Flora of the Southeastern United States
2022 Edition

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Key to Croton

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1 Plant an evergreen shrub, (1-) 2-3 m tall; pistillate flowers with well-developed, pale green petals; styles 3, unbranched (rarely 2-branched), the terminal segments therefore 3 (or 6); [subgenus Quadrilobi; section Alabamenses]
..2 Lower surface of leaf blade silvery, the scales mostly unpigmented or light amber (a few dark blackish brown scales sometimes present); leaf blades narrowly ovate, 2-3× as long as wide, broadest at or slightly below the midpoint, cuneate to rounded at the base; inflorescences 9-18-flowered, producing 0-11 fruits; [AL]
..2 Lower surface of leaf blades coppery, some of the scales unpigmented, others with dark reddish brown center and reddish amber rays; leaf blades narrowly ovate, 1.5-2.5× as long as wide, broadest well below the middle, subcordate, truncate, or broadly ovate at the base; inflorescences 6-14-flowered, producing 0-6 fruits; [TX]
1 Plant an annual or perennial herb or shrub, 0.1-2 m tall; pistillate flowers lacking petals (or sometimes with small, linear, and whitish petals in C. linearis); styles 2 or 3, 2-branched or several-branched, the terminal segments therefore 4, 6, or more; [subgenus Geiseleria].
....3 Leaves with coarsely serrate or crenate margins; 1-2 cup-shaped glands present near the junction of the petiole and the leaf blade; [subgenus Geiseleria; section Geiseleria].
......4 Leaf blades glabrous, or nearly glabrous with fewer than 2 stellate hairs on lower surface 0.6-2.0 cm long; cup-shaped glands 0.1-0.5mm wide; stem brown and woody; clumping structure; [FL]
......4 Leaf blades greater than 1cm long, sparsely to densely covered with stellate trichomes; stem pale.
........5 Central trichomes on the lower surface of the leaf ≥ 1 mm, densely pubescent (5-13 hairs per mm2); leaf blades 1-3 cm long; cup-shaped glands 0.5-1 mm wide; [TX]
........5 Central trichomes on the lower surface of the leaf ≤1mm, or not as described above.
..........6 Leaf blades densely pubescent (7-15 hairs per mm2); leaves 0.8-4 cm long, 2-6x as long as wide, often silvery in appearance; cup-shaped glands 0.1-0.8 mm wide; [TX]
..........6 Leaf blades densely to sparsely pubescent or not as described above; [collectively widespread].
............7 Tops of leaves densely pubescent (3-12 hairs per mm2); leaves 1.0-3 cm long, ca. 1.5-2× as long as wide; cup-shaped glands 0.3-0.6 mm wide; branching pattern clumped; [s. FL]
............7 Upper leaf surface not as densely pubescent (0-7 hairs per mm2); upper leaves 1-6 cm long, 2-6x as long as wide; cup-shaped glands 0.1-0.8 mm wide; pale stem; branching from one main central branch; widespread
....3 Leaves with entire margins; glands absent at the junction of the petiole and the leaf blade.
..............8 Lower leaf surface densely lepidote or stellate-lepidote, silvery.
................9 Inflorescences unisexual (rarely bisexual); staminate petals 0; leaf blades 1-1.4× as long as wide; petioles 10-40 mm long; plant a fleshy shrub; [of coastal dunes]; [subgenus Geiseleria; section Drepadenium]
................9 Inflorescences bisexual; staminate petals 5; leaf blades 2-20× as long as wide; petioles 1-10 (-20) mm long; plants annual or perennial herbs.
..................10 Petioles 2-10 (-20) mm long, at least some of them > 1/3 al long as the leaf blades; fruit 3-locular, dehiscent; seeds 3 per fruit, 2.5-5 mm long; petals of the staminate flowers lepidote; [of dry longleaf pinelands]; [subgenus Geiseleria; section Argyranthemi]
..................10 Petioles 1-5 mm long, < 1/5 the length as the leaf blades; fruit 1-locular, indehiscent; seed 1 per fruit, 2-2.5 mm long; petals of the staminate flowers glabrous on the surfaces, villous on the margins; [subgenus Geiseleria; section Crotonopsis].
