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David J. Keil, except as noted

Annual to tree. Leaf: basal and/or cauline, alternate, opposite, rarely whorled, simple to 2+ × compound. Inflorescence: 1° inflorescence a head, resembling a flower, of several types (see below), 1–many in generally ± cyme-like cluster; each head generally with ± calyx-like involucre of 1–many series of phyllaries (involucral bracts); receptacle of head flat to conic or columnar, paleate (bearing paleae = receptacle bracts) or epaleate; flowers 1–many per head. Flower: bisexual, unisexual, or sterile, ± small, of several types (see below); calyx 0 or modified into ± persistent pappus of bristles, scales, and/or awns; corolla radial or bilateral (0), lobes generally (0)3–5; stamens 4–5, filaments generally free, generally fused to corolla at tube/throat junction, anthers generally fused into cylinder around style, anther base generally rounded or cordate (deeply sagittate or with tail-like appendages), tip (= flattened appendage) generally projecting beyond pollen sac; pistil 1, 2-carpeled, ovary inferior, 1-chambered, 1-seeded, placenta basal, style 1, tip generally ± 2-branched (except in some staminate disk flowers), branch tips truncate or generally bearing ± brush-like appendages; stigmas 2, generally on adaxial faces of style branches. Fruit: achene (also called a cypsela) (drupe in Chrysanthemoides), cylindric to ovoid, sometimes compressed, generally deciduous with pappus attached.
± 1500 genera, 23000 species: worldwide, many habitats. Flower and head types differ in form and sexual condition. A disk flower has a generally radial corolla, with a cylindric tube, expanded throat, and generally 5 lobes. Disk flowers are generally bisexual and fertile but occasionally staminate with reduced ovaries. Discoid heads comprise only disk flowers. A radiant head is a variant of a discoid head, with peripheral disk flower corollas expanded, often bilateral. A ray flower corolla is bilateral, generally with a slender tube and flattened petal-like ray (single lip composed of generally 3 lobes). Ray flowers are generally pistillate or sterile (occasionally lacking styles). Radiate heads have peripheral ray flowers and central disk flowers. Disciform heads superficially resemble discoid heads, with pistillate or sterile flowers that lack rays, together with or separate from disk flowers. A ligulate flower is bisexual, with a bilateral, generally ephemeral corolla and 5-lobed ligule. Liguliflorous heads comprise only ligulate flowers. See glossary p. 31 for illustrations of family characteristics. Echinops sphaerocephalus L., Gaillardia aristata Pursh, Gaillardia pulchella Foug., Hymenothrix loomisii S.F. Blake, Tagetes erecta L., Thelesperma megapotamicum (Spreng.) Kuntze are waifs. Melampodium perfoliatum Kunth, historic urban waif. Ageratum conyzoides L., Guizotia abyssinica (L. f.) Cass., Santolina chamaecyparisus L., orth. var. are rare or uncommon escapes from cultivation. Dyssodia papposa, Ismelia carinata (Schousb.) Sch. Bip. [Chrysanthemum carinatum Schousb.], Mantisalca salmantica (L.) Briq. & Cavill. are historical or extirpated waifs in California. Inula helenium L. not documented in California. Taxa of Aster in TJM (1993) treated here in Almutaster, Eucephalus, Eurybia, Ionactis, Oreostemma, Sericocarpus, Symphyotrichum; Chamomilla in Matricaria; Cnicus in Centaurea; Conyza in Erigeron and Laennecia; Dugaldia in Hymenoxys; Erechtites in Senecio; Hymenoclea in Ambrosia; Lembertia in Monolopia; Osteospermum ecklonis in Dimorphotheca; Picris echioides in Helminthotheca; Prionopsis in Grindelia; Raillardiopsis in Anisocarpus and Carlquistia; Schkuhria multiflora in Bahia; Trimorpha in Erigeron; Venidium in Arctotis; Whitneya in Arnica. Taxa of Arida in TJM2 (2012) treated here in Leucosyris. —Scientific Editors: David J. Keil, Bruce G. Baldwin.
Unabridged note: Largest family of vascular plants in California and of eudicots globally.

Key to Asteraceae

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.
± 200 species: North America, Eurasia. (Greek: thistle) [Keil 2006 FNANM 19:95–164] Taxa difficult, variable, incompletely differentiated, hybridize. Exceptional white-flowered plants occur in most taxa with pigmented corollas; these generally not treated in key.
Unabridged references: [Kelch & Baldwin 2003 Molec Ecol 12:141–151]
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.

Key to Cirsium

C. scariosum Nutt. MEADOW THISTLE
Biennial or short-lived perennial herb, 0.5–10+ dm. Stem: often 0 or short, occasionally erect or bushy-branched, often ± fleshy, glabrous to loosely tomentose, occasionally coarse-hairy. Leaf: glabrous to loosely tomentose adaxially, glabrous to densely tomentose abaxially; often all basal, ± petioled, cauline 0 or well distributed, proximal 1–4 dm, tapered or spiny-petioled, oblong to oblanceolate, unlobed to deeply lobed, occasionally with 2° lobes or teeth, main spines 2–10+ mm. Inflorescence: heads generally crowded, ± sessile, closely subtended by basal rosette or in ± tight, generally leafy clusters at stem tips; involucre 2–4.5 cm, 2–5 cm diam, ovoid to bell-shaped, glabrous; outer phyllaries lance-linear to ovate, ± entire, tip-spine 1–12 mm, ascending, inner tips narrow and entire or expanded and irregularly toothed or cut, flat or crinkled. Flower: corolla 20–40 mm, ± white to purple, tube 7–24 mm, throat 4–12 mm, lobes 4–10 mm; style tip 3.5–8 mm. Fruit: 3–6.5 mm; pappus 15–35 mm. Variable complex of intergrading races. Extreme forms very different. Stemmed or stemless forms may occur in same population or not. Some plants not readily assignable to variety. Needs study. [Online Interchange]
Unabridged note: Past taxonomic treatments have variably recognized members of this complex as multiple species, some as subspecies and/or varieties or have merged all or most variants into a single polymorphic sp. with extraordinary variability. See Keil 2006 for discussion. Hybrids are known or suspected in many cases where forms of Cirsium scariosum meet other native thistle species. Unusual variants in herbaria may represent unrecognized hybrids or their descendants.

C. scariosum var. americanum (A. Gray) D.J. Keil DINNERPLATE THISTLE
Stem: generally 0. Leaf: adaxially glabrous or jointed-hairy, abaxially gray-tomentose, hairs jointed or not; main spines generally 2–7 mm. Inflorescence: heads 1–many, sessile or subsessile, closely subtended by basal rosette (occasionally stemmed plants in same population); involucre 1.5–3 cm; outer phyllary tip-spine 1–12 mm, inner tips entire or abruptly expanded to scarious, irregularly toothed appendage. Flower: corolla white or pink-tinged.
2n=34. Wet to dry meadows, grassy forest openings, open sites; 1600–3500 m. High Cascade Range, High Sierra Nevada, Warner Mountains; to Oregon, Idaho, Wyoming, Colorado, northern Baja California. Jun–Aug [Online Interchange]

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora,, accessed on Mar 27 2015
Citation for this treatment: [Author of taxon treatment] 2013. Cirsium, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on Mar 27 2015

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Geographic subdivisions indicated for the distribution of Cirsium scariosum var. americanum Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).

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Data provided by the participants of the Consortium of California Herbaria.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.