Neotropical Salicaceae

Description

Trees or shrubs, with or without thorns or spines. Leaves alternate or rarely opposite or subopposite (Abatia Ruiz & Pav.), simple, pinnately or palmately veined, sometimes acrodromous perfect (3-veined from base to apex: Lunania Hook., Neosprucea Sleumer); margins entire to crenate, serrate, dentate, or spinose; leaf teeth, if present, with small conical, deciduous appendages or with persistent, papillate to globose to torus-(doughnut-)shaped glands; infrequently with stellate pubescence (some Abatia, Banara Aubl., Macrohasseltia L.O.Williams, Pineda Ruiz & Pav., Ryania Vahl); lamina sometimes with pellucid-punctations or -lines (tribe Samydeae); exstipulate or stipulate, stipules sometimes large and falcate (e.g., Prockia P.Browne ex L., Salix L.) or even leaf-like (Azara Ruiz & Pav.). Sexuality various, usually hermaphroditic, polygamous, or dioecious. Inflorescences axillary or terminal, catkins, spikes, racemes, panicles, cymes, corymbs, umbelliform cymes, fascicles, or glomerules, or reduced to single flowers. Flowers actinomorphic or irregular (tribe Saliceae), often minute. Hypanthium present or absent. Sepals absent (tribe Saliceae), otherwise 3-15(-22), aestivation imbricate or valvate. Petals absent or 3-8(-12), aestivation imbricate or valvate. Disk sometimes present, in some groups appearing like thick staminodes and in other groups like globose nectaries, inside, alternating with, or outside the stamens. Stamens (1-)2-numerous, sometimes in epipetalous bundles; anthers globose to linear-elongate; anther dehiscence introrse (tribe Samydeae), extrorse, or latrorse (Lunania), dehiscence usually longitudinal (± poricidal in Neosprucea). Gynoecium of 1 pistil, ovary superior or half-inferior (Homalium Jacq.), generally unilocular (occasionally with septa in Dovyalis E.Mey. ex Arn., Flacourtia L'Her., Hasseltia Blume, Prockia), placentation parietal or pseudo-axile, styles 1-8, stigma capitate to lacerate to obscure. Fruit a fleshy or dry berry, capsule, samara (Neopringlea S.Watson), or drupe (Flacourtia). Seeds 1-numerous, arillate or exarillate, sometimes covered in cottony hairs (Bartholomaea Standl. & Steyerm., Casearia Jacq. sect. Gossypiospermum Urb., Macrohasseltia) or with a coma (Populus L., Salix).

Notes on delimitation

• Salicaceae were traditionally a mostly temperate family consisting of two genera, Populus (poplars, cottonwoods, aspens) and Salix (willows).
• Recent phylogenetic analyses using DNA sequence data, however, indicate that Salicaceae sensu stricto are nested within the non-cyanogenic taxa of the former Flacourtiaceae. These taxa have now been united into one family, the Salicaceae (Eurosids I: Malpighiales), which is closely related to Lacistemataceae, Passifloraceae, Violaceae, Achariaceae, and allied families.
• Some botanists (the author included) prefer to segregate one tribe of Salicaceae sensu lato as a separate family (Samydaceae), leaving the rest as a Salicaceae sensu medio, but this approach has not been widely accepted.
• The former Flacourtiaceae have been a notorious family, principally because Flacourtiaceae are diverse morphologically and because the family has served as a garbage can for taxa of uncertain affinity. Several key studies in the past 30 years have mostly eliminated the latter problem, but unfortunately, the former "problem" continues to persist in the current Salicaceae sensu lato. Thus, for the novice, the description and advice of Al Gentry is pertinent: "One of the two most notoriously heterogeneous neotropical families. A good dictum for the beginner is: 'If you don't have any idea what family it is, try Flacourtiaceae [now mostly Salicaceae sensu lato] or Euphorbiaceae'" (Gentry, 1993).

