3(1). Leaves rounded to truncate or subcordate at base, often somewhat lobu- 

 late; stamens 4 3. A. incatia. 



3. Leaves typically cuneate at base, seldom lobulate; stamens 1 to 3 (usually 2) 

 4. A. oblongifolia. 



1. Alnus semilata (Ait.) Willd. Smooth alder. Fig. 394. 



Spreading or laxly ascending deciduous shrubs or small trees to 5 m. or more 

 tall, the main stem to 15 cm. in diameter; bark of trunk smooth, light grayish- 

 brown to reddish-brown or blackish-gray, with dark lenticels; leaves with petioles 

 to 15 mm. long, obovate to obovate-elliptic or elliptic, narrowly to broadly 

 cuneate at base, rounded to acute at the apex, to 1 dm. long and 6 cm. wide, 

 the margins simply serrulate or rarely somewhat undulate, the expanding leaves 

 glutinous and aromatic; aments usually formed in the fall and expanding in early 

 spring; staminate aments pendulous, in clusters of 3 to 5, each of the bracts sub- 

 tending 3 flowers; staminate flowers with a minute 4-parted calyx and 4 stamens 

 with undivided filaments; pistillate aments in clusters of 2 or 3, ovoid to ellip- 

 soid, 1.5-2 cm. long, the fleshy cuneate bracts 3-4 mm. long, each subtending 

 2 flowers and a group of 4 tiny scalelets adherent to the bracts of the aments; 

 fruit a persistent semiwoody strobile, each cuneate to cuneate-obovate truncate 

 or lobulate scale bearing 2 to 4 compressed laterally winged nutlets. 



Along streams and in swamps and boggy situations, in s.e. Okla. (McCurtain 

 and Pushmataha cos.) and in e. Tex., Mar.-Apr.; from N.E., s. to Fla. and Tex., 

 Okla., Mo., Ind. and O. 



Often confused with the eastern A. rugosa (Du Roi) Spreng., whose bark has 

 linear, whitish lenticels. 



2. Alnus maritima (Marsh.) Nutt. Fig. 394. 



Shrub or small tree to about 10 m. tall; bark reddish-brown; branchlets at first 

 pubescent, soon glabrate; leaves oblong-elliptic to obovate, obtuse to acute or 

 short-acuminate at apex, serrulate with low distant ascending or incurved teeth, 

 broadly cuneate to a long petiole, to 10 cm. long and 5 cm. wide, dull green and 

 glabrous beneath; aments expanding in late summer; pistillate aments 2 or 3 in a 

 raceme, oblong-ovoid, 2-3 cm. long, 1.5-2 cm. thick, maturing the 2nd year; 

 bracts with depressed and broad terminal lobes; nutlets 3-4 mm. long, thin- 

 margined. 



Banks of streams and ponds, and in wet woods in s.e. Okla. (Johnston and 

 Pontotoc COS.); also Del. and Md. 



3. Alnus incana (L.) Moench. Thin-leaf alder. 



Shrub or small tree to about 10 m. tall, often forming thickets; bark grayish- 

 brown to reddish; leaves ovate-oblong to broadly elliptic, usually 5-10 cm. long, 

 rounded to truncate or subcordate at base, rounded to obtuse or somewhat acute 

 at apex, sinuate and serrate-denticulate on margins, dark-green and glabrous to 

 pubescent above, pale and usually heavily pubescent beneath; staminate aments 

 to 10 cm. long; stamens 4; pistillate aments ovoid-ellipsoid, 8—12 mm. long, with 

 stout peduncles; scales 3-lobed at apex; nutlets without a true wing. A. tenui folia 

 Nutt. 



In bogs, about ponds and lakes, on stream banks and in wet woodlands, in 

 N.M. (Rio Arriba, Sandoval, San Miguel and Taos cos.) and Ariz. (Apache, 

 Graham and Pima cos.); Minn, and N.D. to B.C., N.M., Ariz, and B. Calif. 



Our plant is referred to ssp. rugosa var. occidentalis (Dippel) C. L. Hitchc. 

 by recent authors. 



4. Alnus oblongifolia Torr. New Mexican alder, Arizona alder. 



Tree to about 10 m. tall, with a trunk to 2.5 dm. in diameter; bark thin, 

 light-brown tinged with red; branches reddish-brown; leaves ovate-oblong to 



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