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ASTERACEAE (Compositae) SUNFLOWER FAMILY

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 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

CENTAUREA KNAPWEED, STAR-THISTLE
Annual to perennial herb. Stem: prostrate to erect, generally ± branched, generally ribbed, occasionally winged. Leaf: basal and cauline, alternate; proximal generally 1–2-pinnately lobed; distal generally ± reduced. Inflorescence: heads disciform or radiant (discoid); involucre cylindric to hemispheric; phyllaries graduated in 6–many series, generally ± ovate, scarious-margined, tip appendages fringed to spiny; receptacle flat, epaleate, long-bristly. Flower: corolla white to pink, purple, or yellow, tube long, distally bent; outer flowers generally sterile, corolla 3–10-lobed, ± bilateral, reduced, inconspicuous or expanded and spreading, ± ray-like; inner flowers bisexual, corolla ± radial; anther base tailed, tip oblong; style tip cylindric, minutely hairy distal to hairy ring, branches very short. Fruit: ± barrel-shaped, ± compressed, attached ± at side; pappus 0 or generally of stiff, unequal bristles or narrow scales.
± 500 species: especially Eurasia, northern Africa; some cultivated. (Greek: plant name associated with Chiron, a centaur) [Keil & Ochsmann 2006 FNANM 19:181–194] Many noxious or invasive weeds. Centaurea nigrescens Willd. not naturalized.

Key to Centaurea

C. jacea nothosubsp. pratensis (W.D.J. Koch) Celak.
NATURALIZED
Inflorescence: heads radiant (discoid); peduncle swollen below head or not; phyllary tip appendages ± scarious, light to dark brown, flat to ± concave, coarsely dentate to dissected into fine, wire-like lobes. Flower: disk flower corolla 15–22 mm. Fruit: pappus scales <= 1 mm, white or tan.
2n=22, 44. Grassland, disturbed places, montane forest; 150–1100 m. Outer North Coast Ranges, Cascade Range; to southern Canada, eastern United States; native to Europe or locally derived from hybridization of parental taxa native to Europe. [Centaurea ×moncktonii C.E. Britton; Centaurea ×pratensis Thuill., illeg.] Variable, outcrossing derivative of fertile hybrid (Centaurea jacea subsp. jacea × Centaurea jacea subsp. nigra). Populations show much plant-to-plant variation, often with some individuals approaching one or the other parental subsp. Aug–Oct {Noxious weed} [Online Interchange]

Previous taxon: Centaurea jacea subsp. nigra
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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Aug 30 2014
Citation for this treatment: [Author of taxon treatment] 2013. Centaurea, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=93858, accessed on Aug 30 2014

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Geographic subdivisions indicated for the distribution of Centaurea jacea subsp. pratensis 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.
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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.