Distribution in the Neotropics

• Abatia Ruiz & Pav. (including Aphaerema Miers):  montane Central and South America, SE Brazil.
• Azara Ruiz & Pav.:  Chile, Argentina, Bolivia, and SE Brazil, mostly subtropical and temperate.
• Banara Aubl.:  Antilles, Mexico, Central and South America, especially diverse in the Antilles.
• Bartholomaea Standl. & Styerm.:  Mexico, Guatemala, and Belize.
• Casearia Jacq.:  Antilles, Mexico, Central and South America.
• Dovyalis E.Mey.:  cultivated for fruit, throughout.
• Euceraea Mart.:  South America.
• Flacourtia L.'Her.:  cultivated for fruit, throughout.
• Hasseltia Blume:  Central and South America.
• Hasseltiopsis Sleumer:  Central America.
• Hecatostemon S.F.Blake:  northern South America.
• Homalium Jacq.:  Antilles, Mexico, Central and South America.
• Laetia Loefl.:  Antilles, Central and South America.
• Lunania Hook.:  Antilles, Central and South America, most diverse in the Antilles.
• Macrohasseltia L.O.Williams:  Central America.
• Macrothumia M.H.Alford:  Brazil.
• Neopringlea S.Watson:  Mexico and Guatemala.
• Neoptychocarpus Buchheim: South America.
• Neosprucea Sleumer:  Panama and South America.
• Olmediella Baill.:  Mexico and Central America.
• Pineda Ruiz & Pav.:  montane Ecuador, Peru, and Bolivia.
• Pleuranthodendron L.O.Williams:  Central and South America.
• Populus L.:  Mexico, but infrequently cultivated elsewhere.
• Prockia P.Beowne ex L.:  Antilles, Mexico, Central and South America.
• Ryania Vahl:  Central and South America.
• Salix L.: Mexico, Central and South America.
• Samyda Jacq.:  Antilles, Mexico, and Central America.
• Tetrathylacium Poepp. & Endl.:  Central and South America.
• Xylosma G.Forst. (including Priamosia Urb.):  Antilles, Mexico, Central and South America.
• Zuelania A.Rich.:  Antilles, Central and northern South America.

Distinguishing characters (always present)

• Trees or shrubs.
• Leaves simple.

Other important characters

• Placentation usually parietal (axile or pseudo-axile in few genera).
• Leaves pellucid-punctate or -lineate in tribe Samydeae.
• Leaves usually alternate (except opposite in Abatia) and commonly toothed.
• Non-cyanogenic.

Key differences from similar families

• Salicaceae can be confused with a large number of other families. They are commonly mistaken for Euphorbiaceae, Violaceae, or Malvales.
• Unlike Euphorbiaceae, many common Salicaceae have torus- (or doughnut-) shaped glands at the leaf teeth and never produce a milky latex.
• Salicaceae can usually be distinguished from Malvales if flower or fruit (and placentation) is available, but even then, some Salicaceae have highly intruded to pseudo-axile placentation; few Salicaceae also have stellate pubescence and petiolar pulvini, although not both in the same species (as currently known).
• Salicaceae tend to have more stamens (>5) and less elongate fruit than Violaceae.
• Infrequently, species of Salicaceae with pellucid -punctuations or -lines may be confused with Rutaceae, but the leaves of Rutaceae are usually compound and the flowers usually have an intrastaminal, annular nectary disk.
• The opposite-leaved Abatia is easily confused with Buddleja L. (Buddlejaceae) or Viburnum L.(Adoxaceae) in the vegetative state; again, leaf teeth are helpful. In flower, they can be distinguished because Abatia lacks petals and generally has more than 5 stamens, all free.
• Tribe Saliceae (Populus and Salix) may be confused with Lacistemataceae, a closely related family with catkin (or catkin -like) inflorescences. Lacistemataceae usually have bisexual flowers, some perianth, arillate seeds, and a single stamen with an expanded connective. Populus and Salix rarely have one stamen, are usually dioecious, apparently lack perianth (minute in Populus and only clear early in development), and generally have two or more stamens.

