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Salix

The flower of a willow consists of a single pistil or (1–) 2–7 (occasionally more) stamens apparently in the axil of a small scale or bract. These flowers are grouped in “catkins” or aments. Since the flowers are small and lack a perianth, the species are more difficult to describe than in many genera, with the added complications that the sexes are on separate plants and that in many species the flowers appear before the leaves. In addition, hybridization is not uncommon among certain species, so that the willows have a reputation for being unusually difficult to identify.

The general key below includes all species, and is based on characteristics of the flowers, fruit, and leaves. It includes fairly full descriptions of the species insofar as they differ from each other, and is intended to work with either staminate or pistillate plants, as long as leaves are present. In addition, supplementary keys are provided for staminate and pistillate plants of those species that may be found (at least sometimes) with the flowers or fruit well developed before the leaves appear. These keys will be helpful in many cases, but additional leaf collections from the same individual plant should be made for certainty.

Identification of willows requires patience and good magnification of about 10× with adequate illumination. In several species, the presence or absence of copper-colored hairs on young foliage is a very helpful characteristic; do not assume that these are absent until a careful search has been made. Similarly, examine the petioles of a number of leaves before concluding that glands are absent. Look at several leaves to gain an impression of shape and the nature of the margin. In short, do not base decisions on a single examination of a single part. In a few species, the sequence of flowering in the ament is distinctive. This is a characteristic best seen in partly developed staminate aments; fully mature or exceedingly young aments will not demonstrate the sequence. The filaments of older stamens may shrivel and shorten, making them falsely appear younger, so great caution must be exercised in using this character. In S. discolor, S. humilis, S. myricoides, and S. cordata the first well-developed stamens with mature anthers appear at the apex of the ament, those at the base developing subsequently.

Salix babylonica L., Weeping Willow, has been reported from the state, but is barely hardy quite this far north. True S. babylonica has capsules shorter than either S. alba or S. euxina, and the leaves are finely toothed. Most if not all Weeping Willows in this region are actually more hardy hybrids of S. babylonica with S. euxina (S. ×pendulina Wenderoth) and S. alba (S. ×sepulcralis Simonk.), if not simply cultivars of S. alba var. tristis. We have few documented records of any Weeping Willow (i.e., one with long pendulous branches) escaping from cultivation in Michigan, though they may persist long after cultivation, but we have seen a very few collections of both S. ×pendulina and S. ×sepulcralis apparently growing outside of cultivation.

GENERAL KEY

1. Leaves green beneath (similar to upper surface, or ± yellow-green, glabrous or pubescent, but neither whitened nor glaucous nor with the surface hidden by dense white pubescence).

2. Leaves ± entire, revolute, the upper surface with impressed (sunken) veins; capsules (and often other parts) white-tomentose; stamens 2, the filaments glabrous.

S. candida (in part)

2. Leaves serrate to remotely denticulate (very young ones sometimes nearly entire), not revolute (though margins sometimes thickened), the upper surface smooth or with the veins slightly raised; capsules and young growth glabrous to silky, but not tomentose; stamens various.

3. Leaf blades remotely denticulate (the greatest distance between teeth on mature leaves mostly 3–6 mm), mostly linear-oblong or narrowly lanceolate; stipules minute or none; stamens 2, the filaments densely pilose on lower half; capsules pubescent or glabrous.

S. exigua (in part)

3. Leaf blades closely serrate (the teeth on mature leaves usually much less than 3 mm apart), narrowly lanceolate to ovate or elliptic (except in S. nigra, with 4–7 stamens); stipules, at least on shoots, conspicuous in some species; stamens more than 2 or the filaments nearly or quite glabrous; capsules glabrous.

4. Blades linear-lanceolate, acute to somewhat rounded at base, at maturity mostly 4–10 times as long as wide; stamens 4–7; petioles usually not glandular at the summit; capsules 3–4 (–4.8) mm long, with styles less than 0.3 mm long (or rarely slightly longer).

