106 American Midland Naturalist Monograph No. 2 



[C. olivaeformis Nutt.; C. pecan (Marsh.) Engler SC Graebn.} 



C. illinoensis (Wang.) K. Koch 



2. Leaves glabrous; staminate catkins in threes on a common peduncle; nut 



sharply angled; seed very bitter; bark of trunk exfohating in long strips; 



river bottoms, rare, s. III. Mar.-Apr. Water Hickory. Bitter Pecan 



C. aquatica (Michx. f.) Nutt. 



1 . Leaflets 5-9 (or rarely 11). 



3. Bud-scales mustard-yellow, 4 or 6, valvate in pairs; leaflets lanceolate, 



acuminate, sessile or nearly so, the lateral ones somewhat falcate; stam- 

 inate catkins in threes on a common peduncle; nut smooth, globose, 

 acute, thin-shelled, whitish; seed becoming bitter; bark of trunk not 

 exfoliating, gray, close, smooth or ridged, woods, common. May- June. 

 Bitternut Hickory. Yellowbud Hickory. [C. atnara Nutt.; Hicoria 

 minima Britt.} C. cordiformis (Wang.) K. Koch 



3. Buds not yellow; bud-scales 6 or more, imbricated. 



4. Leaflets usually 7 (rarely 5 or 9) . 



5. Leaflets at maturity glabrous or nearly so; young twigs, and rachises 

 of mature leaves glabrous; terminal bud 5-10 mm. long; bark close 

 or scaly; nut 1.5-3 cm. long, compressed, round at the base; woods, 

 centr. and s. III. May-June. [C. microcarpa Nutt.] Small-fruited 

 Hickory C. ovaUs (Wang.) S.irg. 



5. Leaflets at maturity pubescent beneath; terminal bud 1-2.5 cm. long. 



6. Rachis and lower surface of mature leaflets stellate-tomentose; 



bark rather close, ridged; nut 1.5-3 cm. long, rounded at base; 



seed somewhat astringent; woods. May- June. [C. alba (L.) K. 



Koch, not Nutt.} Mockernut. Bigbud Hickory 



C. tomentosa Nutt. 



6. Rachis and lower surface of mature leaflets short-pubescent espe- 

 cially along the veins; bark shaggy; nut 3-6 cm. long, cuneate at 

 base; seed sweet, not astringent; woods, not common. Big Shag- 

 bark Hickory C. lacinioia (Michx. f.) Loud. 



4. Leaflets usually 5 (rarely 3 or 4) . 



7. Terminal bud 1-2 cm. long, grayish-tomentulose; twigs stout; leaflets 

 more or less pubescent beneath, at least on the veins; dry husk of 

 fruit 4-10 mm. thick; bark shaggy; woods, common. [C. alba 

 Nutt.] Shagbark Hickory C. ovata (Mill.) K. Koch 



7. Terminal bud 5-10 mm. long, glabrous or nearly so; twigs slender; 

 mature leaflets glabrous except on the veins; bark shallowly ridged, 

 tight; dry husk of fruit 1-3 mm. thick; woods, not infrequent. Pig- 

 nut Hickory C. glabra (Mill.) Sweet 



41. Betulaceae Agardh. — Birch Family 



I. Nuts small, compressed and often wmged, without an involucre, borne in catkins; 



staminate flowers consisting of 2-4 stamens and a 2-4-parted calyx. 



2. Scales of the pistillate catkins 3-lobed, deciduous (sometimes only tardily so) ; 



stamens 2, bifid; leaf-buds sessile, with 3 or more scales; bark often peeling 



horizontally 1 . Be tula 



