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Index to accepted names and synonyms:
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|Family: Asteraceae (Compositae)||View Description||Dichotomous Key|
|Genus:||View Description||Dichotomous Key|
|Species:||View Description||Dichotomous Key|
Habit: Taprooted annual, biennial, or short-lived perennial herb that flowers once, or multi-flower perennial herb with taprooted rosettes arising from runner roots or from simple to branched caudex; glabrous to cobwebby or +- densely tomentose with long, fine, slender hairs, sometimes with thicker multicellular, jointed hairs that often appear crinkled, shining, iridescent when dry. Stem: generally erect. Leaf: basal and proximal cauline generally tapered or +- wing-petioled, generally wavy-margined, dentate to generally pinnately lobed and +- dentate, lobes and teeth spine-tipped, generally spiny-ciliate, faces glabrous to tomentose, especially abaxially; distal generally sessile, +- reduced. Inflorescence: heads discoid, 1--many, center head of cluster generally larger, generally erect; involucre +- cylindric to ovoid, spheric, or bell-shaped, persistent when dry; phyllaries many, graduated in 5--20 series, generally entire (spiny-ciliate or with irregularly toothed or cut scarious margin or distal appendage), outer and middle generally spine-tipped, in some species midrib with sticky-resinous ridge (milky when fresh, dark when dry, occasionally very narrow); inner phyllaries generally narrow, flat, tips straight or twisted; receptacle flat, long-bristly, epaleate. Flower: +- many, generally bisexual (unisexual in Cirsium arvense); corolla +- radial, white to red or purple, tube long, narrowly cylindric, throat cylindric, lobes linear; anther tube colored same as corolla or not, anther base sharply sagittate, tip linear or oblong; style generally exserted, tip cylindric, branches very short. Fruit: ovoid, thick or +- compressed, straw-colored or tan to dark brown, glabrous; attachment scar slightly angled; pappus bristles many, +- flattened proximally, plumose, weakly fused at base, often deciduous in ring, white to brown.
Species In Genus: +- 200 species: North America, Eurasia. Etymology: (Greek: thistle) Note: Taxa difficult, variable, incompletely differentiated, hybridize. Exceptional white-flowered plants occur in most taxa with pigmented corollas; these generally not treated in key.
Unabridged Note: Native thistles are part of an apparently actively evolving group of species with many geog and ecological races and growth forms. Morphologically divergent species often are able to hybridize; unrecognized hybridization or intergradation often complicates identification. Stature, growth form, and proportions are subject to environmental influence.
eFlora Treatment Author: David J. Keil
Jepson Online Interchange
Key to CirsiumPrevious taxon: Cichorium intybus
Next taxon: Cirsium andersonii
Citation for this treatment: David J. Keil 2017. Cirsium, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=384, accessed on April 26, 2017.
Citation for the whole project: Jepson Flora Project (eds.) 2017. Jepson eFlora, http://ucjeps.berkeley.edu/eflora/, accessed on April 26, 2017.