Number of genera

• Abatia (including Aphaerema Miers) - 10 spp.
• Azara - 10 spp.
• Banara - ca. 35 spp.
• Bartholomaea - 2 spp.
• Casearia (sometimes placed in Samydaceae) - ca. 180 spp. worldwide, ca. 80 in the Neotropics.
• Dovyalis - ca. 15 spp. worldwide, 1 sp. infrequently cultivated in the Neotropics.
• Euceraea (sometimes placed in Samydaceae) - 3 spp.
• Flacourtia - ca. 15 spp. worldwide, 1(+?) sp. infrequently cultivated in the Neotropics.
• Hasseltia - 4 spp.
• Hasseltiopsis - 1 sp.
• Hecatostemon (sometimes placed in Samydaceae) - 1 sp.
• Homalium - ca. 200 worldwide, 3 in the Neotropics.
• Laetia - 10 spp.
• Lunania (sometimes placed in Samydaceae) - 14 spp.
• Macrohasseltia - 1 sp.
• Macrothumia - 1 sp.
• Neopringlea - 3 spp.
• Neoptychocarpus (sometimes placed in Samydaceae) - 2 spp.
• Neosprucea - 9 spp.
• Olmediella - 1 sp.
• Pineda - 2 spp.
• Pleuranthodendron - 1 sp.
• Populus - ca. 32 spp. worldwide, ca. 4 spp. in the Neotropics (2 native, 2 introduced and naturalized).
• Prockia - ca. 6 spp.
• Ryania (sometimes placed in Samydaceae) - ca. 8 spp.
• Salix - ca. 450 spp. worldwide, 17 in the Neotropics (11 native, 5 introduced and 1 naturalized).
• Samyda (sometimes placed in Samydaceae) - 9 spp.
• Tetrathylacium (sometimes placed in Samydaceae) - 2 spp.
• Xylosma (including Priamosia Urb.) - ca. 95 spp. worldwide, ca. 50 in the Neotropics.
• Zuelania (sometimes placed in Samydaceae) - 1 sp.

Useful tips for generic identification

Key to genera of Neotropical Salicaceae

See also Alford (2003) for an even more superficial key (Populus and Salix were not included; Macrothumia is treated as Banara; and a new species of Pineda keys incorrectly).

1. Leaves opposite ... Abatia
1. Leaves alternate … 2

2. Leaves 3-7-veined from the base … 3
2. Leaves pinnately veined … 18

3. Inflorescences of catkins, spikes, compound spikes, spike-like racemes, or panicles of spikes; leaves sometimes pellucid-punctate or -lineate … 4
3. Flowers solitary or inflorescences of fascicles, lax racemes, panicles, cymes, or compound umbelliform cymes; leaves never pellucid-punctate or -lineate … 7

4. Flowers unisexual; seeds with cottony pubescence; leaf margin usually crenate … 5
4. Flowers bisexual; seeds arillate; leaf margin usually entire or subserrate ... Lunania

5. Sepals present; inflorescences axillary and peduncled .... Bartholomaea
5. Sepals apparently absent; inflorescences sessile or terminating a leafy branch … 6

6. Buds with 3-10 overlapping scales, often resinous; nectary disk or glands lacking .... Populus
6. Buds with 1 scale, not resinous; disk gland(s) (nectary or nectaries) present .... Salix

7. Anthers linear-elongate, anther dehiscence ± poricidal; leaves often 3-veined from base to near apex with perpendicular tertiary veins... Neosprucea
7. Anthers globose, anther dehiscence longitudinal; leaves 3-veined from base to no more than 2/3 leaf length … 8

8. Fruit a capsule; seeds with cottony pubescence .... Macrohasseltia
8. Fruit a berry (rarely tardily dehiscent), drupe, or samara; seeds lacking cottony pubescence … 9

9. Dioecious; styles or style branches 4-8 … 10
9. Hermaphroditic (rarely polygamous or functionally androdioecious in Prockia); style … 13

10. Petals present in male flowers; unarmed; native … 11
10. Petals absent in male flowers; frequently with thorns on the trunk or branches; cultivated and possibly naturalised … 12

11. Fruit a samara; stamens in bundles of 3 alternating with disk glands; petals lacking in female flowers ... Neopringlea
11b. Fruit a berry; stamens numerous (>20), not in bundles; petals present in female flowers ... Hasseltiopsis

