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Key to Iva

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1 Plants perennial, fleshy, glabrous (or strigillose on the leaf faces); [mostly of maritime situations, such as brackish marshes, marsh edges, or ocean dunes]; [section Iva].
..2 Outer phyllaries united; [rare waif of disturbed areas and beaches]
..2 Outer phyllaries distinct; [collectively common and widespread natives of the outer Coastal Plain].
....3 Leaves 1.5-4.5 (-6.0) cm long, 0.4-1.0 (-1.5) cm wide, 1-3 mm thick when fresh, mostly untoothed; involucres 4-7 mm high; leaves opposite below, alternate from midstem upward; [mostly of dunes and the upper beach]
....3 Leaves 4-10 cm long, 0.7-4.0 cm wide, 0.5-1 mm thick when fresh, usually toothed; involucres 2-4 mm high; leaves opposite (alternate only in or just below the inflorescence); [mostly of marshes, marsh edges, and wet hammocks].
......4 Larger leaves 4-7 (-8.5) cm long, 0.7-1.5 (-2.1) cm wide, 4-10× as long as wide, subentire or with 1-8 (rarely more) teeth on each side; [of NJ southward]
......4 Larger leaves 6-10 cm long, 2.0-4.0 cm wide, 1.5-4× as long as wide, usually with 8-17 teeth on each side; [of n. NC northward]
1 Plants annual (perennial in I. asperifolia) , not fleshy, more-or-less pubescent (at least in the inflorescence); [of mainly inland wetlands or disturbed areas].
........5 Leaves 20-70 mm wide, ovate; staminate flowers usually 8-16 (-20) per head; [mostly of disturbed ground]; [section Iva]
........5 Leaves 0.5-8 mm wide, linear; staminate flowers 1-9 per head; [section Linearbractea].
..........6 Involucres 1.5-2 mm high; outer phyllaries distinct, glandular-punctate; leaves 0.5-3 mm wide; pistillate flowers 3 per head
..........6 Involucres 2.5-3 mm high; outer phyllaries connate, not glandular-punctate; leaves 1-8 mm wide; pistillate flowers 1 (-2) per head
............ 7 Plants annuals, erect, 5-12 dm tall; staminate flowers 1-5 per head
............ 7 Plants perennials, decumbent, rooting at the nodes, 2-5 dm tall; staminate flowers 3-9 per head
............ ..8 Stems decumbent, rooting at the nodes; leaves mostly oblong- lanceolate; involucres without markedly spreading, broad-based hairs; [Panhandle FL; coastal Tamaulipas and Veracruz, Mexico]
............ ..8 Stems stiffly erect, only rarely rooting at the nodes; leaves mostly lanceolate; involucres with markedly broad-based spreading hairs, rarely not; [n. coastal Tamaulipas, Mexico, and s. Texas]
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