BETULACEAE (BIRCH FAMILY) 335 



3. B. nlgra L. (RIVER or RED B.) Tree with greenish-brown somewhat 

 laminate bark and reddish twigs ; leaves acutish at both ends, when young 

 downy underneath ; petioles, peduncles, and thick-cylindric catkins tomentose ; 

 bracts with oblong-linear nearly equal lobes. Banks of streams and in swamps 

 e. of the Alleghenies from e. Mass, to Fhv, thence w. to Tex.; and through the 

 bottom-lands of the Mississippi R. system. 



* * Trees or shrubs with slender cylindric fruiting catkins, their scales readily 

 deciduous ; leaves (of the fruiting branches) with 1 or less pairs of 

 prominent veins. 



+- Wing distinctly broader than the body of the fruit ; trees or stout shrubs with 

 white, whitish, or brown papery bark. 



w Bark dull, chalky- or ashy-white, smooth and close, the layers not readily 

 exfoliating ; staminate catkin usually solitary. 



4. B. populifblia Marsh. (WHITE, GRAY or OLD FIELD B.) Trunk usually 

 ascending, rarely 10 m. high; leaves triangular (deltoid), very taper-pointed 

 (usually abruptly), truncate or nearly so at the broad base, smooth and shining 

 both sides, except for the resinous glands when young, tremulous on very slender 

 petioles ; fruiting catkins slender-stalked, ascending, 1-3 cm. long, 5-7 mm. thick ; 

 the drab or ashy-brown wide-spreading scales 2.5-4 mm. long, their lobes puberu- 

 lent. Poor sandy or rocky soil, commonest near the coast, P. E. I. to Del., w. 

 to L. Ont. 



t-f - Bark lustrous, creamy- or pinkish-white to bronze, freely splitting into 

 paper-like layers ; staminate catkins mostly 2 or 3. 



= Branchlets and leaves strictly glabrous from the first. 



5. B. pndula Roth. (WHITE or CANOE B.) Branches slender and flexuous, 

 often drooping, the branchlets usually verrucose with resiniferous atoms ; leaves 

 glutinous when young, firm, rhombic-ovate to deltoid or broad-ovate, subcuneate, 

 truncate, or subcordate at base, long-acuminate, slender-petioled ; fertile catkins 

 pendulous, 1.5-3 cm. long, 6-9 mm. thick ; the ascending brown or straw-colored 

 scales 3-5 mm. long, glabrous except for the ciliate margin. (B~ rerrucosa 

 Ehrh.) Rocky upland woods and slopes, Que. to Alaska, locally s. to Me., Vt., 

 111., Man., etc. (Eurasia.) A polymorphous boreal species, of which the N. E. 

 phase has recently been designated as B. caerulea Blanchard (BLUE B.). 



= = Branchlets puberulent or pubescent ; young leaves (except in var. minor) 



pubescent beneath. 



6. B. alba L. (PAPER, CANOE or WHITE B.) Branches and branchlets ascend- 

 ing ; resiniferous atoms, if present, mixed with long hairs ; leaves ovate, taper- 

 pointed, from rounded to citneate at base, in maturity 3-6 cm. long, smooth and 

 green above, pale, glandular-dotted, and a little hairy on the veins beneath, sharply 

 and unequally double-serrate; fruiting catkins 1.6-4.5 cm. long, 0.6-1.6 cm. 

 thick, spreading or drooping on slender peduncles ; the mostly ciliate-margined 

 ascending scales 3-7 mm. long. (B. pubescens Ehrh.) Large shrub or medium- 

 sized tree, Nfd. to B. C., s. to N. E., the Great Lake region, etc. (Eurasia.) 

 Passing to the commoner American 



Var. papyrifera (Marsh.) Spach. Usually a larger tree, with mature leaves 

 6-9 cm. long. (B. papyrifera Marsh.) Nfd. to Alaska, s. to Pa., Ind., n. la., 

 Neb., Wyo., and Wash. 



Var. glutindsa (Wallr.) Trautvetter. Branches pendulous ; leaves 3-5 cm. 

 long, pilose on the veins beneath ; catkins on straight peduncles. Wassataquoik 

 Valley, Me. (Eu.) 



Var. cordifblia (Regel) Fernald. Leaves broad-ovate, cordate, pilose on the 

 veins beneath. Cool woods and mte., Lab. and Nfd. to B. C., s. to N. E., L. 

 Superior, la., and westw. Becoming a dwarf shrub on alpine slopes. 



Var. minor (Tuckerm.) Fernald. Stout dwarf shritb; leaves elliptic- or 

 truncate-ovate, glutinous, glabrous, 1.6-4 cm. long; staminate catkin often soli- 

 tary ; fmiting catkins mostly ascending, 1.3-3 cm. long, 0.6-1 cm. thick. CB. 



