Croton

Herbs, subshrubs, or shrubs [trees], annual or perennial, monoecious or dioecious; hairs stellate or scalelike; latex colorless to reddish [absent]. Leaves persistent, semideciduous, or drought deciduous, alternate, simple, often with lemony, pungent, or acrid odor when crushed, older leaves often turning orange before falling; stipules absent or present, persistent, deciduous, or caducous; petiole present [absent], glands present at apex or absent; blade unlobed [palmately lobed], margins entire, crenate, denticulate, serrulate, or serrate-dentate, laminar glands absent [at base, on margins or abaxial surface]; venation pinnate or palmate at base, pinnate distally. Inflorescences unisexual or bisexual (pistillate flowers proximal, staminate distal), terminal or axillary, spikes, racemes, or thyrses; glands subtending each bract 0. Pedicels present or absent. Staminate flowers: sepals (3–)5(–6), valvate or slightly imbricate, distinct or connate basally; petals (3–)5(–6) or 0, distinct, white; nectary extrastaminal, usually 5 glands; stamens 3–35[–50], inflexed in bud, distinct; pistillode absent. Pistillate flowers: sepals [3–](4–)5(–9)[–10] or 0, imbricate or valvate, distinct (connate for 1/2+ length in C. argyranthemus); petals 5 (sometimes rudimentary) or 0, distinct or connate basally, white or pale green; nectary annular, 5 glands, or absent; pistil (1–)3-carpellate; styles (1–)3, distinct or connate basally, unbranched, 2-fid, or multifid. Fruits usually capsules (achenes in C. michauxii). Seeds ellipsoid, oblong, ovoid, globose, or lenticular; caruncle present. x = 8, 9, 10, 14.

Distribution

North America, Mexico, West Indies, Bermuda, Central America, South America, Asia, Africa, Indian Ocean Islands, Pacific Islands, Australia, most diverse in dry tropical and warm-temperate regions.

Discussion

Species ca. 1250 (31 in the flora).

Croton species are the main larval food of the leafwing butterfly (Anaea spp.) and some related genera. Their seeds are also a favorite food for doves and other birds. The circumscription of Croton was consolidated by the molecular phylogeny of P. E. Berry et al. (2005), which separated C. lobatus into the genus Astraea and confirmed the inclusion of the genera Crotonopsis Michaux, Eremocarpus Bentham, and Julocroton Martius as sections of Croton. The molecular phylogeny and sectional treatment of B. W. van Ee et al. (2011) further updated the sectional taxonomy of G. L. Webster (1993) for the New World species.

Croton trinitatis Millspaugh, native to Central and South America, was collected once (in 1886) on ballast piles in Pensacola, Florida, but has not been reported in the flora area since. It keys with C. glandulosus, from which it differs in its larger, more deltate leaves with deeper, sharper marginal teeth. Croton bonplandianus Baillon, which is native to Argentina and Paraguay and naturalized elsewhere, was collected several times in the 1950s on ballast ore piles in the ports of Baltimore, Maryland, and Newport News, Virginia (C. F. Reed 1964), but does not appear to have persisted there. Croton bonplandianus would also key with C. glandulosus but differs in its larger, shallowly serrate-margined, narrowly ovate leaves; inflorescences 5–14 cm; and sessile glands at the base of the leaf blade.

Selected References

Berry, P. E. et al. 2005. Molecular phylogenetics of the giant genus Croton (Euphorbiaceae sensu stricto) using ITS and trnL–F DNA sequence data. Amer. J. Bot. 92: 1520–1534.

Ferguson, A. M. 1901. Crotons of the United States. Rep. (Annual) Missouri Bot. Gard. 1901: 33–73.

van Ee, B. W. and P. E. Berry. 2009. The circumscription of Croton section Crotonopsis (Euphorbiaceae), a North American endemic. Harvard Pap. Bot. 14: 61–70.

van Ee, B. W. and P. E. Berry. 2010. Taxonomy and phylogeny of Croton section Heptallon (Euphorbiaceae). Syst. Bot. 35: 151–167.

van Ee, B. W., R. Riina, and P. E. Berry. 2011. A revised infrageneric classification and molecular phylogeny of New World Croton (Euphorbiaceae). Taxon 60: 791–823.

Webster, G. L. 1993. A provisional synopsis of the sections of the genus Croton (Euphorbiaceae). Taxon 42: 793–823.

