Flower:

Male and female flowers are borne separately on the same branch (monoecious). Male flowers are in clusters called catkins, 1½ to 4+ inches long, pendulous in flower, in groups of 3 in the leaf axils of 1 year old branchlets, sometimes at the base of the current year's new branchlets. Flowers are yellowish-green with up to 10 hairy stamens.

Female flowers are tiny, clustered 2 to 4 at the tip of this year's new branchlets. Flowers have a stout, yellowish to green, cup-shaped ovary covered in tiny scales, and green stigma at the top.

Leaves and bark:

Leaves are alternate, 8 to 16 inches long, compound usually with 7 or 9 leaflets, occasionally 11, rarely 5 or 13. Leaflets are somewhat variable in shape, typically narrowly elliptic when mature but often proportionately broader and widest near the tip (obovate) when young. Leaflets are 1 to 8 inches long, ½ to 2½ inches wide, finely toothed around the edges, stalkless or nearly so, tapering at the base, tapering to a pointed tip, sometimes abruptly so. The leaflet pair at the tip is largest, becoming smaller as they descend the stalk. The upper surface is dark green and minutely hairy along the veins, the lower is paler in color (though may be bronze-tinged when young), hairy along the veins and variably covered in tiny, round scales, mostly near the edges and more densely scaly at the leaflet tip and base. The compound leaf stalk is green and hairy, more densely so on the upper stalk. Hairs and scales may persist or wear off. Leaves turn golden yellow in fall.

Buds are distinctly yellow to yellow-brown and covered in tiny scales; the terminal bud is oblong and may be ½ inch long. New twigs are brown and hairless with scattered pale lenticels (pores).

Older bark is gray to gray-brown, smooth but developing vertical splits showing an orange-brown inner-bark. These become flat plates and narrow, shallow furrows with age. Trunks can reach up to 20 inches diameter at breast height (dbh).

Fruit:

Fruit is oval to round, about 1 inch diameter, the outer husk relatively thin, rough-textured, green, with 4 distinct ridges that extend from the tip to half or more the length, but not all the way to the base. Inside is a bitter nut with a hard shell.

Notes:

Bitternut Hickory is an occasional to common tree found in hardwood forest, primarily in the southeast quadrant of Minnesota with scattered populations as far north as Itasca County, where it reaches the northwest edge of its range. The leaflets that become smaller towards the base of the compound leaf resemble those of the related Juglans (Black Walnut, Butternut) species as well as those of the unrelated Fraxinus (Ash) species, but Juglans have sticky hairs and more numerous leaflets, and Fraxinus have rather different flowers and fruits, and its leaflets are often short-stalked. But Bitternut Hickory may be more easily distinguished by the yellow buds, which can be seen most any time of year, and the scaly leaves and round fruits with 4 prominent ridges. Shagbark Hickory (Carya ovata) also has similar fruit and leaves, but almost always has 5 leaflets in a compound leaf (rarely 3 or 7), and the fruit is sweet and larger (to 1½ inches) with a thick husk that lacks the distinct ridges, but has 4 seams that go all the way to the base. And, of course, shaggy bark on mature trees. Shagbark and Bitternut Hickory have been reported to hybridize with each other, but no hybrids have been reported in Minnesota.