12. Fruit a drupe; disk glands in a row outside the stamens; leaves (in Neotropical cultivated sp.) glabrous or glabrescent ... Flacourtia
12. Fruit a pubescent berry; disk glands alternating with stamens; leaves (in Neotropical cultivated sp.) with pubescence visible with the naked eye, especially on the veins... Dovyalis

13. Glands at leaf teeth (at maturity) abaxial and doughnut (= torus) shaped; disk glands< /A> lacking … 14
13. Glands at leaf teeth, if present, marginal and papillate; disk glands present … 15

14. Inflorescence a raceme; placentation often pseudo-axile; petals sometimes lacking; stipules sometimes foliaceous; sexuality various ... Prockia
14. Inflorescence a panicle, raceme, or fascicle; placentation parietal to highly intruded parietal; petals present; stipules small, caducous; bisexual... Banara

15. Glands near apex of petiole, if present, usually not paired and not opposite each other; outer row of filamentous staminodes present .... Pineda
15. Glands at base of lamina or near apex of petiole paired and opposite each other; filamentous staminodes lacking … 16

16. Placentation axile or pseudo-axile; perianth persistent in fruit; a pair of elliptic leaf glands embedded in the base of the lamina... Hasseltia
16. Placentation parietal; perianth deciduous in fruit; a pair of cicular leaf glands projecting from the lamina-petiole junction or apex of the petiole … 17

17. Inflorescence a panicle; seed(s) 1 (or 2) per fruit... Pleuranthodendron
17. Inflorescence a raceme, this sometimes congested and fascicle- or umbel-like; seeds per fruit numerous ... Macrothumia

18. Leaf margins spinose … 19
18. Leaf margins entire, crenate, or serrate … 20

19. Dioecious; sepals 7-15(-22); stamens numerous; leaves not pellucid-punctate or -lineate .... Olmediella
19. Bisexual; sepals 5-6; stamens 6-10; leaves sometimes pellucid-punctate or -lineate .... Casearia sect. Casearia informal group 'Ilicifoliae' … 20

20. Flowers lacking any obvious perianth; inflorescences of catkins; fruits capsules; seeds with cottony pubescence … 21
20. Flowers with at least sepals present; inflorescences various, not catkins; fruits generally berries or tardily deshicent capsules; seeds usually lacking cottony pubescence (except Casearia sect. Gossypiospermum) … 22

21. Buds with 3-10 overlapping scales, often resinous; nectary disk or glands lacking .... Populus
21b. Buds with 1 scale, not resinous; disk gland(s) (nectary or nectaries) present .... Salix

22. Ovary inferior or semi-inferior ... Homalium
22. Ovary superior … 23

23. Inflorescences of spikes, compound spikes, or panicles of spikes … 24
23. Flowers solitary or inflorescences of fascicles, racemes, cymes, or panicles … 26

24. Leaves pellucid-punctate or -lineate; stamens 8 ... Euceraea
24. Leaves not pellucid-punctate or -lineate; stamens 4 or 10-20 … 25

25. Stamens 10-20; foliaceous stipules sometimes present; leaves <10 cm long; sepals generally yellow ... Azara
25. Stamens 4; stipules not foliaceous; leaves >8 cm long; sepals generally white or red ... Tetrathylacium

26. Petals present … 27
26. Petals absent … 28

27. Sepals and petals generally 3; disk glands lacking; outer filamentous staminodes lacking .... Banara
27. Sepals and petals (4-) 5 (-6); disk glands present; outer filamentous staminodes present .... Pineda

28. Thorns on trunks or branches present … 29
28. Thorns on trunks or branches absent … 33

29. Flowers usually unisexual; sepals free; leaves not pellucid-punctate or -lineate … 30
29. Flowers bisexual; sepals united at the base (sometimes up to 1/3 or more) with stamens forming a hypanthium; leaves usually pellucid-punctate and/or -lineate … 32

30. Styles, style branches, or stigmas 1-3(-5); native .... Xylosma
30. Styles, style branches, or stigmas (2-)5-12; cultivated and possibly naturalised … 31