Lower Taxa

Croton alabamensis, Croton argenteus, Croton argyranthemus, Croton californicus, Croton capitatus, Croton ciliatoglandulifer, Croton cortesianus, Croton coryi, Croton dioicus, Croton elliottii, Croton fruticulosus, Croton glandulosus, Croton heptalon, Croton humilis, Croton incanus, Croton leucophyllus, Croton lindheimeri, Croton lindheimerianus, Croton linearis, Croton michauxii, Croton monanthogynus, Croton parksii, Croton pottsii, Croton punctatus, Croton sancti-lazari, Croton setigerus, Croton soliman, Croton sonorae, Croton suaveolens, Croton texensis, Croton wigginsii

Key

1	Leaf blade margins coarsely crenate to serrate-dentate; petioles with 2 cuplike glands at apex.	Croton glandulosus
1	Leaf blade margins entire, denticulate, or serrulate; petioles without cuplike glands at apex (sessile or stipitate glands often present at apex in C. linearis, stipitate-glandular in C. ciliatoglandulifer).	> 2
2	Shrubs; leaf blade abaxial surfaces densely lepidote; pistillate petals 5, ovate, pale green; styles 3, usually unbranched, rarely 2-fid.	Croton alabamensis
2	Herbs, subshrubs, or shrubs; if shrubs, leaf blade abaxial surfaces mainly stellate-hairy or stellate-tomentose, seldom stellate-lepidote; pistillate petals 0, rudimentary, or, if 5 (sometimes in C. humilis and C. soliman), linear or subulate, white; styles 2–3, 2-fid to multifid, or 1, unbranched.	> 3
3	Ovaries 1-locular; styles unbranched; leaves mostly clustered near inflorescences; annual herbs.	Croton setigerus
3	Ovaries 2–3-locular; styles 2-fid or multifid; leaves clustered near inflorescences or not; annual or perennial herbs, subshrubs, or shrubs.	> 4
4	Leaf blade abaxial surfaces densely lepidote or stellate-lepidote, often silvery.	> 5
5	Inflorescences bisexual; staminate petals 5; columella 3-angled (not markedly 3-winged) or absent (when fruit an achene); annual or perennial herbs or subshrubs.	> 6
6	Leaf blades on proximal parts of stems oval to narrowly obovate, on distal parts oblong to lanceolate-oblong or broadly elliptic, apex obtuse to rounded, adaxial surface sparsely lepidote or glabrate; inflorescences racemes; ovaries 3-locular; fruits capsules; staminate sepals 5 mm, petals 5 mm, pedicels 1–5 mm; pistillate sepals connate for 1/2+ length.	Croton argyranthemus
6	Leaf blades lanceolate-linear to ovate-lanceolate, apex acute, adaxial surface sparsely stellate-hairy; inflorescences spikes; ovaries 1-locular; fruits achenes; staminate sepals 1 mm, petals 0.6–1 mm, pedicels 0–1 mm; pistillate sepals distinct.	Croton michauxii
5	Inflorescences usually unisexual (sometimes bisexual in C. punctatus); staminate petals 0; columella 3-winged; subshrubs or shrubs.	> 7
7	Plants monoecious (sometimes appearing dioecious); leaf blades more than 1/2 as wide as long, petioles 1/2 to as long as leaf blade; Atlantic and Gulf coasts.	Croton punctatus
7	Plants dioecious; leaf blades usually less than 1/2 as wide as long, petioles usually less than 1/2 as long as leaf blade; c Texas to California.	> 8
8	Subshrubs, 2–5(–9) dm; petioles 0.2–0.8(–2) cm; New Mexico, Texas.	Croton dioicus
8	Shrubs, 4–11 dm; petioles 1–4(–4.5) cm; Arizona, California, Nevada, Utah.	> 9
9	Pedicels of pistillate flowers less than or equal to 1 mm (1–3 mm in fruit); seeds 4–5.5 × 3.5–5.5 mm; Arizona, California, Nevada, Utah.	Croton californicus
9	Pedicels of pistillate flowers 1–2 mm (4–7 mm in fruit); seeds 6.5–7 × 2–3 mm; sw Arizona, se California.	Croton wigginsii
4	Leaf blade abaxial surfaces usually stellate-hairy, if stellate-lepidote not markedly silvery.	> 10
