1 Plants with all leaves alternate.

  2 Bud apex sharp-pointed; bud scale margin free and overlapping; stamens 3-7 (-9); leaf blades 2.5-16× as long as wide; [subgenus Protitea].

    3 Leaf blades (4-) 7-10 (-16)× as long as wide; leaf abaxial surface glaucous (S. caroliniana) or not (S. nigra); floral bracts deciduous after flowering; plants trees [section Humboldtianae].

      4 Plants trees 5-10 m tall; leaves glaucous beneath; pistils borne on stipes averaging 2 mm long (range 1-5 mm); stipules usually prominent and persistent, to 15 mm long; leaf blades (4-) avg. 7.5 (-13)× as long as wide

      4 Plants trees to 20 m tall; leaves not glaucous beneath (or thinly so); pistils borne on stipes averaging 1 mm long (range 0.5-1.5 mm); stipules usually small and caducous, to 12 mm long; leaf blades avg. 9 (-16)× as long as wide

    3 Leaf blades 2.5-5 (-6)× as long as wide; leaf undersurface glaucous; pistillate bracts deciduous (S. amygdaloides) or persistent (S. floridana) after flowering; plants shrubs or trees.

        5 Leaf apex acuminate to caudate; branchlets yellow; pistillate bracts deciduous after flowering; plants trees, usually 4-20 m tall; [NY and PA west to MO, further north and west; primarily midwestern]; [section Humboldtianae]

        5 Leaf apex acute; branchlets reddish brown or green; pistillate bracts persistent after flowering; plants large shrubs or small trees, usually 2-8 m tall; [rare plant of sphagnous seepages in s. AL, s. GA, and FL]; [section Floridanae]

  2 Bud apex blunt or rounded; bud scale margins fused, thus individual scale margins are not distinct or overlapping; stamens usually 2 (except for S. lucida and S. serissima with 3-10 stamens); leaf blades 2-30× as long as wide; plants short to large shrubs, or trees.

          6 Leaves green or pale green beneath, lacking a glaucous bloom.

             7 Leaves linear to lorate (strap-shaped), (7-) 11-35x as long as wide; leaf margins remotely spinulose-serrulate.

               8 Ovaries glabrous or sparsely long-silky; largest medial blades moderately densely hairy or glabrous; staminate abaxial nectaries present; floral bracts sparsely hairy; capsules (4-) 5-8 (-10) mm; [widespread, including s. TX]

               8 Ovaries moderately to very densely short-silky or villous; largest medial blades moderately to very densely appressed hairy; staminate abaxial nectaries absent; floral bracts moderately to very densely hairy; capsules (2.5-) 4-7 mm; [s. TX]

             7 Leaves narrowly oblong to ovate, oblanceolate to lanceolate, broadly to narrowly elliptic, or sometimes lorate; 1.6-6.2 (-8)x as long as wide; if sometimes lorate or narrowly elliptic, then leaf length never exceeding the leaf width by more than 8x; leaf margins primarily serrate, serrulate, or crenulate but not remotely spinulose-serrulate.

                 9 Stipules not glandular on their margins; pistillate floral bracts present after flowering; petioles not glandular; stamens 2; [subgenus Salix, section Salicaster].

                   10 Stipules on early leaves absent or minute; abaxial leaf surface usually ± glabrous, only thinly glaucous, if at all; leaves with white hairs only (when present); leaf apex usually acuminate, sometimes acute (rarely subcaudate); branches dull or slightly glossy; pistillate catkins stout to globose, 11-22 mm wide; stigma lobes 0.4-0.7 mm long; capsules (6-)7-12 mm long; plants fruiting in late summer or in fall; [mostly exclusive to rich fens and other high pH wetlands; PA northward]

                   10 Stipules on early leaves foliaceous; abaxial leaf surface glabrous, pilose, or moderately densely villous to long-silky; leaves (at least juvenile) with a mix of white and ferruginous hairs; leaf apex usually long-acuminate to caudate; branches slightly to highly glossy; pistillate catkins slender to stout, 7-15 mm wide; stigma lobes 0.2-0.4 mm; capsules 5-7 mm long; plants fruiting in late spring or summer [riparian and gravelly floodplain habitats, stream shores, lake margins, occasionally in fens or marly peatlands; VA northward]

