.org/observations/5139318  Leaf photos showing ragged, double-tooth edge, at McCarthy Woods in Ottawa.
http://www.inaturalist.org/observations/2876130  Very large specimen at the Bill Mason Centre in West Carleton.
http://www.inaturalist.org/observations/2659701  Shows a typical colony formation, in the Carp Hills.
http://www.inaturalist.org/observations/5297027  Shows one of the many colonies at Fitzroy Provincial Park, this one at the Pine Grove campground.