31. Fruit a glabrous drupe; disk glands in a ring outside the stamens; style branches 4-6 (each with bilobed stigmas) .... Flacourtia
31. Fruit a pubescent berry; disk glands alternating with the stamens; style branches 5(-7) .... Dovyalis

32. Disk lobes and stamen filaments free or only united near the base; flowers few to numerous per inflorescence.... Casearia sect. Casearia -OR- Casearia sect. Guidonia
32. Disk lobes and stamen filaments united almost completely or disk lobes apparently absent; flowers generally 1-3 per inflorescence.... Samyda

33. Glands present at the base of the leaves or on petioles … 34
33. Glands absent at the base of the leaves or on petioles … 35

34. Stipules absent (or apparently so); sepals 4-6; style branches or stigmas 1-3(-5) .... Xylosma
34. Stipules present; sepals 7-15(-22); style branches or stigmas 6-8 .... Olmediella

35. Bracts united into a cup below the flowers and fruits … 36 
35. Bracts free … 37

36. Stamens 30-50; seeds arillate; fruits frequently with rust-colored pubescence .... Laetia sect. Scypholaetia
36. Stamens 8-10; seeds exarillate, covered in cottony pubescence; fruits glabrous.... Casearia sect. Gossypiospermum

37. Leaves never pellucid-punctate or -lineate; glands at leaf teeth (if leaves toothed) usually abaxial, torus-shaped, and persistent; disk glands present, globose, nectariferous; anther dehiscence extrorse; seeds exarillate … 38
37. Leaves usually pellucid-punctate or -lineate; glands at leaf teeth (if leaves toothed) usually marginal, conical or hair-like, and deciduous; disk glands absent or present, if present, in the shape of ligulate staminodes, not nectariferous; anther dehiscence introrse; seeds usually arillate … 40

38. Leaf-like stipules (i.e., two "leaves" of different shape or size at a node) usually present; inflorescences spikes, racemes, corymbs, or fascicles; style 1; outer filamentous staminodes often present .... Azara
38. Leaf-like stipules absent; inflorescences fascicles or short racemes; styles or style branches 1-7; outer filamentous staminodes lacking … 39

39. Styles, style branches, or stigmas 5-7; cultivated .... Dovyalis
39. Styles, style branches, or stigmas 1-3(-5); native .... Xylosma

40. Dioecious; sepals 4, obviously connate; leaves entire, glabrous.... Neoptychocarpus
40. Bisexual; sepals 4-5(-9), connate or free; leaves entire or toothed, glabrous or pubescent … 41

41. Disk glands absent or obscure … 42
41. Disk glands present … 43

42. Sepals fused into a tube, at least basally, usually more .... Samyda
42. Sepals free.... Laetia

43. Stamens 5-12(-22), often included within the sepals .... Casearia
43. Stamens 20-100, usually exposed … 44

44. Anthers linear-elongate; disk inside the stamens; stellate hairs on the leaves commonly present .... Ryania
44. Anthers globose; disk glands inside or alternating with the stamens; hairs simple … 45

45. Stamens 20-40; stigma peltate.... Zuelania
45. Stamens 80-100; stigma small, capitate.... Hecatostemon

Notable genera and distinguishing features

• Abatia - opposite leaves, generally montane.
• Azara - commonly has leaf-like stipules, generally subtropical to temperate in the south.
• Banara - common genus, especially along rivers or in disturbed areas.
• Casearia - common genus, inflorescences usually axillary fascicles, leaves with pellucid -punctations or -lines, seeds arillate (sometimes confused with Xylosma, which lacks the pellucid-punctations, has unisexual flowers, and has free [and sometimes more numerous] stamens [visible as remnants even in fruit]; also, Casearia, when toothed, has deciduous conical leaf teeth ( Xylosma) typically has abaxial, persistent, glandular, doughnut or spherical shaped teeth).
• Hasseltia and Pleuranthodendron - common genera in Central America and northern South America; both have 3-veined leaves with paired glands at base of lamina or apex of petiole (see photo in Alford, 2003).
• Populus and Salix - generally temperate genera that have unisexual flowers in catkins, flowers have no evident calyx or corolla, and seeds have a coma: a specific structure with a circular bolster with unicellular cotton-like trichomes connected from below.
• Prockia - common genus, especially in disturbed or seasonally dry areas, 3-merous flowers.
• Xylosma - common genus, generally dioecious, occasionally with thorns or spines, flowers usually in axillary fascicles (see Casearia for confusion).