                 9 Apex of petiole without glands (petiole sometimes tomentose or pubescent, but lacking glands); leaf apex rounded, blunt, or acute (sometimes acuminate in S. eriocephala); stamens usually 2; [subgenus Vetrix)

                     11 Leaf blades 2.3-8x as long as wide, the margins serrulate or crenulate; the teeth without glands or if present, very small; stipules not glandular on their margins; pistillate floral bracts densely pubescent, present after flowering; branchlets densely to sparsely puberulent, rarely villous; plants flowering just prior to leaf emergence; [widespread in our area]; [section Cordatae]

                     11 Leaves 1.6-3.2x as long as wide, the margins sharply (sometimes doubly) serrate; the teeth with prominent glands; unfolding leaves with long, dense, silky hairs; branchlets ± villous-pubescent; plants flowering just as leaves emerge; [Great Lakes sand dunes and beaches, limited to Presque Isle, PA in our area]; [section Hastatae]

          6 Leaves glaucous or strongly whitened beneath.

                       12 Leaves 10-35 as long as wide; linear or lorate (strap-shaped); margins entire or remotely spinulose-serrulate; [streams, sandbars, and similar gravelly riparian habitats]; [s. TX, westward].

                          13 Abaxial leaf surface silky or pilose; branchlets densely short-silky-tomentose to short-villous; leaf margins usually entire; plants to 17 m tall

                          13 Abaxial surface glabrous, glabrescent, densely villous, or long- or short-silky; branchlets tomentose or pubescent to glabrescent; leaf margins usually spinulose-serrulate; plants to 10 m tall

                       12 Leaves 2-9x as long as wide; narrowly oblong, narrowly elliptic, elliptic, lanceolate, oblanceolate, obovate, or narrowly ovate; if lorate or narrowly elliptic then l:w ratio not exceeding 9x; leaf margins entire, crenate, crenulate, serrulate, serrate, or irregularly toothed; [in a variety of habitats]; [widespread, including TX].

                            14 Leaf margin crenate, crenulate or entire; if teeth present, then these generally rounded; if teeth are somewhat pointed, then these spaced irregularly and often mixed with crenulate teeth on the same plant; [subgenus Vetrix].

                              15 Leaves without revolute margins, flattened or undulate.

                                16 Leaf blades consistently entire, lacking teeth; leaf surface usually glabrous (very rarely sparsely short-silky)

                                16 Leaf blades with some toothing, usually somewhat crenate, not consistently entire; leaf surface usually at least somewhat pubescent.

                                  17 Leaf blades coriaceous and regularly toothed, strongly glaucous abaxially; leaf margins crenulate or serrulate; aments precocious to coetaneous

                                  17 Leaf blades not coriaceous, with fewer teeth, obscurely or prominently glaucous abaxially; leaf margins mostly crenate, sometimes crenulate, entire, or irregularly serrate; aments precocious (sometimes emerging immediately prior to leaves).

                                    18 Upper (adaxial) surface of leaves usually impressed-veiny, pubescent; proximal blade margins gland-dotted; branchlets pubescent; winter buds red to red-brown

                                    18 Upper surface of leaves less noticeably veiny (or at least not conspicuously impressed veiny), tomentose or glabrous; proximal blade margins not gland-dotted; branchlets glabrate or sometimes with small patches of nodal hairs, but not persistently pubescent; winter buds yellow, yellow-brown or red-brown

                              15 Leaves slightly or strongly revolute along the margins.

                                       19 Leaf margin entire and undulate; plants native shrubs, < 2 m tall (occasionally to 3 m tall); floral bracts 0.8-2 mm long; pistillate aments 1-3.5 cm long; pistils borne on stipes mostly < 2 mm long; staminate aments 0.5-2 cm long.

