Carya

1. Bud scales valvate, yellow (from dense granules), the 2–3 pairs leaving well-separated glabrous scars; fruit small (1.8–2.7 cm long, including beak), the husks with prominent ridges or low wings at sutures above, not splitting all the way to the base, thin (ca. 1–1.5 mm thick); leaflets 7–9, never only 5, their margins glabrous or nearly so.

C. cordiformis

1. Bud scales imbricate, at most with scattered yellow granules, more than 6, the scars crowded, usually ciliate when fresh; fruit various but scarcely if at all ridged at sutures and if as small as in C. cordiformis, then the husk usually thick and/or splitting all the way to the base (only in some forms of C. glabra, with 5–7 leaflets, is the fruit both small and with husks splitting only halfway to the base); leaflets 5–9.

2. Leaflets consistently 5, ciliate when young, retaining a dense tuft of small hairs on one or both sides of each tooth just below its apex (these tending to wear off on some leaflets by fall); fruit 2.1–4.1 (–4.5) cm long, the husks 3–10 (–12) mm thick, splitting all the way to the base at maturity; bark “shaggy.”

C. ovata

2. Leaflets 5–9, if 5 not ciliate, and never with dense tufts on teeth; fruit and bark various.

3. Leaflets 5 (–7), glabrous or glabrate beneath or rarely pubescent especially on veins; larger winter buds (terminal or pseudoterminal) 5–10 mm long; rachis of leaves often glabrous; fruit 1.6–3.2 (–3.5) cm long, the husks 0.6–4 mm thick.

C. glabra

3. Leaflets 7 (–9) (sometimes a few small leaves with only 5), ± pubescent beneath; larger winter buds (6–) 11–20 mm long; rachis of leaves glabrate to pubescent; fruit (3.5–) 4–6 cm long, the husks 6–11 mm thick.

C. laciniosa

All species found in Carya

Carya cordiformisBITTERNUT HICKORY 
Carya glabraPIGNUT HICKORY 
Carya laciniosaSHELLBARK HICKORY, KINGNUT HICKORY 
Carya ovataSHAGBARK HICKORY 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 29, 2017. http://michiganflora.net/genus.aspx?id=Carya.