Betulaceae 103 



often in pairs or in 3\s at the ends of the branches; scales oblong, 

 obtuse in the staminate aments, narrower and more acute in the 

 pistillate, glabrous on the back, crisp hairy on the margin and 

 toward the base, erose above; lower half of the filament densely 

 crisp hairy; capsule lanceolate, covered with straight appressed 

 silky hairs, closely sessile; stigmas sessile, oblong, about twice 

 as long as thick; mature capsule often becoming nearly glabrous. 

 Mostly east of our limits in dry washes. 



Family 17. BETULACEAE. Birch Family. 



Monoecious trees or shrubs, with alternate petiolecl 

 simple Leaves and small flowers in aments. Staminate 

 aments pendulous, with 1-3 flowers in the axils of each 

 bract, consisting of a membranous 2-4-parted calyx or 

 none, and 1-10 stamens. Pistillate aments erect or 

 drooping, spike-like or capitate, their flowers with or 

 without a calyx adnate to the solitary 1-2-celled ovary ; 

 style 2-cleft ; ovules 1-2 in each cell, pendulous. Fruit 

 a small compound or ovoid-globose nut or samara. En- 

 dosperm none ; cotyledons fleshy. 



1. ALNUS Gaertn. Alder. 



Shrubs or trees with dentate or serrulate leaves, and 

 both pistillate and staminate flowers in aments ; the 

 staminate pendulous; the pistillate erect, clustered. 

 Staminate flowers 3-6 in each axil, consisting of a most- 

 ly 4-parted perianth, 1-1 stamens and subtended by 2-4 

 minute bractlets ; ovary 2-celled ; bracts woody, per- 

 sistent, o-toothed or erose. Nut small, compressed, 

 winged or wingless. 



1. A. rhombifolia Nutt. Tree 7-14 m. high, with a light gray 

 trunk; leaves narrowly or broadly ovate to elliptic, 2.5-10 cm. 

 long, irregularly serrulate, somewhat pubescent beneath; stam- 

 inate aments 7-15 cm. long; bracts obtuse; stamens usually 2 