                                         20 Leaf adaxial surface conspicuously veiny-rugose; leaf abaxial surface densely wooly; catkins 17-39 mm long; filaments glabrous; [fens and other alkaline wetlands]

                                         20 Leaf adaxial surface not veiny-rugose (or only weakly so); leaf abaxial surface whitened, but not wooly; catkins 9-47 mm long; floral bracts 1.2-2 mm long; filaments glabrous or basally pubescent; [forest edges, successional habitats, open sandy or rocky habitats and other similar dry to mesic habitats; associated southward with mafic habitats]

                                           21 Leaves stipulate; leaf blades (5-) avg. 7 (-13) cm long, (12-) avg. 17 (-35) mm wide; staminate aments 1-2 cm long; pistillate aments 2-3.5 cm long; [open, upland habitats, shrubby or rocky balds or rocky, open woodlands, powerline clearings, barrens, woodland borders, fens and grassy balds over mafic rocks (e.g. amphibolite) up to at least 1800m elevation]

                                           21 Leaves exstipulate (without stipules); leaf blades (2.5-) avg. 4 (-5) cm long, (5-) avg. 7 (-10) mm wide; staminate aments 0.5-1.1 cm long; pistillate aments 1-2 cm long; [barrens, glades, rocky or hardpan woodlands, prairies, powerline rights-of-way, rarely in depression ponds]

                                       19 Leaf margin crenate to irregularly serrate (rarely nearly entire), if serrate then the teeth irregularly spaced and not sharply pointed; plants non-native, shrubs to small trees, 3-15 m tall; floral bracts 1-4 mm long; pistillate aments 3-8 cm long; pistils borne on stipes mostly > 2 mm long; staminate aments 2-5 cm long.

                                             22 Trees or tall shrubs, to 15 m tall; decorticated wood of 1-4 year old branches smooth or with a few ridges usually < 5 mm long (striae not dense); floral bracts 2-4 mm long

                                             22 Shrubs, 3-7 (12) m tall; decorticated wood of 1-4 year old branches with numerous prominent ridges (dense striae), many of the ridges longer than 2 cm; floral bracts 1-3 mm long

                                               23 Abaxial leaf surface with a mixture of white and rusty (ferrugineous) hairs; branches yellowish to reddish; plants with single stems or trunks 3-12 m tall

                                               23 Abaxial leaf surface with a mixture of white or gray hairs, without ferrugineous hairs; branches grayish; plants multi-stemmed shrubs to 3-7 m tall

                            14 Leaf margins serrate, serrulate, denticulate, or remotely spinulose-serrulate.

                                                 24 Plants shrubs, to 6 m tall; if large shrubs or small trees then the form vase-like, bushy and upright (not weeping or with strongly pendulous branches); plants clonal and growing in dense patches OR as single-stemmed to clumped shrubs; leaves lacking stomates on the upper surface; catkins precocious to coetaneous [native to our area]; [subgenus Vetrix].

                                                    25 Petioles with one pair (or more) of distal spherical glands.

                                                      26 Leaf abaxial surface thinly glaucous; leaf margins consistently serrate, the apices acuminate, caudate or acute; petioles deeply grooved; branches flexible and sometimes brittle; [plants of rich alkaline wetlands]

                                                      26 Leaf abaxial surface thickly or conspicuously glaucous, sometimes densely obscured by short-silky hairs; leaf margins usually a mix of crenate, crenulate, or serrulate teeth, the apices acute, acuminate or convex; petioles convex, flat, or shallowly grooved; branches highly brittle; [sandy or cobbly river and lake shores, swamps, ditches, fens, other various habitats]

                                                        27 Leaves coriaceous, abaxial surfaces thickly glaucous, the margins mostly obscurely crenate to crenulate, sometimes crenulate-serrulate; staminate catkins emerging before leaves, pistillate as leaves emerge; capsules 5-11 mm long, glabrous; filaments glabrous throughout

                                                        27 Leaves not coriaceous, abaxial surfaces glaucous, sometimes obscured by densely short-silky hairs, the margins serrulate or less often obscurely crenulate (proximal blades sometimes nearly entire); catkins flowering as (coetaneous) or just before leaves emerge; capsules 2.5-4 mm long, pubescent; filaments pubescent

                                                    25 Petioles lacking distal glands.

                                                          28 Leaves lorate, narrowly elliptic, or narrowly oblong; abaxial leaf surfaces glaucous and often sparsely to densely silky pubescent; leaf blade bases cuneate; stipules absent to rudimentary (or distally foliaceous on later stipules); capsules silky-pubescent

                                                            29 Leaf blades 2.5-7 cm long, sometimes nearly entire at the base; stipules absent or minute; branches flexible (not breaking cleanly at junction of annual growth); leaf blades (at least expanding leaves) with ferrugineous and white hairs, the abaxial surface sparely to densely pubescent; capsules 5-9 mm long, beaked; [section Geyerianae]