S. nigra

4. Blades lanceolate or broader, rounded to subcordate at base, at maturity 1.5–6 times as long as wide; stamens 2 or if more the petioles glandular at the summit; capsules various.

5. Petioles with 2 or more glands at or near junction with the blade; stamens (2–) 3 or more (usually 5); year-old branchlets glabrous and usually shiny.

go to couplet 22

5. Petioles without glands (though margin of blade may be glandular-toothed nearly to its base); stamens 2; year-old branchlets often pubescent or at least puberulent above the nodes.

6. Unfolding leaves, even if (as occasionally) reddish, mostly covered with dense long silky hairs; older leaves densely hairy to glabrate, definitely green beneath (at least under the hairs), the margins usually sharply (sometimes doubly) serrate, the teeth tipped with prominent enlarged glands; stalks of the ovaries under 1 mm long, shorter than the scales; styles usually 0.6–1.5 mm long; young staminate aments flowering from apex to base; branchlets ± villous-pubescent.

S. cordata (in part)

6. Unfolding young leaves usually very reddish, moderately to very sparsely pubescent; older leaves usually somewhat whitened beneath, glabrous or nearly so, the marginal teeth tending to be crenulate and with glands absent or very small and ± sunken; stalks 1–2.5 mm long, usually about equaling or exceeding the scales; styles ca. 0.5 mm long or shorter; young aments flowering from base to apex; year-old branchlets densely to sparsely (and in patches) puberulent, rarely somewhat villous.

S. eriocephala (in part)

1. Leaves whitened beneath, usually ± strongly glaucous and/or the lower surface completely hidden by dense white pubescence.

7. Margins of foliage leaves (not always peduncular bracts) entire or sometimes (especially on sprouts) rather coarsely and irregularly or obscurely crenulate-serrate on apical half, often ± revolute; stamens 2 (or 1 in S. purpurea); capsules pubescent (except in S. pedicellaris and S. myricoides) [Note: All species included under this lead, except S. pedicellaris, are also in the supplementary keys to flowering specimens; those keys may be helpful to consult for material with aments but with leaves not yet fully mature].

8. Leaves completely glabrous (or hairy when first emerging from bud, the hairs rapidly deciduous).

9. Aments on long or short branchlets (“peduncles”) bearing green bracts or leaves; capsules glabrous, on stalks 1.2–4 mm long; filaments glabrous; anthers yellow; axillary buds at most 5 mm long (S. pedicellaris) or 7 mm (S. myricoides), leaves strictly entire or obscurely toothed.

10. Aments up to 3 cm long, terminating leafy branchlets ca. 1–3 cm long; capsules strongly red tinged (rarely bright green); style very short, not over 0.3 mm long; anthers ca. 0.5 (0.4–0.6) mm long; leaves strictly entire, slightly revolute, often ± rounded at apex; branchlets glabrous; stipules absent.

S. pedicellaris

10. Aments at maturity 3–9 cm long (or the staminate, and rarely pistillate, as short as 2 cm), on short green-bracted branchlets; capsules yellow-brown to greenish; styles usually 0.6–1.5 mm long; anthers 0.6–1 mm long; leaves ± acute at apex, with at least a few obscure teeth; branchlets, especially of current year, usually ± densely pubescent; stipules often present.

S. myricoides (in part)

9. Aments essentially sessile, at most with tiny green or brown bracts at base; capsules pubescent, the stalks various; filaments often pilose at base; anthers yellow to red or purplish; axillary buds up to 13 mm long on sprouts (though often under 5 mm, especially in S. discolor and S. planifolia); leaves ± obscurely toothed on about the apical third or half.

11. Capsules less than 3 mm long, sessile; styles essentially none; filaments (and sometimes anthers) united into a single stamen pilose at the base; anthers less than 0.5 mm long, dark brown or purplish; stipules none; leaves often tending to be subopposite (especially on older twigs), thickish, purplish, ± oblanceolate or narrowly oblong; shrub escaped from cultivation.

