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(Last Modified On 6/20/2013)
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(Last Modified On 6/20/2013)
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Genus
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Senecio L.
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PlaceOfPublication
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Sp. P1. 866. 1753
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Note
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TYPE: S. vulgaris L
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Description
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Herbs, shrubs, small trees or lianas. Leaves alternate, simple, pinnately veined, or in 1 species, palmately veined. Inflorescence a few-many-headed corymbiform cyme arising terminally or in the axils of the upper leaves, or occasionally heads solitary. Heads radiate or discoid, rarely disciform, red to orange-red or yellow, sometimes ochroleucous; principal involucral bracts of equal length in a single series or obscurely divisible into an inner and outer series, usually subtended by a calyculus of 10 or fewer irregular bractlets; receptacle flat to gently convex, naked, sometimes obscurely alveolate or with minute hairlike paleas irregularly disposed among the achenes, conspicuous paleas lacking; ray florets fertile, in a single series, the ligule usually well developed but sometimes reduced and inconspicuous, ray florets sometimes absent; disc florets fertile, bisexual, the style branches variously tipped with a penicilliate tuft of hairs to a distinct, triangular appendage. Achene terete or ribbed, glabrous or variously pubescent; pappus of a single series of white, capillary bristles.
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Habit
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Herbs, shrubs, small trees or lianas
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Distribution
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A huge complex of more than 1500 species in both the Old and New Worlds
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Note
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Senecio is readily divisible into semidistinct groups. Some contemporary botanists advocate the recognition of several segregate genera, but the broad traditional concept of Senecio has been maintained in this treatment.
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Reference
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Beaman, J. H., D. C. D. Dejong & W. P. Stoutamire. 1962. Chromosome studies in the alpine and subalpine floras of Mexico and Guatemala. Amer. Jour. Bot. 49: 41-50. Cabrera, A. L. 1950. Notes on the Brazilian Senecioneae. Brittonia 7: 53-74. Cuatrecasas, J. 1955. A new genus and other novelties in Compositae. Brittonia 8: 151-153. Greenman, J. M. 1901. Monographie der nord-und centralamerikanischen Arten der Gattung Senecio. 1 Teil. Leipzig. 37 pp. [Reprinted in Bot. Jahrb. Syst. 32: 1-33. 1902.] Robinson, H. & R. D. Brettell. 1973. Studies in the Senecioneae (Asteraceae) V. The genera Psacaliopsis, Barkleyanthus, Telanthophora and Roldana. Phytologia 27: 402-439. Williams, L. 0. 1975. Tropical American plants, XVIII. Phytologia 31: 435-447.
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Key
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a. Erect herbs, shrubs or small trees, not scrambling lianas. b. Cauline leaves palmately veined ...... 6. S. heterogamus bb. Cauline leaves pinnately veined. c. Leaves densely white lanate-tomentose throughout, at most glabrate on the upper leaf-surfaces ...... 8. S. oerstedianus cc. Leaves variously pubescent to glabrous but not densely white-lanate-tomentose. d. Leaves large, blades 15-35 cm long, deeply sinuate with 3-6 conspicuous sinuses on each side of the leaf ...... 2. S. arborescens dd. Leaves normally smaller, dentate to entire but not both large and deeply sinuate. e. Involucral bracts 13-17(-18), the calyculate (basal) bracts 6 or more, conspicuous, often more than 5 mm long, the involucre often purplish ...... 3 . S . b o q u e te n sis ee. Involucral bracts ca. 8, the calyculate (basal) bracts 4 or fewer, rarely more than 4 mm long. f. Heads narrowly cylindrical; involucral bracts linear-oblong, more than 8 mm long; ligules ca. 10 mm long in dried specimens ...... 5. S. cooperi ff. Heads broader upwards, at least at maturity; involucral bracts lanceolate-spatulate, 6-7 mm long; ligules 5-8 mm long ...... 7. S. megaphyllus aa. Lianas. g. Heads large, campanulate; principal involucral bracts 30-40'; ray florets 18-24, the style branches surmounted by distinctly expanded, papillose, triangular tips ...... 4. S. confusus gg. Heads smaller; principal involucral bracts 10 or fewer; style branches surmounted by penicilliate hairs. h. Heads radiate, -the ligules long and narrow, ca. 10-15 mm long, less than 1 mm wide; leaves, especially the lower surfaces, with stipitate-stellate hairs ...... 1. S. angustiradiatus hh. Heads disciform or with ligules less than 1 mm long; leaves glabrescent, sometimes with scattered simple hairs ...... 9. S. parasiticus
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