BETULACEAE 347 



east to the Rocky ]\Its., south to Mexico, north to Alaska, across the continent 

 to Labrador, thence south to Tennessee. It has a more extensive distribution 

 than any other North American tree. Occurs only in small scattered thickets 

 in California but forming extensive pure forests in the Rocky Mts. Wood 

 burns green. 



Refs. — POPULUS TREMULOIDES Jlichaux, Fl. Bor. Am. vol. 2, p. 243 (1803) ; Sudworth, 21st 

 Rep. U. S. Geol. Sur. pt. .5 (For. Res.), pp. 517, 542 (1900). 



BETULACEAE. Birch Family. 



Wind-pollinated trees or shrubs with alternate simple petioled leaves and 

 caducous stipules. Flowers small, borne in catkins. Staminate catkins elon- 

 gated, pendulous, falling after flowering, the flowers in clusters of 3 in the 

 axil of each bract, consisting of a meml)ranous connnonly 4-parted cal.A-x and 

 1 to 7 (commonly 2 or 4) stamens; bracts dilated above with the apex abruptly 

 upturned, each covering 4 bractlets. Pistillate catkins small, erect, spike-like, 

 the flowers 2 in the axil of each bract, without perianth, consisting of a pistil 

 with 2 styles and a 2-eelled ovary with 1 ovule in each cell. Fruit a very 

 small compressed 1-seeded nutlet which is margined or winged. — Two genera. 

 Bibliog.— Parr_v, C. C, Pacific Coast Alders (Bull. Cal. Acad., vol. 2, p. 351,-1887). 

 Winkler, H., Betulaeea; (Das Pflanzenreich, bd. 4, lief. 61,-1904). 

 Pistillate catkins in clusters, forming in fruit oval or ovoid woody cones which are drooping 



or spreading, their scales obscurely 5-lobed at ajjex; stamens 1 to 7 1. Alxus. 



Pistillate catkins solitary, cylindrical and erect in fruit, falling to pieces when mature, their 



scales plainly 3-lobed at apex ; stamens 2 2. Betula. 



1. ALNUS L. Alder. 



Peduncles branched or forked, bearing a cluster of few to several catkins. 

 Calyx of staminate flower 4 (or 6)-parted; stamens 1 to 7. Pistillate catkins 

 in clusters of 2 to 4. forming woody pendulous cones when mature, the bracts 

 and bractlets united into 5-lobed scales which are persistent on the axis. 

 Nutlet with a narrow acute margin. — North temperate regions, a few ranging 

 in the high mountains to Bolivia; about 18 species, 9 in North America. 

 (Aluus, the ancient Latin name.) 



Catkins appearing in the early autumn as rather conspicuous naked buds, and flowering in the 

 late winter or early spring before the leaves appear; peduncles of the pistillate 

 catkins naked, their branches ^/> inch long or less; sepals 4; stamens 1 to 4. 

 Trees 30 to 80 feet high ; mostly of low altitudes. 



Leaf-margin plane, with small scattered teeth; bracts of staminate catkin obtuse; 



stamens 1 to 3, rarely 4 1. A. rhombifolia. 



Leaf-margin with narrowly revolute edge, rather coarsely toothed; bracts of staminate 



catkins acute or aeutish ; stamens 4, rarely 3 2. A. rubra. 



Shrubs 8 to 15 feet high ; leaf -margin coarsely toothed and again finely toothed ; stamens 



4 or 2 ; high montane 3. A. tenuifolia. 



Catkins appearing in the spring from scaly buds at the same time as the leaves; peduncles 

 of the pistillate catkins leafy (at least at base), their branches Yn to 1 inch long; 

 sepals 6 ; stamens 6 or 7 ; leaf-margin sharply or laciniately toothed ; high montane 

 shr\dj 4. A. viridis. 



1. A. rhombifolia Nutt. White Alder. (Fig. 61.) Tree commonly 30 to 80 

 feet high with whitish or gray-brown bark ; trunks % to 31/2 feet in diameter ; 

 leaves 2 to 4 inches long, minutely pubescent, elliptic and obtuse, or more com- 

 monly oblong-ovate or oblong-rhombic and tapering more or less to the apex, at 

 base broadly wedge-shaped and entire, the remainder of the margin provided 

 with small and more or less unequal glandular teeth; staminate catkins in 