10	Annual herbs.	> 11
11	Plants dioecious; inflorescences unisexual; staminate petals 0; capsules verrucose, columella 3-winged.	> 12
12	Plants 5–15 dm; leaf blade abaxial surfaces densely stellate-tomentose; capsules 8–9 mm; s Texas.	Croton parksii
12	Plants 2–7(–9) dm; leaf blade abaxial surfaces densely appressed stellate-hairy; capsules 5–8 mm; widespread in s and c United States, mostly not s Texas.	Croton texensis
11	Plants monoecious; inflorescences bisexual or unisexual; staminate petals 3–5; capsules smooth, columella not markedly 3-winged (usually 3-angled or apex with 3 lobes).	> 13
13	Leaf blade abaxial surfaces appearing brown-dotted, some stellate hairs with dark brown centers; stamens 3–5; styles 2, 2-fid, terminal segments 4; ovaries 2-locular, only 1 fertile.	Croton monanthogynus
13	Leaf blade abaxial surfaces not appearing brown-dotted, no stellate hairs with brown centers; stamens 7–16; styles 3, 2-fid or multifid, terminal segments 6–18(–24); ovaries 3-locular.	> 14
14	Pistillate sepal margins laciniate.	Croton argenteus
14	Pistillate sepal margins entire.	> 15
15	Inflorescences 4–7 cm; staminate flowers 15–25, sepals 3 mm, petals 3–3.5 mm, stamens 14–16; pistillate flowers 8–15.	Croton coryi
15	Inflorescences 0.5–4 cm; staminate flowers 1–15, sepals 0.8–2 mm, petals 0.8–1.5 mm, stamens 7–13; pistillate flowers 1–8.	> 16
16	Pistillate sepals 5–6; styles 2-fid, terminal segments 6; herbs 1–5 dm.	> 17
17	Pistillate sepals unequal, 3 outer 5–7 mm, 2 inner 1–2 mm.	Croton leucophyllus
17	Pistillate sepals equal, 3 mm.	Croton lindheimerianus
16	Pistillate sepals 6–9; styles multifid, terminal segments 12–18(–24); herbs 3–20 dm.	> 18
18	Leaf blades 0.2–0.8 cm wide, if wider then pistillate sepal apices recurved; staminate sepals and petals 0.8–1 mm; styles 2–3 mm.	> 19
19	Leaf blades ovate to lanceolate-elliptic, 3–8(–15) × 1–4 cm; pistillate sepals 7–10(–15 in fruit) mm, apices recurved.	Croton capitatus
19	Leaf blades lanceolate to oblong, 2–5.5 × 0.2–0.8 cm; pistillate sepals 5–6 mm, apices incurved.	Croton elliottii
18	Leaf blades 1–5 cm wide, pistillate sepal apices straight or slightly incurved; staminate sepals 1–2 mm, petals 1–1.5 mm; styles 3–4 mm.	> 20
20	Pistillate sepals whitish appressed-tomentose; styles each appearing 4-fid.	Croton heptalon
20	Pistillate sepals yellowish woolly-tomentose; styles each 2 times 2-fid.	Croton lindheimeri
10	Shrubs or perennial herbs.	> 21
21	Staminate petals 0; columella 3-winged.	> 22
22	Plants monoecious or sometimes apparently dioecious; leaf blades much less than 2 times as long as wide, petioles 1/2 to equal blade length; beaches and coastal dunes, Atlantic and Gulf coasts.	Croton punctatus
22	Plants strictly dioecious; leaf blades more than 2 times as long as wide, petioles usually less than 1/2 blade length; dunes and sandy areas, inland as well as coastal, Arizona, California, Nevada, Utah.	> 23
23	Pedicels of pistillate flowers to 1 mm, 1–3 mm in fruit; seeds 4–5.5 × 3.5–5.5 mm; various habitats, Arizona, California, Nevada, Utah.	Croton californicus
23	Pedicels of pistillate flowers 1–2 mm, 4–7 mm in fruit; seeds 6.5–7 × 2–3 mm; dunes of se-most California and sw Arizona.	Croton wigginsii
21	Staminate petals (4–)5(–6); columella apex with 3 rounded, inflated lobes or 3 sharp projections.	> 24
24	Perennial herbs; columella apex with 3 sharp projections.	Croton pottsii
24	Shrubs; columella apex with 3 rounded, inflated lobes.	> 25
