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Published In: Species Plantarum 2: 1004. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
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Project Data     (Last Modified On 7/23/2009)

 

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3. Croton L. (croton)

Plants annual (perennial herbs, shrubs, or trees elsewhere), monoecious or dioecious (in C. texensis), taprooted, with the sap clear (somewhat colored but not milky elsewhere), pubescent with branched or stellate hairs, these sometimes with branches more or less fused and then appearing as minute, scurfy, peltate scales; stinging hairs absent. Stems usually solitary, erect or ascending, unbranched or more commonly branched, sometimes from near the base. Leaves alternate but sometimes appearing opposite or whorled because of stem portions with very short internodes, sessile to long-petiolate, the petiole sometimes with 1 or 2 large, saucer-shaped glands at the tip, attached at the base of the nonpeltate blade. Leaf blades linear to nearly circular, tapered, angled, or rounded at the base, rounded or angled to tapered to a bluntly or sharply pointed tip, the margins entire or nearly so (regularly toothed in C. glandulosus), usually pinnately veined (sometimes only the midvein apparent). Stipules absent (in C. michauxii and C. willdenowii) or usually not apparent at flowering, then either minute (less than 1 mm long), lanceolate to ovate, tan scales that are shed early or small glandular dots that are obscured by the pubescence. Inflorescences terminal, axillary, and/or from the stem branch points, appearing as short, dense, spikelike racemes or dense clusters, the staminate and pistillate flowers variously positioned, each flower usually with an inconspicuous, short, slender bract (often threadlike, brown, and shed before flowering). Flowers with a nectar disc, this entire or with lobes equal to the number of calyx lobes. Staminate flowers with the calyces usually deeply 5-lobed, corollas of 5 petals (except in C. texensis) about as long as the calyx, the 5–20 small stamens (more elsewhere) with the filaments free. Pistillate flowers with the calyces usually deeply 5–12-lobed, corollas highly reduced or absent, the ovary with 1–3 locule(s) and 1 ovule per locule, the 1–3 style(s) free (or in some 3-styled species fused at the very base), each deeply 2-lobed, the lobes sometimes lobed again or branched. Fruits unlobed or slightly 3-lobed (circular in cross-section or nearly so), dehiscent except in C. michauxii and C. willdenowii. Seeds nearly spherical to oblong-ovoid or ovoid, the caruncle absent or a small, light-colored knob at the end adjacent to the attachment point, the surface smooth and often shiny, yellowish brown or reddish brown to dark brown, sometimes mottled. More than 800 species, nearly worldwide, but most diverse in tropical and subtropical regions.

The taxonomy and phylogeny of this large and morphologically variable genus still requires much further study. As noted by Webster (1967), for its size Croton contains surprisingly few species of economic importance. The common houseplants with brightly colored variegated leaves referred to as croton actually are Codiaeum variegatum (L.) A. Juss., a paleotropical member of the family not particularly closely related to the true crotons. The seeds of the Asian Croton tiglium L. are the source of croton oil, which has uses similar to those of castor oil (see the treatment of Ricinus). The stellate hairs sometimes are shed easily when plants are handled and can cause eye irritation.

 

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1.1. Leaf blades with the margins finely toothed; petioles with 1 or 2 large, saucer-shaped glands at the tip ... 2. C. GLANDULOSUS

Croton glandulosus
2.1. Leaf blades with the margins occasionally slightly wavy toward the base but otherwise entire; petioles lacking glands at the tip

3.2. Plants dioecious; staminate flowers lacking a corolla; pistillate flowers with the 3 styles each divided nearly to the base into 46 lobes ... 6. C. TEXENSIS

Croton texensis
4.2. Plants monoecious; staminate flowers with a corolla; pistillate flowers with the 13 styles each 1 time deeply divided (2 or 3 times divided in C. capitatus but with the second and third order divisions usually well above the base)

5.3. Ovary 3-locular; styles 3, each deeply 2-lobed, the lobes sometimes lobed again; fruits 3-seeded (rarely 2-seeded by abortion of 1 ovule)

6.4. Pistillate flowers with the calyx 69-lobed; styles each lobed 2 or 3 times (the total number of stigmatic branches thus theoretically 1224 per flower, but in practice mostly 1216); fruits 69 mm in diameter ... 1. C. CAPITATUS

Croton capitatus
7.4. Pistillate flowers with the calyx 5-lobed; styles each deeply lobed only 1 time (the total number of stigmatic branches thus 6 per flower); fruits 45 mm in diameter ... 3. C. LINDHEIMERIANUS

Croton lindheimerianus
8.3. Ovary 1- or 2-locular; styles 2 or 3, each shallowly or deeply 2-lobed; fruits usually 1-seeded

9.5. Ovary 2-locular (1 of the locules usually aborting and the dehiscent fruit thus usually 1-seeded); styles 2, each deeply 2-lobed; seeds with a knoblike caruncle; leaf blades with the undersurface pubescent with stellate hairs (the calyx and ovary also with stellate hairs) ... 5. C. MONANTHOGYNUS

Croton monanthogynus
10.5. Ovary 1-locular (the indehiscent fruit thus 1-seeded); styles 3, each shallowly 2-lobed toward the tip; seeds lacking a caruncle; leaf blades with the undersurface pubescent with peltate, scalelike trichomes (these also on the stem, calyx, and ovary)

11.6. Leaf blades with the upper surface pubescent with minute, nonoverlapping, stellate hairs, the more or less equal branches 0.20.3 mm long; stems, undersurface of the leaf blades, and especially fruits with peltate scales consisting of a relatively narrow, fused central disc with a relatively long fringe of slender, stellate extensions beyond the disc ... 4. C. MICHAUXII

Croton michauxii
12.6. Leaf blades with the upper surface pubescent with short, overlapping, stellate hairs, the often unequal branches 0.61.0 mm long; stems, undersurface of the leaf blades, and especially fruits with peltate scales consisting of a relatively broad, fused central disc with a relatively short fringe of slender, stellate extensions beyond the disc ... 7. C. WILLDENOWII
Croton willdenowii
 
 
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