13(12). Blades 5-8 or 10 cm. long, 5-10 or 12 mm. wide, permanently more or 

 less pubescent 11. S. exigua var. exigiia. 



13. Blades 4—6 or 8 cm. long, 3-5 or 6 mm. wide, soon glabrate to glabrous and 



yellowish green 11. S. exigua var. nevadensis. 



14(C). Blades mostly linear-oblanceolate, pubescent while young, becoming 

 glabrous, densely glaucous and veiny; distribution mostly in moun- 

 tain canyons 17. 5. lasiolepis var. Bracelinae. 



14. Blades narrowly elliptic to oblanceolate, densely pubescent while young, more 



thinly so and somewhat rugose in age; distribution in low or upland 



prairies or open wasteland eastward 



23. S. humilis var. rigidiuscula. 



Key Based on Floral Characters (for Oklahoma and Texas species) 



1. Flower scales yellowish, slowly deciduous; aments leafy-pedunculate (2) 



1. Flower scales blackish, persistent; aments precocious, sessile or subsessile (11) 



2(1). Aments only one per peduncle, mostly coetaneous, occasionally subpreco- 

 cious; capsules always glabrous (in Texas) (3) 



2. Aments (especially staminate) 2 to 4 per peduncle, the supernumerary later, 



at base of the first, serotinous; stamens 2; ovaries (sometimes) and 

 capsules (less frequently) more or less hairy while developing (8) 



3(2). Stamens 2 (occasionally 3 or 4); maturing fruiting aments 7-10 mm. 

 wide; trees introduced 6. S. fragilis. 



3. Stamens 3 to 7 or 8; trees native (4) 



4(3). Fruiting aments. (mature) 10-15 mm. wide; capsules 4-5 or 6 mm. long; 

 pedicels 1-2 mm. long (5) 



4. Fruiting aments (mature) 15-20 mm. wide; capsule 5-6 or 7 mm. long; pedi- 



cels 1.5-3 mm. long (7) 



5(4). In the Texas Plains Country (Panhandle) and western Trans-Pecos, west- 

 ward 4. S. amygdaloides. 



5. In Texas and/ or Oklahoma east of the above regions (6) 



6(5). Capsules ovoid to ellipsoid, sculptured; stipules glandless; lacking a minia- 

 ture shoot from the axis of the top peduncle leaf 



2. S. Humholdtiana. 



6. Capsules ovoid-conical, unsculptured; stipules more or less glandular; often 



producing a shoot from the axis of the top peduncle leaf 



1. S. nigra. 



7(4). Capsules mostly 5.5-6.5 mm. long 3. 5". Gooddingii var. variabilis. 



7. Capsules mostly 4.5-5.5 mm. long 9. S. caroliniana. 



8(2). Aments 1-1.5 cm. long, crowded near the tips of twigs 



10. 5. taxifolia. 



8. Aments 3-6 or 8 cm. long, scattered along the twigs (9) 



9(8). Capsules 5-6 or 7 mm. long; aments to 15 mm. wide 



11. S. exigua and vars. 



9. Capsules 8-9 or 10 mm. long; aments to 20 mm. wide (10) 



10(9). Capsules thinly silky to glabrous when young, glabrous when mature 



12. S. interior var. interior and S. interior var. pedicellata. 



10. Capsules densely white-hairy while young, gray-hairy when mature 



12. S. interior var. angustissima. 



11(1). Aments 8-12 mm. wide; capsules 4-5 mm. long, glabrous 



17. S. lasiolepis var. Bracelinae. 



11. Aments 15-20 mm. wide; capsules 7-9 mm. long, pubescent 



23. S. humilis var. rigidiuscula. 



ISA 



