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Project Name Data (Last Modified On 6/4/2013)
 

Flora Data (Last Modified On 6/4/2013)
Genus Ageratum L.
PlaceOfPublication Sp. P1. 2: 839. 1753.
Note TYPE: A. conyzoides L.
Synonym Carelia G. Pontedera ex P. C. Fabricius, Enum. 85. 1759. TYPE: A. conyzoides L.
Description Annual herbs to perennial subshrubs, with few to many branches, the base often decumbent with numerous adventitious roots. Leaves opposite or alternate, petiolate; blades elliptical or lanceolate to deltoid or ovate, the margins entire to dentate or shallowly lobed, the undersurface usually with obvious sessile or sunken glandular-punctations, usually trinervate from the base. Inflorescence cymose to subcorymbose, sometimes subumbellate. Heads discoid with 20-125 florets; involucral bracts 30-40, eximbricate, equal or subequal, in 2-3 series, lanceolate, coriaceous; receptacle conical, glabrous or paleaceous; corolla funnelform or with distinct basal tube, the lobes 5, about as long as wide, papillose on inner surface, sometimes hispidulous on outer surface, the cells of the limb elongate with sinuous walls; anther collars slender, the walls of the cells with distinct annular thickenings, the anther appendage large, longer than wide; style base without enlarged node, glabrous, the style appendages linear, usually strongly and densely papillose. Achenes 4-5-ribbed, glabrous or with short bristles on the ribs; carpopodium distinct, large, usually asymmetrical; pappus lacking or coroniform or of 5-6 free flattened sometimes awn-like scales. Pollen with short spines.
Habit herbs subshrubs
Distribution The genus Ageratum contains 43 species and ranges from Mexico and Central America to the West Indies and South America.
Note Two species, A. conyzoides and A. houstonianum, are widely adventive in warmer parts of the Old World. Six species have been collected in Panama.
Reference Grierson, A. J. C. 1972. Critical notes on the Compositae of Ceylon. Ceylon Jour. Sci., Biol. Sci. 10: 42-60. Johnson, M. F. 1971. A monograph of the genus Ageratum L. (Compositae- Eupatorieae). Ann. Missouri Bot. Gard. 58: 6-88. King, R. M. & H. Robinson. 1972. Studies in the Eupatorieae (Asteraceae). LXXXVII. Additions to the genus, Ageratum. Phytologia 24: 112-117. Robinson, B. L. 1913. II. Revisions of Alomia, Ageratum and Oxylobus. Contr. Gray Herb. 42: 438-491.
Key a. Stems puberulous to hirtellous with short hairs, often becoming glabrous; petioles usually 2-5 mm long. b. Leaf blades narrowly elliptical to narrowly lanceolate, with narrowly cuneate bases ...... 1. A. chiriquense bb. Leaf blades ovate to ovate-lanceolate, with rounded to shortly cuneate bases ...... 6. A. panamense aa. Stems sparsely to densely pilose with long hairs; petioles usually 10-30 mm long. c. Involucral bracts without scarious or irregular margins, glabrous; achenes glabrous ...... 5. A. oliveri cc. Involucral bracts with scarious and often toothed margins, with few to many hairs on outer surface; achenes often scabrid or with short bristles on the ribs. d. Pappus lacking ...... 4. A. microcarpum dd. Pappus of larger scales or awns. e. Corolla less than 2 mm long, not as long as the awned pappus scales; style branches very slender with papillae forming nearly 1/2 the width ...... 2. A. conyzoides ee. Corolla over 2 mm long, as long as or longer than the awned pappus scales; style branches slightly broader distally, with small pointed papillae forming less than '/4 the width ...... 3. A. houstonianum
 
 
 
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