Flora of the Southeastern United States
2022 Edition

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Key to Cuscuta

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1 Styles united for most of their length; capsule circumscissile; [subgenus {or genus} Monogynella].
..2 Stigmas flattened-depressed; flowers 2.5-4 mm long
..2 Stigmas oval or conical; flowers ca. 2 mm long
1 Styles separate and distinct from the base; capsule not circumscissile (except the rare aliens C. epilinum and C. epithymum).
....3 Stigmas elongated, terete or conical; capsule circumscissile; [subgenus {or genus} Cuscuta].
......4 Style about equaling the ovary, included in the corolla; fruit 2.0-2.5 mm long
......4 Style (including the stigma) much longer than the ovary, exserted from the corolla; fruit ca. 1.5 mm long
....3 Stigmas capitate, about as wide as long; capsule not circumscissile, either indehiscent or rupturing irregularly; [subgenus {or genus} Grammica].
........5 Each flower subtended by 1-10 imbricate bracts; sepals distinct nearly to the base.
..........6 Bracts lanceolate, the apices reflexed or spreading (squarrose)
..........6 Bracts ovate or orbicular, the apices erect, appressed and imbricate.
............7 Pedicels absent, the flowers in compact clusters sessile on the stem; bracts tightly subtending the flower, orbicular with rounded apices; styles not exserted in flower, and only 1.5-1.8 mm long in fruit; corolla lobes 0.9-1.1 mm long
............7 Pedicels 0.5-3 mm long, the flowers in loose panicles; bracts loosely subtending the flower, ovate with bluntly pointed apices; styles long-exserted, 2.5-3.5 mm long in flower and fruit; corolla lobes 1.8-2.0 mm long
........5 Flowers not bracteate (rarely a single bract may be present towards the base of the pedicel); sepals various.
..............8 Perianth surface granular (papillate); fresh flowers fleshy; corolla lobes acute, tips typically curved inward.
................9 Corolla tubular; calyx > ½ as long as the corolla; flowers 4 (-5)-merous; infrastaminal scales reduced, merely bifid or shallowly toothed
................9 Corolla campanulate; calyx ca. ½ as long as the corolla; flowers 5-merous; infrastaminal scales profusely fringed
..............8 Perianth surface not granular; fresh flowers not especially fleshy; corolla lobes various.
..................10 Stylopodium (a thickened ridge at the base of the style) present; flowers 5-merous.
....................11 Ovary blunt to pointed, but not beaked; corolla 2.2-3.5 mm long, 2-3 mm wide; seeds ca. 1.5 mm long; [widespread]
....................11 Ovary with a long, beak-like projection at the top; corolla 4-6 mm long, 4-6 mm wide; seeds 2-3 mm long; [of the Mountains]
..................10 Stylopodium absent; flowers 3-4-merous or 5-merous.
......................12 Flowers subsessile, therefore in globular inflorescences.
........................13 Flowers 5-merous
........................13 Flowers mostly 3-4-merous.
..........................14 Corolla lobes rounded or obtuse
..........................14 Corolla lobes acute
......................12 Flowers on pedicels slightly shorter than to longer than the flowers, therefore in loose inflorescences.
............................15 Flowers mostly longer than wide
............................15 Flowers mostly as wide as long.
..............................16 Flowers 1.5-3.0 mm long, at least some exceeding 2.5 mm long; calyx lobes not overlapping at the base in older flowers, and therefore the flowers not pronouncedly 5-angled
..............................16 Flowers 0.9-2.5 mm long; calyx lobes strongly overlapping and forming definite angles at the sinuses, thus the flower strongly 4-5-angled.
................................17 Flowers 4-merous; flowers 0.9-1.4 mm long; stems very slender; [on granite and sandstone outcrops]
................................17 Flowers 5-merous; flowers 1.5-2.5 mm long; stems not especially slender; [widespread]