....................11 Inflorescences 1-4 cm long, with 3-6 pistillate flowers arranged loosely toward the base; staminate flowers usually > 1 mm in diameter; stellate-lepidote trichomes of the fruit numerous, with radii much longer than the fused portion and often ascending (giving the fruit a fuzzy appearance when viewed under magnification); stellate trichomes of the upper leaf surface sparse, the radii not overlapping the radii of nearby stellae, the radii 5-8 per trichome; leaves 1-3 mm wide
....................11 Inflorescences usually < 1 cm long, with 1-2 pistillate flowers crowded at the base (appearing sessile in the axil of the subtending leaf); staminate flowers usually < 1 mm in diameter; stellate-lepidote trichomes of the fruit sparse, with radii fused for all or most of their lengths, appressed; stellate trichomes of the upper leaf surface denser, the radii usually overlapping the radii of nearby stellae, the radii often only 1-3 per trichome (as viewed near the midvein); leaves 1.5-4 (-15) mm wide
..............8 Lower leaf surface stellate-pubescent, not silvery.
......................12 Plant a shrub; [of s. FL or s. TX]; [subgenus Adenophylli; section Adenophylli].
........................13 Leaf blades 4-10× as long as wide, linear (or lanceolate); leaf blades thick; leaf margins entire; petioles with paired glands at junction with leaf blade; dioecious shrub to 20 dm tall
........................13 Leaf blades 1.5-3× as long as wide, ovate; leaf blades thin in texture; leaf blades entire or more usually glandular-denticulate; petioles lacking paired glands at junction with leaf blade; monoecious shrubs to 8 dm tall
..........................14 Staminate flowers with 30-35 stamens
..........................14 Staminate flowers with 15-20 stamens
......................12 Plant an annual herb; [collectively widespread].
............................15 Plants dioecious, the inflorescences therefore unisexual; staminate flowers lacking petals; capsules verrucose; [subgenus Geiseleria; section Drepadenium].
..............................16 Plants 5-15 dm tall; lower leaf surfaces densely stellate-tomentose; capsules 8-9 mm long; [s. TX, mainly along the coast, from Calhoun County southwards]
..............................16 Plants 2-9 dm tall; lower leaf surfaces densely appressed stellate; capsules 5-8 mm long; [widespread in TX, also scattered eastwards as an adventive]
............................15 Plants monoecious, the inflorescences either bisexual or unisexual; staminate flowers with 3-5 petals; capsules smooth; [subgenus Geiseleria; section Heptallon].
................................17 Lower leaf surfaces appearing brown-dotted, because some of the stellate hairs have dark brown centers; terminal style segments 4; ovaries 2-locular, only 1 fertile
................................17 Lower leaf surfaces not brown-dotted (none of the stellate hairs with brown centers); terminal style segments 6-18 (-24); ovaries 3 locular, all 3 usually fertile.
..................................18 Pistillate flowers with 5-6 sepals; terminal style segments 6; herbs 1-5 dm tall
..................................18 Pistillate flowers with 6-9 sepals; terminal style segments 12-18 (-24); herbs 3-20 dm tall
....................................19 Staminate flowers with sepals and petals 0.8-1.0 mm long; styles 2-3 mm long.
......................................20 Leaves (the larger) 4-15 cm long, 1.5-6 cm wide (generally 2-3× as long as wide), lanceolate to elliptic, cordate at the base; hairs of 2 colors, the shorter gray, the longer tan; lobes of the calyx of the pistillate flowers (6-) 7-9 (-12); [alien, of disturbed habitats]
......................................20 Leaves (the larger) 2.5-6 cm long, 0.7-1.5 cm wide (generally 3-6× as long as wide), linear to linear-lanceolate, cuneate at the base; hairs of 1 color, all gray; lobes of the calyx of the pistillate flowers 5-6; [native, of Coastal Plain pondshores]
....................................19 Staminate flowers with sepals and petals 1.0-2.0 mm long; styles 3-4 mm long.
........................................21 Pistillate flowers with sepals whitish appressed-tomentose; styles 3, terminal segments 12, with each style branching once into 4 segments
........................................21 Pistillate flowers with sepals yellowish woolly-tomentose; styles 3, terminal segments 12, with each style branching into 2, and then branching again to make 4 segments