                                                            29 Leaf blades 4-15 cm long, serrulate to the base; stipules absent or of small glands (rarely to 4 mm long on vigorous shoots); branches brittle (breaking cleanly at junction of annual growth); mature leaves short-sericeous abaxially, but lacking red-brown hairs; capsules 2.5-4 mm long, not beaked [section Griseae]

                                                          28 Leaves narrowly elliptic, elliptic, narrowly oblong, obovate or oblanceolate; abaxial leaf surfaces thickly glaucous and glabrous to sparsely pubescent (thus glaucous surface usually very conspicuous); leaf blade bases cordate, rounded, or broadly cuneate; stipules foliaceous or rudimentary to absent; capsules glabrous.

                                                              30 Stipule apices rounded or acute; mature leaves glabrous or glabrescent abaxially; leaf apices usually acute or acuminate (occasionally rounded); leaf margins serrate or serrulate; floral bracts 0.8-1.5 mm long, with wavy pubescence; anthers 0.4-0.64 mm long; styles 0.3-0.6 mm long; [widespread, section Cordatae]

                                                              30 Stipule apices acute or acuminate; mature leaves glabrous or pilose abaxially, usually strongly glaucous; leaf apices usually acute, sometimes rounded or short-acuminate; leaf margins usually crenulate or crenulate-serrulate; floral bracts 1.5-3 mm long (avg. 1.8 mm), with straight hairs; anthers 0.52-0.76 mm long; styles 0.5-1.3 mm long; [PA northward, section Hastatae]

                                                 24 Plants full-sized trees, usually 10-25 m tall on mature individuals; the form or silhouette often appearing weeping on full-sized trees; catkins coetaneous (occasionally precocious in S. babylonica); [non-native in our area, subgenus Salix]

                                                                 31 Leaf margin coarsely and irregularly serrate; leaves glabrous beneath; leaf blade 4-7 (-10)× as long as wide; petioles (7-) 10-20 mm long, glabrous; [section Salix]

                                                                 31 Leaf margin minutely and uniformly serrulate; leaves long-sericeous or glabrate beneath; leaf blade 5-13× as long as wide; petioles 3-12 mm long, tomentose or sericeous.

                                                                   32 Leaves long-sericeous beneath; branches ascending (rarely pendulous); leaves narrowly lanceolate, with length/width ratio of 5-6.5; petioles 3-6 mm long, sericeous, with spherical glands or lobes distally; flowering branchlets 1-1.5 cm long; [section Salix]

                                                                   32 Leaves glabrate beneath; branches normally pendulous; leaves very narrowly lanceolate, with length/width ratio of 6.5-13; petioles 7-12 mm long, tomentose, eglandular or with spherical glands or lobes distally; flowering branchlets ca. 0.3 cm long; [section Subalbae].

                                                                     33 Branches yellowish, yellow-green, or yellow-brown

                                                                     33 Branches yellow-brown to red-brown, or gray-brown.

                                                                       34 Pistillate catkins on branchlets that are (0-) 2-4 mm long; ovary beak abruptly tapered to styles; anthers 0.4-0.5 mm long

                                                                       34 Pistillate catkins on branchlets that are 3-14 mm long; ovary beak gradually tapered to styles; anthers 0.5-0.8 long.

                                                                         35 Petioles glabrous, pilose, or velvety to glabrescent on the upper surface; branches yellow-brown, gray-brown, or red-brown; staminate catkins loosely flowered, stout, nectaries connate and shallowly cup-shaped

                                                                         35 Petioles short-silky on the upper surface; branches yellow-brown; staminate catkins moderately densely flowered. slender, nectaries distinct

1 Leaves evergreen.

  2 Plant a shrub, erect, not requiring support.

    3 Leaves with spiny margins

    3 Leaves with crenate or serrate margins.

      4 Leaves slightly to strongly fleshy; inflorescence a head; [maritime situations]

      4 Leaves not fleshy; inflorescence either a head or otherwise; [collectively widespread].

        5 Leaves > 8 cm long, typically spotted with yellow, coarsely toothed; fruit a red drupe; [commonly cultivated, rarely seeding down nearby]