S. purpurea

11. Capsules (3.5–) 5–10 mm long, sessile or on stalks up to 4.5 mm long; styles usually 0.5–1 mm or (in S. planifolia) longer; filaments distinct, glabrous or pilose at the base; anthers ca. (0.5–) 0.6–1.2 mm long, yellow or sometimes flushed with reddish; stipules often present; leaves alternate, thin, the blades green (above), obovate (-oblanceolate) to elliptic; shrubs native.

go to couplet 18

8. Leaves pubescent on one or both surfaces, at least until well opened.

12. Branchlets glabrous, usually ± strongly and extensively glaucous; leaf blades rather densely covered with lustrous hairs beneath when mature (glabrous or nearly so above), with narrowly but strongly revolute margins; stipules none.

S. pellita

12. Branchlets pubescent or glabrous, not (or occasionally slightly) glaucous; leaves and stipules various.

13. Pubescence of leaves consisting of straightish, silky, and appressed hairs.

14. Leaf margins ± revolute; capsules sessile or nearly so; styles 0.5–1.5 mm long; plant escaped from cultivation.

S. viminalis

14. Leaf margins at most thickened, not revolute; capsules distinctly stalked (stalks 0.5–3.5 mm long); styles less than 0.5 mm long; plants widespread native shrubs.

go to couplet 33

13. Pubescence of leaves consisting of ± curled, tomentose, or woolly hairs (at most silky on youngest leaves just emerging from bud).

15. Under surface of leaf blade actually green, hidden by dense white- or gray-tomentose pubescence (rarely glaucous with sparser white tomentum); blades linear to lanceolate or narrowly oblong, (4–) 5–12 (–17) times as long as wide; ovary and capsule ± densely white-tomentose, on a stalk up to 1 mm long; young branchlets usually with flocculent tomentum.

S. candida (in part)

15. Under surface of blades ± whitened or glaucous, seldom completely hidden by the pubescence; blades generally broader, usually less than 5 times as long as wide (rarely up to 6 times); ovary and capsule silky-pubescent, on a stalk 1–6 mm long; young branchlets glabrous or puberulent to villous (not flocculent-tomentose).

16. Aments on short leafy branchlets; pubescence (even on young reddish leaves) whitish, without admixture of red or coppery hairs; leaves usually retaining at least sparse pubescence throughout above when fully developed, rugose, with veins and veinlets impressed above and prominent beneath; scales of aments rather narrow, whitish to pale brown, of uniform color or slightly darker at base or pink-tipped.

S. bebbiana

16. Aments on short branchlets or sessile, but only rarely leafy-bracted (hybrids?); pubescence of unfolding leaves (especially above) in small or large part of copper-colored hairs; leaves becoming glabrous above when fully developed, except often for whitish or coppery hairs on midrib, flat or (S. humilis) slightly rugose (a few coppery hairs occasionally present at maturity); scales of aments typically rather broad, ± obovate, very dark brown to black except for pale base.

17. Year-old branchlets glabrous.

18. Capsules ca. (3.5–) 4–6 mm long, sessile or on stalks up to 1 mm; styles 0.7–1.5 mm long; leaf blades glossy (rarely dull) dark green above with ± parallel lateral veins; Isle Royale.

S. planifolia

18. Capsules (5–) 6–10 mm long, on stalks (1–) 1.5–4.5 mm; styles usually 0.5–1 mm long; leaf blades not glossy, with more irregular lateral veins; common throughout Michigan.

S. discolor (in part)

17. Year-old branchlets pubescent or puberulent at least in small patches above the nodes [Note: Vegetative specimens not safely distinguished; see text. If old aments are present, the following may help].

19. Pistillate aments 0.5–2.5 (rarely to 4 or even 5.5) cm long; anthers red-purple to brown, 0.4–0.6 mm long (rarely larger); leaves often slightly rugose (and somewhat revolute-margined), the veinlets impressed above.

