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(Last Modified On 6/14/2013)
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(Last Modified On 6/14/2013)
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Genus
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Melampodium L.
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PlaceOfPublication
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Sp. P1. 921. 1753
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Note
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TYPE: M. americanum L.
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Description
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Annual herbs to perennial subshrubs; stems decumbent to erect, terete to finely striate, dichotomously branched. Leaves opposite, decussate, linear to ovate-rhombic, acu-minate to obtuse, the base attenuate to auriculate-connate, the upper surfaces glabrous to pilose, the lower surfaces glabrous to sericeous, the margin entire to toothed. Inflorescence of solitary heads arising from the middle and upper dichotomies; peduncles very short and stout to long and filiform. Heads radiate; involucre biseriate, the outer involucre spreading to cupulate, the bracts 2-5, subequal, the margins entire, separate to connate more than % their length., the adaxial surface glabrous, the inner involucral bracts each enclosing a single ray achene (each unit termed an "involucral fruit"), often extending upward into a hood or other apical appendage; receptacle paleaceous, convex, sometimes elevated on a short cylindrical stalk 2-3 mm above the base of the outer involucre; paleas scarious, conduplicate around disc corollas; ray florets fertile, 3-13, the ligules varying shades of yellow or cream-white, bi- or tri-dentate, the tube obsolete or very short, the style branches filiform, flattened, obtuse at the apex; disc florets perfect, sterile, 3-110, the corollas yellow-green to yellow-orange, regular, 5-lobed, the throat salverform-funnelform, the anthers brown, the style linear-capillaceous, unbranched, the ovary abortive, capped by a disc; pappus absent. Fruit an "involucral fruit" consisting of an achene enclosed by an adnate involucral bract, the achenes asymmetrically obovoid and laterally compressed; pappus absent. Chromosome numbers n = 9, 10, 11, 12, 18, 20, 23, 25+1, 27, 30, and 33.
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Habit
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Annual herbs to perennial subshrubs
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Note
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This is a genus of 37 species distributed primarily in Mexico and Central America. The most important morphological feature distinguishing Melampodium from other genera of the Heliantheae is the fusion of the ray achenes to the inner involucral bracts, which are often ribbed and/or sculptured variously, but never spiny (as in Acanthospermum).
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Reference
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Stuessy, T. F. 1972. Revision of the genus Melampodium (Compositae: Heliantheae). Rhodora 74: 1-70, 161-219.
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Key
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a. Outer involucral bracts 3 (rarely 4 or 5); peduncles stipitate-glandular (B. sect. Zarabellia) ...... 3. M. paniculatum aa. Outer involucral bracts 5; peduncles glabrous to lightly tomentose (A. sect. Serratura). b. Ligules 3.5-7 mm long ...... 2. M. divaricatum bb. Ligules less than 3 mm long ...... 1. M. costaricense
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