B. Leaves linear or linear-oblong, acute, almost sessile, subentire to remotely and 



irregularly denticulate (8) 



C. Leaves linear-oblong or linear-oblanceolate, 5-10 cm. long, distinctly petioled, 



entire to undulate-serrate, glaucous on lower surface, more or less 

 pubescent (14) 

 1(A). Leaves green beneath, linear-lanceolate, acuminate (2) 



1. Leaves glaucescent to glaucous beneath (5) 



2(1). Twigs all yellowish; blades narrowly lanceolate 



3. S. Gooddingii var. variabilis. 



2. Twigs brown to blackish (seasonal somewhat yellowish) (3) 



3(2). Capsule ovoid to ellipsoid, sculptured; leafy peduncle without a miniature 



shoot from the axis of its uppermost leaf; stipules glandless 



2. S. Humboldtiana. 



3. Capsule ovoid-conical, unsculptured; leafy peduncle often producing a minia- 



ture shoot from the axis of the uppermost leaf; stipules more or 

 less glandular (4) 



4(3). Petioles short, averaging about 6 mm. long, brownish, pubescent; blades 

 broader, less narrowed at base 1. 5. nigra var. nigra. 



4. Petioles longer, averaging about 8 mm. long, yellowish, glabrous; blades nar- 



rower, more narrowed at base 1. S. nigra var. Lindheimeri. 



5(1). Petioles with glands near leaf base; blades lanceolate, coarsely crenate- 

 serrate, dark-green above, glabrous 6. 5. fragilis. 



5. Petioles without glands near leaf base (6) 



6(5). Twigs brownish, often pubescent; blades linear- to narrowly lanceolate, 

 long-acuminate, often pubescent, dark-green above (5. longipes var. 

 Wardii) 9. S. caroliniana. 



6. Twigs yellow or yellowish, glabrous; blades yellowish-green above, glabrous 



(7) 



7(6). Blades lanceolate or somewhat ovate-lanceolate; aments lax 



4. S. amygdaloides var. amygdaloides. 



I. Blades linear-lanceolate or lingulate-lanceolate; aments denser 



4. 5". amygdaloides var. Wrightii. 



8(B). Blades yellowish-green, somewhat translucent, glabrous (more or less 

 thinly hairy while developing) (9) 



8. Blades green, more opaque, silvery-silky or more or less gray-pubescent (10) 



9(8). Blades 5-10 or 12 cm. long, 5-10 mm. wide.... 12. S. interior var. interior. 



9. Blades 5-8 or 10 cm. long, 2-5 mm. wide 12. S. interior var. pedicellata. 



10(8) . Blades silvery-silky, at least until full-size (11) 



10. Blades more or less gray-puberulent or gray-pubescent (12) 



11(10). Blades 6-10 or 12 cm. long, usually sharply denticulate, the hairs per- 

 sisting beneath (especially on midrib) 



12. S. interior var. angustissima. 



II. Blades 5-8 cm. long, mostly subentire, the hairs persisting on both surfaces.... 



11. S. exigua var. stenophylla. 



12(10). Blades only occasionally more than 4 cm. long and 4 mm. wide, usually 



crowded, yewlike, pubescent, often becoming glabrate 



10. S. taxifolia. 



12. Blades only occasionally less than 5 cm. long, 5 mm. wide, not yewlike, 

 pubescent or glabrous (13) 



753 