25	Petioles mostly 1/4–7/10+ leaf blade length, if shorter (C. fruticulosus) then leaf blade margins finely serrulate and staminate sepals 0.8–1.2 mm; leaf blades usually ovate to lanceolate or oblong, margins entire, minutely glandular-denticulate, or serrulate, abaxial surfaces stellate-hairy or glabrous; staminate petal abaxial surfaces glabrous except margins often villous or ciliate; seeds shiny; styles 2- or 4-fid, terminal segments 6 or 12.	> 26
26	Styles 2-fid, terminal segments 6; petioles mostly 1/8–1/2 leaf blade length; stamens 9–16; stipules not glandular-ciliate; petioles not stipitate-glandular at apices (C. sonorae glandular-ciliate on leaf blade margins).	> 27
27	Staminate pedicels 2.5–4 mm, pistillate 0–0.5 mm; seeds 4–5 mm; leaf blades 2–8 cm, adaxial surfaces puberulent, margins serrulate, often slightly undulate.	Croton fruticulosus
27	Staminate pedicels 1–1.5 mm, pistillate 1–4 mm; seeds 6–7 mm; leaf blades 0.8–4 cm, adaxial surfaces glabrate, margins entire, not undulate.	Croton sonorae
26	Styles 4-fid, terminal segments 12; petioles 3/8–7/10+ leaf blade length; stamens 15–35; stipules glandular-ciliate or not; petioles stipitate-glandular or without glands at apices.	> 28
28	Stipules and leaf blade margins glandular-ciliate; petioles stipitate-glandular at apices.	Croton ciliatoglandulifer
28	Stipules not glandular-ciliate (may be small clusters of stipitate glands or have short-stipitate glandular processes); leaf blade margins not glandular-ciliate (sometimes glandular-denticulate or with glandular-capitate processes); petioles without glands at apices.	> 29
29	Leaf blade abaxial surfaces densely stellate-hairy; staminate sepals 3–4 mm, petals 3–4 mm; pistillate sepals 4 mm, petals 1 mm; seeds 3–4 × 2.5–3 mm.	Croton humilis
29	Leaf blade abaxial surfaces glabrous or sparsely stellate-hairy (usually along margins); staminate sepals 0.8–1 mm, petals 1–1.3 mm; pistillate sepals 5–6 mm, petals 0 or 2.5–3.5 mm; seeds 4–5 × 3–4 mm.	Croton soliman
25	Petioles mostly 1/10–1/4 leaf blade length, if longer (C. incanus) then leaf blade surfaces stellate-tomentose, staminate petal abaxial surfaces villous, and seeds dull; leaf blades usually obovate, elliptic, oblong, or linear, sometimes lanceolate or ovate, margins entire or minutely denticulate, abaxial surfaces stellate-hispid, stellate-tomentose, or stellate-hairy; staminate sepals 1.5–2.5 mm; staminate petal abaxial surfaces villous, glabrate, or glabrous except base sometimes villous and margins ciliate or tomentose; seeds shiny or dull; styles 2-fid, terminal segments 6.	> 30
30	Leaf blade adaxial surfaces glabrous or minutely stellate-puberulent; plants dioecious.	> 31
31	Leaf blades narrowly obovate, oblong, elliptic, or lanceolate, mostly less than 3.5 times as long as wide, petioles 1–1.5 cm; Texas.	Croton cortesianus
31	Leaf blades linear to narrowly oblong, mostly more than 4 times as long as wide, petioles 0.3–1 cm; se Florida.	Croton linearis
30	Leaf blade adaxial surfaces stellate-tomentose or stellate-hairy; plants monoecious or dioecious.	> 32
32	Shrubs 10–20 dm, much-branched distally; stipules linear-subulate, 2–3 mm; stems stellate-velutinous.	Croton incanus
32	Shrubs 1–5 dm, much-branched proximally; stipules papilliform, 0.1–0.5 mm; stems coarsely stellate-tomentose.	> 33
33	Plants dioecious; stipules each 1 glandular papilla, 0.1 mm; capsules 5.5–6 mm wide; seeds 3.6–4.7 mm.	Croton sancti-lazari
33	Plants monoecious; stipules each 5–10 glandular papillae, 0.2–0.5 mm; capsules 6–8 mm wide; seeds 5.5–7 mm.	Croton suaveolens