        5 Leaves < 8 cm long, not yellow-spotted, serrulate; fruit a capsule or purplish drupe; [plants native or cultivated].

          6 Inflorescence a head; [s. FL]

          6 Inflorescence otherwise; [more widespread].

             7 Corolla tubular, campanulate, bilaterally symmetrical; fruit a 1-seeded achene (rarely produced)

             7 Corolla radially symmetrical, with 4-5 distinct petals; fruit a 2-10-seeded capsule or drupe.

               8 Fruit a 4-5-locular capsule, with 2 seeds per locule (though often fewer by abortion)

               8 Fruit a (2-) 3-locular, purplish-black drupe, with (2-) 3 single-seeded stones

  2 Plant a subshrub, creeping shrub, or liana.

                 9 Leaves spinose-serrate; [exotics, rarely naturalized]

                 9 Leaves serrate (not spinose), serrulate, or crenate; [exotics and natives, collectively widespread].

                   10 Leaves slightly to strongly fleshy; inflorescence a head; [maritime situations]

                   10 Leaves not fleshy; inflorescence otherwise; [collectively widespread].

                     11 Leaves on vigorous shoots with a few coarse rounded teeth towards the base (most leaves entire)

                     11 Leaves serrulate to serrate, the teeth uniformly around the margin or concentrated towards the tip; fruit dry, either indehiscent and 1-seeded or capsular and with several seeds.

                       12 Flowers 5-merous; petals fused; fruit indehiscent, 1-seeded; [montane, from e. TN, WV, and w. MD northwards in our area]

                       12 Flowers 4- or 5-merous; petals separate; fruit capsular, dehiscent, several-seeded; [collectively widespread in our area]

1 Leaves deciduous.

                          13 Leaves slightly to strongly fleshy; inflorescence a head, subtended by an involucre of phyllaries; [maritime situations]

                          13 Leaves not fleshy; inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head subtended by bracts, but then with other features differing, such as stamens 4, or green calyx present, or petals separate, or fruit a schizocarp of mericarps, etc.); [collectively widespread].

                            14 Lianas climbing by twining or by adventitious roots.

                              15 Stems with retrorse prickles; foliage scabrous

                              15 Stems not prickly; foliage smooth to variously hairy, but not scabrous.

                                16 Leaves on vigorous shoots with a few coarse rounded teeth towards the base (most leaves entire), the larger leaves < 3 cm wide; lianas climbing by twining; fruit a fleshy berry; flowers 5-merous, with a fused, tubular corolla

                                16 Leaves serrate, the teeth towards the leaf apex, the larger leaves > 4 cm wide; lianas climbing by adventitious roots; fruit a capsule; flowers 7-10-merous, with separate petals

                            14 Upright shrubs or trees, lacking any adaptations for climbing.

                                  17 Trees; leaves often a mix of alternate and opposite.

                                    18 Leaves harshly scabrous on the upper surface; fruit a multiple of achenes; leaf venation pinnate but irregular

                                    18 Leaves not scabrous; fruit a 2-4-seeded drupe; leaf venation neatly pinnate, the lateral veins nearly straight and parallel to one another

                                  17 Shrubs or trees; leaves strictly opposite (or often a mix of alternate and opposite in RHAMNACEAE).

                                       19 Trees; leaves palmately-veined, with 5 or more veins from the base; [rarely naturalizing]

                                       19 Shrubs; leaves either triple-veined from near the base or pinnate-veined; [collectively widespread and common]

                                         20 Leaves strongly triple-veined from at or near the base of the blade, the 2 lateral veins arching towards the tip and rejoining the midvein or nearly so (becoming diffuse before rejoining); petals 4, white; stamens 15-90

                                         20 Leaves pinnate-veined; petals various, not both 4 and white (except sometimes in Hydrangea); stamens 1-15 (except 15-30 in Exochorda in ROSACEAE).

                                           21 Inflorescence head-like; flowers sympetalous and 4-lobed; fruit 2 seeded

                                           21 Inflorescence more diffuse, with internal axes and pedicels; flowers not both sympetalous and 4-lobed (except in Forsythia and Buddleja); fruit 1-seeded, 2-4-seeded, or 4-many-seeded.