S. humilis

19. Pistillate aments 3–12 (–14) cm long; anthers yellow or flushed with reddish, (0.6–) 0.7–0.9 (–1.2) mm long; leaves flat or the main veins slightly raised above.

20. Wood smooth beneath the bark; common native shrub.

S. discolor (in part)

20. Wood (at least of 2–3-year-old twigs) with distinct long ridges beneath the bark; rare escape from cultivation.

21. Leaves with only white or light gray hairs on the underside.

S. cinerea

21. Leaves with whitish plus at least some rusty hairs on the undersurface.

S. atrocinerea

7. Margins of leaves (at least mature foliage leaves) ± finely and distinctly serrate (the teeth rather distant in S. exigua and S. euxina) almost or quite to the base of the blade; stamens 2 to several; capsule pubescent or glabrous.

22. Petiole with prominent (sometimes stalked) glands or projections above, at, or near junction with the blade.

23. Leaves lanceolate to linear-lanceolate, attenuate to apex; capsules 3–6 mm long; stamens 2–3.

24. Blades of leaves usually ± silky, at least beneath, at maturity, with 6–10 (–13) teeth per cm on the margin; capsules 3–3.5 (–4.5) mm long, sessile or nearly so.

S. alba (in part)

24. Blades of leaves glabrous at maturity (silky when very young), with 4–6 teeth per cm on the margin; capsules 3.5–6 mm long, on short stalks ca. 0.7 mm long.

S. euxina (in part)

23. Leaves broadly lanceolate to ovate-elliptic with acute or acuminate apex; capsules 4–10 (–12) mm long; stamens usually 5.

25. Blades of mature leaves ca. 1.5–3.5 times as long as wide, green or slightly whitened beneath, acute to short-acuminate; petioles and young foliage glabrous; stipules usually present (falling early) on young sprouts; leaves or leafy bracts on the short flowering branchlets usually entire or nearly so; scales, especially in staminate aments, sparsely pubescent to glabrous except at base; capsules smoothish and 4–6 mm long; uncommon introduced large shrub or small tree.

S. pentandra

25. Blades of mature leaves 2–6 times as long as wide, green to strongly glaucous beneath; leafy bracts of flowering branchlets finely toothed, like the foliage leaves; plants common native shrubs of ± natural habitats. [The two following species differing from S. pentandra as described below; e.g., if leaves whitened beneath, then stipules always lacking, capsules larger, and scales pubescent to their tips; if green beneath, then tending to be long-acuminate on sprouts, often pubescent on petioles when young, the capsules ripening early].

26. Leaves dark to pale green but not whitened beneath,  long-acuminate at maturity often stipulate on sprouts; petioles and young leaves often sparsely to ± heavily pubescent with copper-colored (sometimes whitish) hairs; scales usually with a prominent glabrate area on apical third or half; mature capsules 4–6.5 (–7.5) mm long, smooth (except usually in wrinkled beak), dehiscing before June 15 (or as late as July 1 in northern Michigan or late seasons).

 

S. lucida

26. Leaves somewhat whitened to strongly glaucous beneath, acute or short-acuminate, estipulate; petioles and young leaves glabrous; scales of both staminate and pistillate aments usually ± pubescent to their tips; mature capsules (6–) 7.5–10 (–12) mm long, ± granular-roughened or wrinkled throughout, dehiscing after July 1 (occasionally June 15–July 1 in southern Michigan or in dry or early seasons).

S. serissima

22. Petioles without glands (or these occasionally obscure in S. amygdaloides).

27. Scales of aments yellowish, pilose at base and margins, glabrate on back, deciduous before ripening of capsules; flowers tending to be spaced in whorls, in rather slender, lax aments; capsules glabrous; stamens 2–7; plants native or introduced trees (when full-grown), with lanceolate, usually attenuate leaves, these glabrous to somewhat silky at maturity.

