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(Last Modified On 6/18/2013)
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(Last Modified On 6/18/2013)
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Genus
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Cosmos Cav.
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PlaceOfPublication
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Icon. Descr. P1. 1: 9. 1791.
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Note
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TYPE: C. bipinnatus Cav.
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Synonym
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Cosmea Willd., Sp. PI., ed. 4. 3: 2250. 1803, orth. mut. Cosmos Cav. Cosmus Pers., Syn. PI. 2: 477. 1807, orth. mut. Cosmos Cav. Adenolepsis Less., Linnaea 6: 510. 1831. TYPE: A. pulchella Less.
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Description
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Herbs or rarely subshrubs, perennial or annual, mostly glabrate, sometimes hispid; stems branched, erect, slender, quadrate or terete; roots of perennial species thickened, fasciculate. Leaves opposite, mostly compound or dissected, petiolate. Inflorescence a solitary head or loose aggregate of heads; peduncles elongate, terete or slightly angled; bracts resembling the leaves, one or two bracteoles sometimes alternate along the peduncle. Head normally radiate, sometimes showy; involucral bracts in 2 dissimilar series each about as many as the ray florets, the outermost herbaceous, drying striate, basally fused into a meniscoid hypanthium, the innermost longer, broader, membranous, mostly not striate, sometimes colored like the rays; receptacle nearly flat; paleas scarious-membranous, flat or cuculate, curved around the ovary; ray florets 5-12 in 1 series (except some horticulture forms), the corolla variously colored, the limb 3-denticulate, longitudinally sulcate with scattered elongate slender hairs on the dorsal surface, the ventral surface minutely puberulent-papillose near the base, the tube short, dorsiventrally com- pressed, the ovary rudimentary; disc florets few-many, often forming a cone or cylindrical disc, colored like the rays or not, the corolla cylindrical or narrowly obconical, the limb not demarcated from the tube, faintly 5-angled, glabrate, 5-lobed, the lobes obtuse, ciliate or ventrally pubescent, the point of filament insertion marked by a ridge on the corolla tube, the anthers with large appendages, basally obtuse or subauriculate, the filaments pubescent, the style branches pilose, truncate with a short or long acicular appendage, often appearing acicular overall, the ovary subeylindrical, with the basal half slightly enlarged, sometimes strigose. Achenes narrowly cylindrical-fusiform, often apically narrowed into a slender beak, sometimes strigose, mostly with 1-3 stout, barbed awns.
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Habit
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Herbs or rarely subshrubs
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Distribution
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Cosmos includes about 30 species occurring mainly in Mexico but ranging south into Central America.
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Note
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It is closely related to Dahlia, Coreopsis, and Bidens. Dahlia is distinguished by its naked awns and more robust habit. Coreopsis does not have thickened rootstocks and the awns are not barbed. In Bidens the achene apex is not produced into a distinct beak. Three easily distinguished species of Cosmos occur in Panama. One of these, C. sulphureus is known mainly from cultivation. Cosmos bipinnatus Cav., native of Mexico and Arizona, is frequently cultivated for ornament in other countries and may be expected in Panamanian gardens from imported seed. It resembles C. crithmifolius but is annual instead of perennial, and the similar leaves are shorter and softly flexuous instead of stiffly erect. Cosmos bipinnatus is available from northern seed houses in various colors.
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Key
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a. Leaf segments stiff, uniform in width ( 1-2 mm); perennial; rays showy pink; bristles at summit of achene 1-5 and erect ...... 2. C. crithmifolius aa. Leaf segments membranaceous, flexuous, conspicuously wider (to 6 mm) near the middle; annual; rays various colors; bristles at summit of achene 0-3, divaricate, seldom erect. b. Flowers showy yellow; anthers yellow; inner involucral bracts mostly orange or yellowish at the tips; cultivated species sometimes escaping ...... 3. C. sulphureus bb. Flowers pink or purplish (?or white), mostly not showy; anthers black; inner involucral bracts mostly not colored; native species ...... 1. C. caudatus
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