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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; corollas 2.5-4 mm long
..2 Stigmas conic, ellipsoid, globose, obovoid, ovoid, or cuboid; corollas 3-7 mm long.
....3 Corollas 4-7 mm long; stigmas cuboid
1 Styles separate and distinct from the base; capsule not circumscissile (except the rare exotics C. epilinum and C. epithymum).
......4 Stigmas elongated, terete or conical; capsule circumscissile; [subgenus {or genus} Cuscuta].
........5 Style about equaling the ovary, included in the corolla; fruit 2.0-2.5 mm long
........5 Style (including the stigma) much longer than the ovary, exserted from the corolla; fruit ca. 1.5 mm long
......4 Stigmas capitate, about as wide as long; capsule not circumscissile, either indehiscent or rupturing irregularly; [subgenus {or genus} Grammica].
..........6 Each flower subtended by 1-10 imbricate bracts; sepals distinct nearly to the base.
............ ..8 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
............ ..8 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
..........6 Flowers not bracteate (rarely a single bract may be present towards the base of the pedicel); sepals various.
............ ....9 Perianth surface granular (papillate); fresh flowers fleshy; corolla lobes acute, tips typically curved inward.
............ ......10 Corolla tubular; calyx > ½ as long as the corolla; flowers 4 (-5)-merous; infrastaminal scales reduced, merely bifid or shallowly toothed
............ ........11 Calyces shorter than the corolla tubes, divided 1/3-1/2 of the lengths; calyx lobes triangular-ovate, bases overlapping
............ ........11 Calyces longer than the corolla tubes, divided 2/3 of the lengths; calyx lobes lanceolate, the lobes not overlapping.
............ ..........12 Flower clusters dense; calyx lobes acute-attenuate; hosts usually Iva annua, more rarely Symphyotrichum
............ ..........12 Flower clusters loose; calyx lobe apices acute; hosts herbs and woody plants (including Iva annua)
............ ....9 Perianth surface not granular; fresh flowers not especially fleshy; corolla lobes various.
............ ............ 13 Stylopodium (a thickened ridge at the base of the style) present; flowers 5-merous.
............ ............ ..14 Ovary with a long (1-1.5 mm), beak-like projection at the top; corolla 4-6 mm long, 4-6 mm wide; seeds 2-3 mm long; [of the Mountains]
............ ............ ..14 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].
............ ............ ....15 Flowers 2.3-3.1 mm long; calyx ca. as long as the corolla tube or slightly shorter, lobes oblong-ovate, not overlapping basally; corolla 2.2-2.7 (-3) mm long, tube 0.8-1.5 (-2) mm long, broadly campanulate to cupulate; infrastaminal scales longer than the corolla tube; capsules surrounded by the withered corolla in the lower 1/2
............ ............ ....15 Flowers 3-4.5 mm long; calyx ca. reaching the middle of the corolla tube, lobes ovate to suborbicular, basally overlapping; corolla 3-4.4 mm long, tube (1.7-) 2-2.5 (-2.8) mm long, campanulate, infrastaminal scales shorter than the corolla tube to nearly reaching filament bases; capsules 3/4 surrounded by the withered corolla or capped in the distal 1/2 by it.
............ ............ ......16 Infrastaminal scales ca. reaching filament bases (rarely shorter), apex rounded; styles (0.6-) 1.1-2.5 mm long
............ ............ ........17 Corolla tube 1.4-2.5 mm long, withered corolla loosely surrounding the capsule before falling
............ ............ ..........18 Flowers subsessile, therefore in globular inflorescences.
............ ............ ..........18 Flowers on pedicels slightly shorter than to longer than the flowers, therefore in loose inflorescences.
............ ............ ............ ....21 Flowers mostly as wide as long.
............ ............ ............ ......22 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
............ ............ ............ ......22 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.
............ ............ ............ ........23 Flowers 4-merous; flowers 0.9-1.4 mm long; stems very slender; [on granite and sandstone outcrops]
............ ............ ............ ........23 Flowers 5-merous; flowers 1.5-2.5 mm long; stems not especially slender; [widespread]
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