28. Leaves with veinlets coarse or obscure, not forming tiny islets; stamens 2 (–3); capsules 3–6 mm long, sessile or on very short stalks.

29. Blades of leaves usually ± silky, at least beneath, at maturity, with 6–10 (–13) teeth per cm on the margin; capsules sessile or nearly so, 3–3.5 (–4.5) mm long.

S. alba (in part)

29. Blades of leaves glabrous at maturity (silky when very young), with 4–6 teeth per cm on the margin; capsules on short stalks (ca. 0.7 mm long), 3.5–6 mm long.

30. Petioles of larger leaves 8–17 mm long; fully grown leaves 12–30 mm wide; catkins ca. 2–6.5 cm long; branches straight.

S. euxina (in part)

30. Petioles of larger leaves mostly 5–8 mm long; leaves 4–10 mm wide; catkins ca. 1–2.5 cm long; branches contorted.

S. matsudana

28. Leaves with a very fine network of veins, forming tiny islets (ca. 4 per mm) clearly visible below; stamens 4–7; capsules 4.5–6 mm long, on stalks (0.8–) 1–2.5 mm long.

S. amygdaloides

27. Scales (except in the otherwise distinctive S. exigua and S. myricoides) brown to black (pale at base), frequently pilose throughout, persistent; flowers generally crowded into thickish aments; capsules glabrous or pubescent; stamens 2; plants native shrubs, with leaves various.

31. Surface of leaves actually green beneath, covered with dense whitish pubescence.

32. Margins of leaves closely serrate, the teeth tipped with enlarged glands; capsules glabrous; filaments glabrous or nearly so; young aments appearing with or slightly before the leaves; scales dark-tipped, persistent.

S. cordata (in part)

32. Margins of leaves rather remotely denticulate, the teeth often 3 mm or more apart, without enlarged glands; capsules often thinly silky; filaments ± densely pilose on basal half; aments developing after the leaves; scales yellowish, deciduous.

S. exigua (in part)

31. Surface of leaves whitened or glaucous beneath, glabrous or retaining pubescence. [Note: If leaves are rather coarsely crenate-toothed and the specimen does not work well here, try couplet 16. Furthermore, all five species below are included in the supplementary keys to flowering material (although only the last two normally have aments before the leaves); those keys may be helpful to consult for material with aments].

33. Leaf blades ± rounded (occasionally acute) to cordate at base, often over 1.5 cm wide at maturity, glabrous or retaining a little pubescence along the midrib; capsules glabrous; stipules often present and conspicuous, especially on sprouts, ovate to reniform; young unfolding leaves at tips of branchlets usually reddish.

34. Foliage with a definite “balsamic” (almost cosmetic or spicy) odor, which is usually persistent long after drying; mature leaves completely glabrous; year-old branchlets red and shiny, smooth and glabrous (the current year’s branchlets glabrous to somewhat puberulent when very young); mature capsules on stalks 2–4 mm long, subtended by rather uniformly light brown scales.

S. pyrifolia

34. Foliage without balsamic odor; mature leaves often ± pubescent on petioles and midribs; year-old branchlets usually puberulent above the nodes if not more densely pubescent (current year’s branchlets frequently densely short-villous), not shiny and seldom red; mature capsules on stalks 1–3 (–3.5) mm long, subtended by dark brown to black scales pale at the base.

35. Young unfolding leaves ± strongly red, but only with whitish hairs (neither glabrous nor with coppery hairs); mature leaves thinner in texture, ± whitened to almost green beneath, not strongly glaucous; styles ca. 0.5 mm long; young staminate aments flowering from base to apex.

S. eriocephala (in part)

35. Young unfolding leaf blades at tips of branchlets often reddish, glabrous or usually with some copper-colored hairs mixed with whitish; mature leaves thick, usually very glaucous beneath; styles ca. 0.6–1.5 mm long; young staminate aments flowering from apex to base.

