This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Trees or shrubs, with single-scaled buds, the scales with an adherent membrane within, mostly narrow and short-petioled leaves and persistent or early deciduous broad or minute stipules. Bracts of the aments entire. Disk gland-like, small or minute. Staminate aments dense, erect, spreading or drooping. Staminate flowers with 1-10, mostly 2, stamens, their filaments distinct or sometimes united. Pistillate aments usually erect or spreading. Ovary sessile or short-stipitate. Style short or filiform. Stigmas 2, entire or 2-cleft. Capsule mostly 2-valved. [Name ancient.]
About 200 species, of wide geographic distribution throughout the north temperate and arctic zones, a few in the southern hemisphere. Besides the following, some 60 others occur in the northern and western parts of North America. Many hybrids are known. Type species: Salix alba L.
A. Trees, or large shrubs mostly more than 3° high (no. 24 smaller).
1. Capsule glabrous, or in nos. 7 and 8, silky-pubescent, not tomentose.
Pedicels slender, 3-5 times as long as the gland.
Petioles and stipules without glands.
Leaves narrowly lanceolate; petioles very short.
Leaves broadly lanceolate; petioles slender.
Leaves whitish beneath.
Petioles and stipules with prominent glands.
Summer-fruiting; leaves green beneath.
Autumn-fruiting; leaves pale beneath.
Pedicels about twice as long as the gland.
Filaments hairy at the base; bracts caducous, yellow.
Pedicels in fruit 1-3 mm. long; native shrubs or small trees.
Leaves entire, finely and almost permanently silky.
Leaves denticulate, coarsely silky when young, glabrate in age.
Pedicels in fruit less than 1 mm. long; large introduced trees.
Branches not drooping; leaves lanceolate.
Branches drooping; leaves linear-lanceolate.
Filaments glabrous; bracts persistent.
Mature leaves glabrous.
Length of leaf-blade less than three times its breadth.
Mature leaves thin, dull.
Mature leaves thick, firm, dark green and shining above.
Length of leaf-blade three times its breadth or more.
Mature leaves densely silky-pubescent; capsule subsessile.
2. Capsule tomentose.
Filaments united; capsule sessile; style none.
Capsule subsessile; style long.
Capsule distinctly pedicelled.
Style filiform, longer than the stigmas.
Leaves white-tomentose beneath.
Leaves silvery-velvety beneath.
Style short, or none.
Leaves finely and sharply serrulate, expanding with the aments.
Capsule short-pedicelled, blunt.
Capsule long-pedicelled, pointed.
Leaves crenate, crenulate or subentire.
Leaves slender-petioled, expanding with the aments.
Leaves short-petioled, expanding after the aments.
Mature leaves glabrous, or somwehat loosely hairy beneath.
Leaves persistently tomentose beneath.
Leaves distinctly petioled; aments 3/4'-1 1/2' long; middle-sized shrub.
Leaves short-petioled; aments 1/2' long; low shrub.
B. Low or depressed, mainly arctic, subarctic and alpine shrubs, mostly less than 30 high (no. 25 sometimes higher; no. 29 extending south to New Jersey and Iowa).
Aments sessile on the branches of the previous year.
Aments on short lateral leafy branches.
Capsule glabrous, or sometimes loosely hairy, not tomentose.
Leaves obovate to oblong.
Leaves nearly orbicular; branches spreading.
Style very short; bracts not herbaceous.
Style long; bracts large, herbaceous.
Capsule tomentose or villous (sometimes glabrous in no. 33).
Style very short or none.
Leaves glabrous beneath when mature.
Leaves permanently silky-hairy.
Capsule distinctly pedicelled.
Mature leaves glabrous or nearly so.
Leaves persistently silvery silky beneath.
Capsule subsessile; leaves entire.
Leaves rounded and obtuse at the apex.
Bracts obovate to oblong, dark brown or blackish.
Bracts oblong, yellow.
Leaves, or some of them, pointed or acute at apex.
Bracts yellow, yellowish or brownish.
Capsules 2"-2 1/2" long; leaves green in drying.
Capsules 3"-4" long; leaves blackening in drying.
Bracts dark brown or blackish.