Status

• Abatia (including Aphaerema) - Endemic
• Azara - Endemic
• Banara - Endemic
• Bartholomaea - Endemic
• Casearia - Native
• Dovyalis - Cultivated
• Euceraea - Endemic
• Flacourtia - Cultivated
• Hasseltia - Endemic
• Hasseltiopsis - Endemic
• Hecatostemon - Endemic
• Homalium - Native
• Laetia - Endemic
• Lunania - Endemic
• Macrohasseltia - Endemic
• Macrothumia - Endemic
• Neopringlea - Endemic
• Neoptychocarpus - Endemic
• Neosprucea - Endemic
• Olmediella - Endemic
• Pineda - Endemic
• Pleuranthodendron - Endemic
• Populus - Native, cultivated and naturalized.
• Prockia - Endemic
• Ryania - Endemic
• Salix - Native, cultivated and naturalized.
• Samyda - Endemic
• Tetrathylacium - Endemic
• Xylosma (including Priamosia) - Native
• Zuelania - Endemic

General notes

• Berberidopsis Hook.f. is treated under Berberidopsidaceae.
• Lacistema Sw. and Lozania Mutis ex Caldas are treated under Lacistemataceae.
• Cyanogenic (former) Flacourtiaceae are treated under Achariaceae.
• In general, tropical members of the family Salicaceae have few economic uses.
• The more temperate genus Populus is fast-growing, used for wood, and now includes the first woody species to have its entire genome sequenced.
• The mostly temperate genus Salix is one of the early sources of aspirin precursors.
• Salix species (willows) are very important in management of ecosystems such as prevention of erosion, bioremediation of soil and they provide a specialised habitat for other organisms.
• Some willows are widely cultivated as ornamental plants and used in wicker furniture.
• Both Salix and Populus are potential biofuel sources.
• In the Neotropics, genera like Casearia and Macrohasseltia are occasionally used for wood, and the genus Ryania has toxic compounds used in poisons and insecticides.
• Despite their lack of use in the Neotropics, Salicaceae are common elements of tropical forests.

Important literature

Alford, M. H. 2003. Claves para los gιneros de Flacourtiaceae de Perϊ y del Nuevo Mundo. Arnaldoa 10(2): 19-38.

Argus, G.W. 1997.  Infra-generic classification of Salix (Salicaceae) in the New World. Syst. Bot. Monogr. 52: 1-121.

Chase, M. W., S. Zmarzty, M. D. Lledo, K. J. Wurdack, S. M. Swensen, & M. F. Fay. 2002. When in doubt, put it in Flacourtiaceae: a molecular phylogenetic analysis based on plastid rbcL DNA sequences. Kew Bulletin 57: 141-181.

Eckenwalder, J.E. 1996. Systematics and evolution of Populus in: Stettler, R.F., Bradshaw, H.D., Heilman, P.E. & Hinckley, T.M. Biology of Populus and its implications for management and conservation 1(1): 7-32.

Gentry, A. H. 1993. A Field Guide to the Families and Genera of Woody Plants of Northwest South America (Colombia, Ecuador, Peru) with Supplementary Notes on Herbaceous Taxa. Chicago: University of Chicago Press.

Lemke, D. E. 1988. A synopsis of Flacourtiaceae. Aliso 12: 29-43.

Schneider, C. K.  1918.  A conspectus of Mexican, West Indian, Central and South American varieties of Salix.  Bot. Gaz. 65: 1-41.

Sleumer, H. O. 1980. Flacourtiaceae. Flora Neotropica No. 22. Bronx: New York Botanical Garden.

How to cite

Alford, M.H. & Belyaeva, I.V. (2009). Neotropical Salicaceae. In: Milliken, W., Klitgεrd, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Salicaceae.htm.