Salix L.

1. Salix L. View in CoL 2

Buds with one outer scale. Leaves variously shaped. Flowers entomophilous, appearing before or after the leaves, in catkins, each flower with one or two small nectaries and subtended by an entire bract. Stamens usually 2, 3 or 5. Capsule 2-valved. Seeds numerous.

Although sections have been described in this genus they will not be indicated in the text, since most of them are represented only by a single species or species-group in Europe (with the exception of Sect. Capreae , species 35-43).

Hybridization plays a very important role in Salix . Most hybrids are highly fertile, and in some regions hybrid-swarms obscuring the limits of the species occur. Complex hybrids are also known. On the other hand certain taxa of evidently hybrid but uncertain origin are fairly well stabilized. These have not been included in the key but are mentioned after the species to which they show most resemblance. It is not possible to provide a separate key for non-flowering plants as there is too much parallel variation in most species in indumentum, leaf-shape, and leaf-margin, etc.

The key is therefore based on the rather unrealistic assumption that the plant to be named is represented by branches bearing male catkins, female catkins, and leaves, and that notes on its habit and habitat are also available.

The following hints may prove useful, however, when attempting to identify incomplete specimens:

1. Plant procumbent, withstemappressed to the ground: 6. reticulata , 9-11. retusa group, 12. rotundifolia , (13-15). myrsinites group in part, 16. arctica , 21. pyrenaica , 22. reptans .

2. Stems underground: (a) mountains and arctic: 7. herbacea , 8. polaris ; (Z?) bogs, swamps or on sand: 48. myrtilloides , (49-51). repens group.

3. Branches with a bluish, waxy bloom: 69. daphnoides , 70. acutifolia .

4. Decorticated twigs with prominent ridges: 26. bicolor , 36. aegyptiaca , (37. appendiculata ), 39. cinerea , 41. aurita , (45. cantabrica ), 40. atrocinerea .

5. Leaves narrowly linear and more or less entire: (50. rosmarinifolia ), (60-61). viminalis group, 62. elaeaegnos, (65. caspica ), 66. wilhelmsiana.

6. Leaves very glossy above: 1. pentandra , 32. glabra .

7. Leaves regularly blackening on drying: 29. nigricans , 32. glabra , 63. purpurea

8. Leaves glabrous even when young: 1. pentandra , 2. fragilis , 5. triandra , 32. glabra , 63. purpurea , 67. caesia .

9. Leaves with appressed silky indumentum: 3. alba , (18-20). glauca group, 45. cantabrica , (49-51). repens group, (60-61). viminalis group and hybrids.

10. Leaves with rust-coloured hairs beneath: 40. atrocinerea and hybrids.

11. Stamens free: most species except 63. purpurea , 64. amplexicaulis , 67. caesia .

12. Stamens united: 63. purpurea , 64. amplexicaulis , 67. caesia .

13. Stamens 2: most species except 1. pentandra , 5. triandra .

14. Stamens 3: 5. triandra .

15. Stamens more than 3 (usually 5): 1. pentandra .

16. Ovary glabrous; 7. herbacea , (9-11). retusa group, 12. rotundifolia , (23-24). lanata group, 25. phylicifolia , (29-31). nigricans group, 32. glabra , 33. crataegifolia , 35. silesiaca , (49-51). repens group in part, 55. hastata , 56. pyrolifolia , 62. elaeagnos, 69. daphnoides , 70. acutifolia . Leaf-characters refer to adult leaves unless otherwise stated. Catkin-characters refer to the female catkins unless otherwise stated.

Literature: N. J. Andersson, Kungl. Svenska Vetensk. Akad. Handl. 6 (1): 1-180 (1867). N. J. Andersson in DC., Prodr. 16 (2): 191-323 (1868). R. Buser, Ber. Schweiz. Bot. Ges. 50: 567-788 (1940). A. & E. G. Camus, Jour. Bot. (Paris) 18: 177-213,245-96, 367-72 (1904); 19: 1 -68, 87-144 (1905); 20: 1 -116 (1906). B. Floderus in Holmberg, Handb. Skand . Fl. 1 (b, 1): 6-160 (1931). E. F. Linton, Jour. Bot. (London) 51: suppl. (1913). A. Toepfler, Ber. Bayer. Bot. Ges. 15: 17-233 (1915). F. Wimmer, Salices Europaeae . 1866.

