Flora of the Southeastern United States
2022 Edition

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Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.

X
Keyed in multiple places:

Key to Asteraceae, Key B: herbaceous composites with opposite or whorled leaves
and discoid or disciform heads (lacking ray florets)

1 Pappus present, of 5-60 barbellate bristles; receptable naked (without paleae or well-developed bristles); [tribe Heliantheae; subtribe Eupatoriae].
..2 Plant a twining herb, phyllaries and disk florets 4 per head
..2 Plant stiffly erect to weakly spreading but never twining, phyllaries and disk florets usually > 4 per head.
....3 Leaves in whorls of 3-7, > 2 cm wide
....3 Leaves opposite, rarely alternate or whorled, if whorled, < 2 cm wide.
......4 Achenes (and ovaries) 8-10-ribbed; outer phyllaries longitudinally striate
......4 Achenes (and ovaries) (3-) 4-5-ribbed; outer phyllaries not noticeably longitudinally striate.
........5 Heads pink to blue.
..........6 Phyllaries in 4-6+ series, deciduous
..........6 Phyllaries in 2-4 series, persistent (or deciduous in Praxelis).
............ 7 Heads pink (rarely bluish); receptacles flat; florets 18-25 per head
............ 7 Heads blue; receptacles conic; florets 25-70 per head.
............ ..8 Bristles ca. 40; florets 25-30; phyllaries 15-25, unequal, deciduous (absence apparent in fruit)
............ ..8 Bristles ca. 30; florets 35-70+; phyllaries ca. 25, subequal, persistent
........5 Heads white to cream or, rarely, pale lilac.
............ ....9 Florets 3-7 per head
............ ....9 Florets at least 9 per head.
............ ......10 Phyllaries not strongly imbricate, with the principal ones subequal and sub-biseriate; petioles 0.5-10 cm
............ ......10 Phyllaries clearly imbricate, in 3+ series; some species epetiolate
1 Pappus absent, or of scales, setae, or awns; receptacle either naked, or with paleae or well-developed bristles.
............ ........11 Leaves whorled, linear, < 2 mm wide; head solitary; [aquatic herb growing in shallow stagnant water]
............ ........11 Leaves opposite (or alternate in part), broader in shape and > 5 mm wide; heads typically not solitary; [terrestrial or wetland plants].
............ ..........12 Receptacle naked.
............ ............ 13 Pappus of 4-10 scales; heads white, pink, or blue.
............ ............ ..14 Heads with 20-125 florets; leaves serrate; [rarely naturalized aliens in our area]
............ ............ ..14 Heads with 10-30 florets; leaves entire; [natives, of FL, s. GA, and MS in our area]
............ ............ 13 Pappus none, or of a few bristles or irregular coroniform lobes; heads green to yellow.
............ ............ ....15 Heads bright yellow, closely aggregated into corymbiform arrays of flat-topped to dome-shaped glomerules
............ ............ ....15 Heads greenish or greenish yellow, borne in spiciform, racemiform, or paniculiform arrays.
............ ............ ......16 Heads in paniculiform arrays, all or most of the heads not subtended by bracts
............ ............ ......16 Heads in spiciform or racemiform arrays, each 1 (-2) heads subtended by a bract
 Iva
............ ..........12 Receptable with paleae or well-developed bristles.
............ ............ ........17 Heads small, less than 1 cm in diameter at anthesis (the female heads enlarging in Xanthium); disc florets dull white or suffused with green or purple; florets mainly unisexual (either in the same heads and then males central and females peripheral, or in separate female and male heads); female florets 0-8 per head; [tribe Heliantheae; subtribe Ambrosiinae]
............ ............ ..........18 Heads unisexual; cypselas shed within an indurated bur or “nut” with hooked or straight spines developed from the phyllaries and/or paleae.
............ ............ ............ 19 Involucre of the female heads with tubercles or straight spines developing from the phyllaries; burs 1-8 mm long
............ ............ ............ 19 Involucre of the female heads with hooked spines developing from the phyllaries/paleae; burs 10-35 mm long
............ ............ ..........18 Heads bisexual, with functionally male and female flowers in the same head; cypselas shed individually, not enclosed.
............ ............ ............ ..20 Heads in paniculiform arrays, all or most of the heads not subtended by bracts
............ ............ ............ ..20 Heads in spiciform or racemiform arrays, each 1 (-2) heads subtended by a bract
 Iva
............ ............ ........17 Heads larger, mostly > 1 cm in diameter at anthesis; disc florets conspicuously white, yellow, pale yellow, or purple; florets mainly bisexual; female florets > 12 per head (except 2-8 in Polymnia).
............ ............ ............ ....21 Disc flowers maroon-purple; leaves mainly basal
............ ............ ............ ....21 Disc flowers white, pale yellow, or bright yellow; leaves mainly or strictly cauline.
............ ............ ............ ......22 Disc flowers bright yellow.
............ ............ ............ ........23 Involucre of phyllaries not subtended by a calyculus
............ ............ ............ ........23 Involucre of phyllaries subtended by a calyculus of bracts obviously different in color, texture, and shape than the phyllaries
............ ............ ............ ......22 Disc flowers bright white or pale yellow.
............ ............ ............ ..........24 Disc flowers bright white; leaves unlobed or with 2 basal lobes
............ ............ ............ ..........24 Disc flowers creamy or pale yellow; leaves prominently pinnately lobed, with 5-many lobes