S. myricoides (in part)

33. Leaf blades acute to (rarely) rounded at base, nearly always less than 1.5 (rarely to 2) cm wide at maturity, glabrous to silky; capsules at least thinly pubescent; stipules rarely present (at most tiny and narrow); young unfolding leaves not really red, though often with coppery hairs and/or blackening in drying.

36. Mature leaves ± pubescent above or essentially glabrous on both sides, the lateral veins not prominent below; young leaves nearly always with few to many coppery hairs mixed with whitish ones (or practically glabrous); year-old branchlets glabrous (sometimes slightly glaucous) to occasionally slightly puberulent; current year's branchlets puberulent to glabrate; capsules 4.5–8.5 mm long, ± lanceolate.

S. petiolaris

36. Mature leaves glabrous or nearly so above (except for puberulent midrib), the underside ± silky, usually rather densely so, with the main lateral veins prominently rib-like; young leaves densely silky, without any coppery hairs; year-old branchlets puberulent (or sometimes glabrate), those of the current year usually densely so; capsules (2–) 3.5–6.5 mm long, rather plump (ovoid) and rounded at tip.

S. sericea

Supplementary Keys

Do not try to use these keys on specimens either with very immature aments or with foliage leaves developed, as the species may not be included or the measurements may differ from those given here. (Developing leafy bracts may, however, occur on the flowering branchlets or “peduncles” in several species keyed below.)

These keys are only guides to typical material; extremes of variation may cause difficulty. It is always best to collect leaves from the same plant later in the season. Be sure to measure the most mature examples of any part described, and several of them. Stalks of the ovaries, in particular, may be shorter than the measurements given if the flowers are not fully developed. Measurements of styles are of the undivided portion. Measurements are based primarily on dry specimens, and anthers, in particular, may be slightly larger when fresh.

Key to Pistillate Specimens

1. Ovaries completely glabrous.

2. Year-old branchlets (but not necessarily new branchlets) completely glabrous, reddish, shining; bracts on flowering branchlets with conspicuous glandular margins; plants with a balsamic odor persisting in dry specimens; styles scarcely 0.5 mm long.

S. pyrifolia

2. Year-old branchlets ± densely puberulent or pubescent, at least in a small region above each node, scarcely ever both reddish and shining throughout (if smooth, the bracts not conspicuously glandular); flowers sweet-smelling, perhaps, but plants without persistent balsamic odor; styles ca. 0.5–1.5 mm long.

3. Longest styles ca. 0.5 mm long; stalks 1–1.5 (rarely 2.5) mm long, at most equaling to slightly exceeding the body (not hairs) of the subtending scales.

S. eriocephala

3. Longest styles (0.5–) 0.7–1.5 mm long; stalks various.

4. Stalks very short, inconspicuous, scarcely 0.5 mm long (rarely to 1 mm), shorter than subtending scales.

S. cordata

4. Stalks 1–3 mm long, about equaling or exceeding the scales.

S. myricoides

1. Ovaries pubescent.

5. Ovaries sessile or nearly so, even the most mature stalks not exceeding 1 mm, shorter than subtending scales (except often in S. candida).

6. Styles essentially absent, or very short (to 0.4 mm).

7. Ovaries up to 3 mm long; leaves (leaf scars) tending to be subopposite (especially on older twigs); growth of current year not at all begun or essentially glabrous.

S. purpurea

7. Ovaries up to 5.5 mm long; leaves always alternate; youngest branchlets and growth of current year (including bracts on flowering branchlets) just beginning at flowering time, finely silky-pubescent.