1 Low shrub of the arctic or high mountains; catkins terminal or subterminal (see also 18-24 and 58-59)

2 Woody stem subterranean, with slender herbaceous leaf- and flower-bearing aerial stems

3 Leavesorbicularor reniform, usuallyemarginateat apex,

often wider than long, crenate-serrate; ovary glabrous

7. herbacea 3 Leaves broadly elliptical; margin entire or shallowly sinuate near the base; ovary tomentose 8. polaris 2 Woody stem above ground

4 Leaves with 2-5 pairs of lateral veins, usually orbicular

5 Petiole 5-15 mm; capsule tomentose 6. reticulata 5 Petiole 2-3 mm; capsule glabrous 12. rotundifolia 4 Leaveswith7 -8 pairsoflateralveins,usuallyovate,obovate or narrower

6 Ovary villous; twigs usually dark-coloured; catkins longpedunculate

7 Bracts with dark apex; leaves with prominent lateral veins

8 Stipules much longer than the very short petioles,

especially on the terminal leaves; leaves narrowly lanceolate, densely glandular-serrate; peduncle leafless

17. pulchra 8 Stipules much shorter than the petioles, often inconspicuous; leaves ovate or obovate, ±entire; peduncle leafy 16. arctica 7 Bracts uniformly pale; lateral veins ofleaves not prominent

9 Stipules absent; petiole 3-5 mm; bracts ferrugineous,

hairy on both surfaces 21. pyrenaica 9 Stipules as long as the petiole; petiole less than 3 mm or almost absent; bracts cibate, almost black in their upper part 22. reptans 6 Ovary glabrous or glabrescent; twigs brownish or greenish;

catkins sessile or subsessile

10 Leaves hairy, at least when young; catkins large, dark purple ( 13 -15). myrsinites group

10 Leaves usually glabrous, even when young; catkins small, greenish or yellowish (9-11). retusa group 1 Trees and shrubs usually of lower latitudes or lower altitudes; catkins lateral

11 Trees; bracts uniformly pale; flowers with2 or more nectaries, or male flowers with 2 and female with 1

12 Twigs long, slender, pendent (‘weeping willows’)

4. babylonica 12 Twigs not pendent

13 Mature leaves ± densely covered with persistent silky hairs 3. alba 13 Mature leaves completely glabrous

14 Leaves glossy above, finely and evenly serrate with yellow glands; stamens (4—)5(—12) 1. pentandra 14 Leaves not conspicuously glossy, rather coarsely serrate with white teeth; stamens (2-3)

15 Stipules persistent; bark of old stems flaking off; twigs not easily breaking off 5. triandra 15 Stipules usually caducous; bark of old stems not flaking off; twigs easily breaking off 2. fragilis 11 Shrubs; bractswithdarkapexandpalerbase; flowerswith one nectary

16 Filaments connate for at least half their length

17 Low shrub up to 1 m; leaves suborbicular or up to twice as long as wide; catkins less than 2 cm

18 Leaves suborbicular; peduncle c. 2 mm 68. tarraconensis 18 Leaves elliptical or obovate; ovary sessile or subsessile

67. caesia 17 Tall shrubs; leaves usually many times as long as wide; catkins 2 cm or more

19 Leaves lanate beneath at maturity; ovary glabrous

62. elaeagnos 19 Leaves ± glabrous beneath at maturity; ovary hairy

20 Young twigs and leaves ± densely silky

66. wilhelmsiana 20 Young twigs (and usually leaves) ± glabrous

21 Leaves with very prominent veins beneath 65. caspica 21 Leaves without prominent veins beneath

22 Leaves semi-amplexicaul or truncate at base, most or all opposite and sessile or subsessile

64. amplexicaulis 22 Leaves narrowed, cuneate or narrowly rounded at base, often alternate, often petiolate 63. purpurea 16 Filaments free (rarely connate in abnormal flowers)

23 Leaves usually ovate-lanceolate, elliptical or orbicular,

not many times as long as wide, glabrous, or with dull grey tomentum, or with white lanate tomentum of short irregularly arranged hairs (rarely somewhat silky and slightly shiny) beneath

24 Shrubs of subarctic or high mountains; branches usually thick, lanate, dark brown

25 Catkins, at least after flowering, with long, leafy peduncles; bracts uniformly pale; veins of leaves rather inconspicuous

26 Erect shrubs 1 -3 m; leaves rather large

(18-20). glauca group 26 Procumbent or ascending shrubs up to 50 cm; leaves small

27 Stipules absent; petiole 3-5 mm; bracts hairy on both surfaces, ferrugineous 21. pyrenaica 27 Stipules as long as petiole; petiole less than 3 mm or almost absent; bracts ciliate, almost black towards apex 22. reptans 25 Catkins always sessile or subsessile; bracts black towards apex; veins of leaves usually prominent

28 Stipules wide, persistent; leaves ovate, obovate or oblanceolate; ovary glabrous (23-24). lanata group 28 Stipules small, caducous; leaves usually ovatelanceolate; ovary tomentose (57-59). lapponum group 24 Shrubs or trees usually of lower latitudes or lower elevations

29 Leaves turning black on drying, glabrous or ± pubescent on both surfaces, green or glaucous beneath 30 Leavescoriaceous,glossy,with thickwaxy bloom over whole lower surface, including apex 32. glabra 30 Leaves not glossy, with waxy bloom beneath disappearing towards the apex or sometimes entirely lacking (29-31). nigricans group 29 Leaves neverturning black on drying, glabrous or densely pubescent beneath