                                             22 Plants in flower.

                                               23 Corolla absent; flowers inconspicuous and small, in axillary fascicles or catkins.

                                                 24 Flowers in axillary fascicles; leaves strictly opposite (subopposite)

                                               23 Corolla present; flowers larger, in terminal cymes, corymbs, racemes, panicles, or in axillary cymes or fascicles.

                                                    25 Petals separate; stamens 8-10 (-60) (or 4-6 in RHAMNACEAE and Euonymus in CELASTRACEAE).

                                                      26 Flowers 1-few, in axillary cymes; stamens 4-6; stems brown, tan, gray, or green.

                                                        27 Leaf venation pinnate, but irregular and reticulated; stems green

                                                        27 Leaf venation neatly pinnate, the lateral veins nearly straight and parallel to one another; stems brown, tan, or gray

                                                      26 Flowers 1 and terminal, or many, in terminal panicles or corymbs; stamens 8-10 (-60); stems brown, tan or gray.

                                                          28 Inflorescence a solitary, terminal flower; stamens 30-60

                                                          28 Inflorescence a terminal panicle or corymb; stamens 8-15

                                                    25 Petals fused, at least basally, and often strongly tubular; stamens 2, 4, or 5.

                                                            29 Stamens 5.

                                                              30 Petals white, fused basally only, the lobes spreading

                                                              30 Petals pink, yellow, or reddish, fused for most of their length

                                                            29 Stamens 2 or 4.

                                                                 31 Stamens 2; petals yellow; flowers radially symmetrical; inflorescence an axillary fascicle

                                                                 31 Stamens 4; petals white, pink, or lavender; flowers bilabiate; inflorescence a terminal thyrse or panicle or an axillary cyme.

                                                                   32 Petals 4; inflorescence a terminal thyrse

                                                                   32 Petals 5; inflorescence a terminal panicle or an axillary cyme.

                                                                     33 Inflorescence an axillary cyme

                                                                     33 Inflorescence a terminal panicle

                                             22 Plants in fruit.

                                                                       34 Fruit a berry, drupe, or achene, indehiscent, fleshy at maturity (or dry in Kolkwitzia).

                                                                         35 Fruit a berry, with 20+ seeds

                                                                         35 Fruit a drupe or achene, with 1-4 seeds.

                                                                           36 Fruit an achene (1-seeded), dry at maturity

                                                                           36 Fruit a drupe (1-4-seeded), fleshy at maturity.

                                                                              37 Inflorescence a terminal corymb

                                                                              37 Inflorescence axillary, fascicled or a cyme.

                                                                                38 Foliage with stellate hairs; fruit a pink-purple 4-seeded drupe

                                                                                38 Foliage glabrous or with simple hairs; fruit a dark red, black, or blue 1-4-seeded drupe.

                                                                                  39 Fruit a 1-seeded drupe; [NC southwards and westwards]

                                                                                  39 Fruit a 2-4-seeded drupe; [widespread in our region]

                                                                       34 Fruit a capsule, dehiscent, dry at maturity.

                                                                                    40 Inflorescence a catkin, the flowers small (< 5 mm in diameter) and tightly arranged on the inflorescence axis (> 5 per cm of the axis)

                                                                                    40 Inflorescence various, but more diffuse, the flowers larger (> 5 mm in diameter, except for some flowers in Hydrangea in HYDRANGEACEAE) and loosely arranged (< 5 per cm of axis).

                                                                                      41 Capsule prominently 5-angled (star-shaped in ×-section)

                                                                                      41 Capsule not angled.

                                                                                        42 Inflorescence axillary, fascicled.

                                                                                           43 Capsule pink to red; fruits solitary or in axillary cymes

                                                                                           43 Capsule brown; fruits in axillary fascicles

                                                                                        42 Inflorescence terminal, a raceme, panicle, corymb, or compound cyme or thyrse.

                                                                                             44 Inflorescence a flat-topped corymb or rounded compound cyme, as wide as or wider than long

                                                                                             44 Inflorescence elongated, a raceme, panicle, or thyrse, much longer than wide.

                                                                                               45 Capsule elongate (> 3× as long as wide), 8-25 mm long

                                                                                               45 Capsule about as long as wide, 3-6 mm long.

                                                                                                 46 Sepal lobes 5

                                                                                                 46 Sepal lobes 4