S. sericea (in part, but cf. also couplet 15)

6. Styles distinct, 0.5–1.5 (–2) mm long.

8. Pubescence of ovaries (and, usually, bud scales and young branchlets) definitely tomentose or woolly.

S. candida

8. Pubescence silky or velvety, of ± straight hairs.

9. Branchlets puberulent; plant escaped from cultivation.

S. viminalis

9. Branchlets glabrous; native in northern Michigan.

10. Scales brown; branchlets often very glaucous; aments usually appearing as leaves begin to expand.

S. pellita

10. Scales black; branchlets not glaucous; aments appearing strictly before the leaves.

S. planifolia

5. Ovaries on stalks 1–5 mm long (except in very immature aments), in some plants exceeding the subtending scales.

11. Styles 0.5–1 mm long.

12. Wood (at least of 2–3-year-old twigs) with distinct long ridges beneath the bark; rare escape from cultivation.

13. Leaves with only white or light gray hair on the underside.

S. cinerea

13. Leaves with both whitish and rusty hair on the undersurface.

S. atrocinerea

12. Wood smooth beneath the bark; common native shrub.

S. discolor (in part)

11. Styles essentially absent to 0.5 mm long.

14. Scales subtending stalks straw-colored to pale brown, ± elongate, uniformly colored or pinkish at apex or slightly darker at base; stigmas often completely sessile; leafy bracts developing on flowering branchlets; aments 1–6 cm long; year-old branchlets usually pubescent (at least finely puberulent), sometimes glabrous.

S. bebbiana

14. Scales pale to dark brown or black, usually rather broadly elliptic or obovate and paler at base; stigmas usually on short styles; bracts, aments, and branchlets various.

15. Leafy green bracts usually developing on flowering branchlets; aments 1–3 (–3.5) cm long [Note: Mature leaves generally necessary for accurate identification].

16. Year-old branchlets nearly always glabrous and shining, frequently a little glaucous; ovaries usually 2.5–7 mm long, lanceolate (the sides straight to concave, ± tapered to apex).

S. petiolaris

16. Year-old branchlets generally finely puberulent, at least in patches (sometimes completely glabrous); ovaries tending to be shorter (often under 3 mm), blunt, and ovoid (convex-sided).

S. sericea (in part, and some pubescent specimens of S. petiolaris)

15. Leafy bracts not developing on flowering branchlets (at least not until foliage leaves are also present; rarely [hybrids?] earlier); aments 0.5–12 (–14) cm long.

17. Year-old branchlets glabrous.

S. discolor (in part)

17. Year-old branchlets pubescent, at least in patches above the nodes.

18. Aments 3–12 (–14) cm long; mature stigmas often elongate (up to 5–8 times as long as thick and 1 mm long).

S. discolor (in part)

18. Aments 0.5–2.5 (rarely to 4) cm long; stigmas shorter and relatively stouter.

S. humilis

Key to Staminate Specimens

1. Filaments (and sometimes anthers) united, forming a single stamen pilose at the base; leaves (leaf scars) tending to be subopposite (especially on older twigs).

S. purpurea

1. Filaments 2, distinct (or rarely fused at base only), pilose or glabrous; leaves alternate.

2. Flowering branchlets developing at most small brown bracts (occasionally green in S. discolor).

3. Anthers 0.6–1.2 mm long, averaging 0.7–0.8 mm or more; year-old branchlets often (not always) completely glabrous.

4. Wood (at least of 2–3-year-old twigs) with distinct long (several cm) ridges beneath the bark; rare escape from cultivation.

5. Leaves with only white or light gray hair on the underside.

S. cinerea

5. Leaves with both whitish and rusty hair on the undersurface.

S. atrocinerea

4. Wood smooth beneath the bark; common native shrub.

S. discolor

3. Anthers 0.3–0.7 mm long, averaging at most 0.6 mm (usually ca. 0.4–0.6 mm); year-old branchlets densely pubescent throughout to puberulent above the nodes only (or occasionally in yellow-anthered plants completely glabrous).

6. Anthers predominantly yellow (rarely yellow-brown).

go to couplet 8

6. Anthers very dark, red-violet (or pale brown in age, but scales often strongly tinged with red-violet, placing such plants here).

