Carya cordiformis – Bitternut Hickory

Bitternut Hickory at Stony Swamp

At its northern range in the Ottawa Valley and west Quebec, Bitternut Hickory is a large, stately tree distributed across the Ottawa area in woodlands and urban natural areas.  It is the only native, naturally occurring hickory that grows this far north.  (One exception is a singular population of Shagbark Hickory (C. ovata) in Aylmer, Quebec.)  It should be more widely planted in parks and large properties for its elegant form and its yellow fall colour.  It is also a primary host plant for many caterpillars (e.g. the Hickory Tussock Moth) and provides an additional mast crop for mammals despite being quite bitter.

Bitternuts prefer moist, deep, slightly acid soils, but can grow in dry, upland and alkaline sites.  Like all nut trees, it needs full sun to thrive.

Sulfur bud.

Bitternuts are one of easiest deciduous tree to identify without leaves due to their sulfur yellow buds, which are unique among the woody plants in our area. Some Bitternuts are also afflicted with black galls, which are visible high in the canopy growing on the trunk and branches.  The galls are fungi from the genus Diaporthe (formerly Phomopsis), a sac fungus.  They can be as large as softballs, but don’t seem to harm the tree.

Other distinguishing characteristics:

Bitternut Hickory bark at the Kanata Beaver Pond.
  • Oblong, spreading crown when grown in the open, but otherwise narrow and tall reaching for the sunlight in forest sites.  Often with a long, branch-free trunk that bifurcates to two main branches.
  • Bark – smooth when young, then lightly furrowed, often with either yellow cast or greenish-blue cast.
  • Alternate, pinnate, compound leaves, usually 7 to 9 leaflets, with a terminal leaflet; leaves lanceolate, margins toothed, tip pointed.  New growth is coppery or red, turning bright green.
  • Trees bloom in mid- to late May.  The yellow-green flowers are separate sexes on the same tree.
  • Fall colour – bright, clear yellow.

 

Hickory Nuts in early August.

In heavy mast years, trees will rid themselves of hard, bright green, unripe nuts in August.  Ripe nuts drop in September.
They consist of four sections with a terminal beak, and are light yellow-green to yellow-tan in colour with a pleasant lime/bergamot smell.  When ripe, the nuts can be more easily peeled to expose small roots growing at the base.

Bitternut Hickories can be found in most mesic woodlands in the Ottawa area.  Sites with large, accessible populations are the Beaver Pond trail and Trillium Woods in Kanata, Stony Swamp, and Carlington Woods.

Selected photographs with location coordinates in iNaturalist:

https://www.inaturalist.org/observations/16482534 – seedling in the Carp Hills.
https://www.inaturalist.org/observations/19046263 – large galls in Lanark County.
https://www.inaturalist.org/observations/31915391 – compound leaves, bark, nuts on a island in Big Rideau Lake.
https://www.inaturalist.org/observations/22982263 – drooping male flowers at Carlington Woods.
https://www.inaturalist.org/observations/23485109 – female flowers at Reveler CA.
https://www.inaturalist.org/observations/24566327 – large hickory at Carlington Woods.
Fungal galls on Hickory at Stony Swamp.
Bitternut Hickory male flowers at Reveler Conservation Area.
Bitternut Hickory female flowers (O. Clarkin).