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Project Name Data (Last Modified On 6/18/2013)
 

Flora Data (Last Modified On 6/18/2013)
Genus Tridax L.
PlaceOfPublication Sp. PL 2: 900. 1753
Note TYPE: T. procumbens L.
Synonym Bartolina Adanson, Fam. 2: 124. 1763, nom. invalid. Amellus Ortega ex Willd., Sp. P1. 3: 2214. 1803, pro syn. Balbisia Willd., Sp. P1. 3: 2214. 1803, nom. rejic., Balbisia Cav. 1804, nom. cons. TYPE,: B. elongata Willd. Sogalgina Cass., Bull. Soc. Philom. 31. 1818. TYPE: Galinsoga trilobata Cav. Galinsogea H.B.K., Nov. Gen. Sp. Pl. 4: 252, tab. 386. 1818. TYPE: G. trilobata Cav. Ptilostephium H.B.K., Nov. Gen. Sp. Pl. 4: 253, tab. 387-388. 1818. LECTOTYPE: P. coronopi- folium H.B.K. (here chosen). Carphostephium Cass., Dict. Sci. Nat. 44: 62. 1826. TYPE: Ptilostephium trifidum H.B.K. Mandonia Wedd., Bull. Soc. Bot. France 11: 50, pl. 1. 1864. TYPE: M. boliviensis Wedd.
Description Annual or perennial herbs with slender taproots; stems procumbent, decumbent or erect, subscapose to leafy, sparsely to densely pubescent. Leaves opposite, or rarely alternate above, petiolate or sessile, simple, trilobed, pinnately lobed or divided, the margins entire, serrate, dentate to repand. Inflorescences with heads solitary or in few- to many-headed cymose panicles; peduncles slender to stout, elongate, pubescent, often with glandular-tipped trichomes. Heads discoid or radiate, campanulate (urceolate in T. erecta); involucral bracts 2-3-seriate and subequal in length to 4-5-seriate and obviously unequal in length, imbricate, greenish, often purplish at the apex, the inner bracts with scarious, purple margins; receptacle conical to convex or flattened; paleas scarious, persistent, rarely readily deciduous, partially enclosing the disc achenes, yellowish to yellow-green; ray florets fertile if present, the ligules white, yellow, roseate, or purple, obscurely to conspicuously bilabiate, the external lip with 2-4 shallow to deep lobes, the inner lobelets obvious to rudimentary, or wanting, the tube narrow, often pubescent; disc florets regular (except in T. bilabiata and occasionally in T. coronopifolia of Mexico), yellow, greenish-yellow, purplish, or whitish, the limb tubular or narrowly funnelform, glabrous or pubescent, the lobes 5, equal, sublanceolate, acute or obtuse, erect or reflexed, the anthers somewhat to nearly completely exserted, the appendages ovate, cordate, sagittate, or rhombic, the base sagittate, the style branches recurved to revolute, slender, subterete to flattened on the inner surfaces, with subulate tips. Achenes turbinate, narrowly obconic to sub- cylindric, terete to ridged, glabrous to densely pubescent with ascending hairs, pappus usually of ca. 20 plumose bristles or fimbriate, linear-lanceolate scales, rarely absent. Chromosome number x = 9, 10
Habit herbs
Distribution Tridax is a genus of 27 species occurring in Mexico, Central America, and South America with the greatest number of species found in Mexico.
Note It is distinguished from other members of the subtribe Galinsoginae by its generally bilabiate ray corollas (although this character also occurs occasionally in some Galinsoga), the long disc corollas, and chromosome numbers based on 9 and 10.
Reference Powell, A. M. 1965. Taxonomy of Tridax (Compositae). Brittonia 17: 47-96.
 
 
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