31 Ovarysubsessile

32 Ovary glabrous

33 Twigs with a bluish waxy bloom 69. daphnoides 33 Twigs without a bluish waxy bloom

34 Petiole up to 10 mm, stout 55. hastata 34 Petiole 10-30 mm, slender

35 Leaves about twice as long as wide, silky beneath when young 33. crataegifolia 35 Leaves scarcely longer than wide, glabrous

56. pyrolifolia 32 Ovary pubescent(rarely glabrescent)

36 Pedicels 2-4 timesas long as nectary; catkins appearing with or after the leaves (25-28). phylicifolia group 36 Pedicels shorter than nectary or absent; catkins appearing before or with the leaves

37 Leaves dull on upper surface, ± entire; petioles

2-3 mm 67. caesia 37 Leaves shiny on upper surface, often serrate; petioles often more than 3 mm

(52-54). arbuscula group 31 Pedicel at least half as long as ovary

38 Ovary and pedicel glabrous

39 At least the main stems creeping; leaves rarely more than 2 cm, usually entire

40 Leaves usually rounded at both ends, finally glabrous; veins not or scarcely prominent above

48. myrtilloides 40 Leaves usually narrowed at both ends, ± persistently sericeous, at least beneath; veins fine but prominent above (49-51) repens group 39 Main stems erect; leaves more than 2 cm, never entire

41 Young twigs and leaves glabrous or almost so; inflorescence-axis with scattered short hairs; bracts with short hairs 35. silesiaca 41 Twigs and leaves with persistent thick felt; inflorescence-axis densely hairy; bracts with long white hairs 34. pedicellata 38 Ovaryandpedicelpubescent

42 Small shrub with at least the main stems creeping; leaves rarely more than 2 cm (49-51). repens group 42 Usually large shrub or small tree with ± erect stems; leaves usually more than 5 cm (but cf. 40, 41)

43 Leaves with shiny, appressed silky hairs on both surfaces 45. cantabrica 43 Leaves ± pubescent or glabrous, never with shiny silky hairs

44 Leaves 3-5 times as long as wide; stipules patent, with deflexed apex 44. salvifolia 44 Leaves normally less than 3 times as long as wide; stipules, if present, never patent with deflexed apex

45 2- to 4-year old twigs without or with few scarcely prominent ridges beneath the bark

46 Leaves ± glabrous beneath; shrub less than

1 m (46-47). starkeana group 46 Leaves persistently hairy beneath; usually more than 1 m

47 Leaves l |- 2 times as long as wide, ovate or obovate to ovate-oblong; no ridges beneath the bark (42-43). caprea group 47 Leaves usually more than twice as long as wide, obovate to oblanceolate or narrowly elliptical; scattered ± indistinct ridges usually present beneath the bark

48 Stipules usually absent (46-47). starkeana group 48 Stipules well developed

49 Twigs grey-brown or grey, with flat leafscars; mature leaves rather thick, veins closely reticulate, impressed above, prominent beneath 37. appendiculata

49 Twigs blackish with protruding leaf-scars;

mature leaves thin, veins widely reticulate,

± prominent above, scarcely prominent beneath 38. laggeri

45 2- to 4-year old twigs with numerous very prominent ridges beneath the bark

50 Buds and twigs of the previous year pubescent

51 Ridges beneath the bark short, discontinuous;

leaves finally ± glabrous above, and with sparse grey persistent indumentum beneath

36. aegyptiaca

51 Ridges beneath the bark long, continuous;

leaves persistently but sparsely pubescent above, and with dense grey felted persistent indumentum beneath 39. cinerea

50 Buds and twigs of the previous year ± glabrous

52 Catkins 1-2-5 cm; leaves c. 2-3 cm, rugose,

grey, ± tomentose beneath 41. aurita

52 Catkins 2-5 cm; leaves 3 cm or more, not rugose,

sparsely pubescent beneath; hairs, especially along the veins, rust-coloured 40. atrocinerea 23 Leaves usually narrow, linear-lanceolate or oblonglanceolate, many times as long as wide; glabrous, or lower surface with silky appressed hairs all longitudinally arranged 53 Young twigs with a bluish waxy bloom; mature leaves glabrous, serrate; ovary glabrous 54 Leaves oblong-lanceolate to oblong-ovate, acute or shortly acuminate; lateral veins 8-12 pairs; bracts about as long as ovary 69. daphnoides 54 Leaves lanceolate to linear-lanceolate, long-acuminate;

lateral veins 15 or more pairs; bracts c. | as long as ovary 70. acutifolia 53 Young twigs without a waxy bloom; leaves silky beneath,

entire; ovary silky 55 Usually low shrubs of swamps, bogs or damp sand;

style short; catkins rarely as much as 2-5 cm

(49-51). repens group 55 Tall riverside shrubs or small trees; style ± long; catkins more than 2-5 cm (60-61). viminalis group