7. Pubescence of branchlets largely or entirely flocculent-tomentose, white; pubescence of scales often ± wavy or curled.

S. candida (in part)

7. Pubescence gray or sordid, villous to puberulent; hairs of scales ± straight.

S. humilis

2. Flowering branchlets developing small to conspicuous leafy green (sometimes densely silky) bracts.

8. Anthers dark red-violet, 0.3–0.5 mm long; pubescence of branchlets, bracts, etc., mostly or entirely flocculent-tomentose, white.

S. candida (in part)

8. Anthers predominantly yellow (to yellow-brown), 0.4–1.1 mm long; pubescence of branchlets not flocculent-tomentose, usually rather gray or sordid, villous to puberulent, or none.

9. Anthers 0.6–1.1 mm long, averaging ca. 0.7 mm or more.

10. Mature scales whitish to pale brown, of uniform color or slightly darker at base or pink-tipped; year-old branchlets pubescent to glabrate.

S. bebbiana

10. Mature scales brown to black, usually paler at base (occasionally ± uniform medium brown or reddish); year-old branchlets pubescent or glabrous.

11. Year-old branchlets completely glabrous.

go to couplet 16

11. Year-old branchlets densely pubescent to finely puberulent, at least in patches above the nodes.

12. Bracts of flowering branchlets densely silky-pubescent beneath, the margins with prominent enlarged ± spherical glands (sometimes hidden in the hairs); aments flowering from apex to base.

S. cordata

12. Bracts thinly silky or glabrous except at base, the margins with glands absent or scarcely enlarged and appearing merely as tips of low teeth; aments flowering variously.

13. Filaments pilose toward base; bracts rather small and inconspicuous.

S. petiolaris (in part)

13. Filaments glabrous; bracts small or, often, well developed and conspicuous.

14. Scales with rather wavy or curled hairs; bracts of flowering branchlets not glandular-margined; aments flowering from base to apex.

S. eriocephala

14. Scales with ± straight hairs; bracts often with small glandular-tipped teeth; aments flowering from apex to base.

S. myricoides (in part)

9. Anthers 0.4–0.7 mm long, averaging at most 0.5–0.6 mm.

15. Year-old branchlets densely pubescent throughout to puberulent at least in small patches above the nodes.

16. Bracts densely silky-pubescent beneath, the margins with prominent enlarged ± spherical glands (sometimes hidden by the hairs); aments flowering from apex to base.

S. cordata

16. Bracts thinly silky or glabrous except at base, the margins without glands; aments flowering from base to apex or from middle to both ends. [The rare escape Salix viminalis will run here, as well as some puberulent-branched specimens of S. petiolaris and small-anthered specimens of S. eriocephala. Pistillate material and/or leaves are necessary to distinguish these with certainty.]

S. sericea (in part)

15. Year-old branchlets completely glabrous.

17. Branchlets rather strongly glaucous.

S. pellita

17. Branchlets not glaucous (or slightly so in S. petiolaris).

18. Branchlets reddish and shiny; margins of bracts prominently glandular-toothed; aments flowering from base to apex; plants with persistent balsamic odor when dry.

S. pyrifolia

18. Branchlets greenish, yellowish, or dark, but seldom red and shiny (cf. S. planifolia); margins of bracts (if any) not glandular, or if obscurely so, the aments flowering from apex to base; flowers sweet-smelling at most, but plant without persistent balsamic odor.

19. Anthers 0.6–1 mm long; aments flowering from apex to base.

S. myricoides (in part)

19. Anthers 0.4–0.7 mm long; aments flowering from base to apex or from middle toward both ends.

20. Scales black; aments sessile, without bracts on flowering branchlets, appearing strictly before the leaves; Isle Royale.

S. planifolia

20. Scales brown; aments usually on bracted flowering branchlets and appearing as leaves begin to expand; widespread.

S. petiolaris (in part, and some specimens of S. sericea, which usually has puberulent branchlets)