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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

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

1. Corolla yellow

2. Heads sessile or subsessile, subtended by leaf-like bracts ..... C. benedicta

2' Heads generally peduncled (if not, then subtending bracts reduced)

3. Corolla 25–30 mm ..... C. sulphurea

3' Corolla generally 10–20 mm

4. Central spine of main phyllaries 5–10 mm, ± purple ..... C. melitensis

4' Central spine of main phyllaries 10–25 mm, straw-colored ..... C. solstitialis

1' Corolla white to pink, blue, or purple

5. Main phyllaries ± spine-tipped

6. Main phyllary tip-spine 6–25 mm

7. Pappus 0 ..... C. calcitrapa

7' Pappus present, 0.3–2.5 mm

8. Involucre body 8–14 mm diam, widely ovoid ..... C. iberica

8' Involucre body 5–10 mm diam, narrowly ovoid ..... C. pouzinii

6' Main phyllary tip-spine 1–5 mm

9. Outer flower corollas expanded, ± ray-like, >> disk flower corollas, 25–35 mm, pink-purple ..... C. diluta (2)

9' Outer flower corollas not or barely expanded, = or slightly > disk flower corollas, 7–13 mm, white to pink or pale purple

10. Involucre 10–13 mm; disk flower corolla 12–13 mm ..... C. diffusa

10' Involucre 7–8 mm; disk flower corolla 7–9 mm ..... C. virgata subsp. squarrosa

5' Main phyllaries not spine-tipped

11. Annual

12. Herbage ± tomentose; disk flower corolla 10–15 mm ..... C. cyanus

12' Herbage puberulent or ± glabrous, sometimes thinly cobwebby; disk flower corolla ± 20 mm ..... C. diluta (2)

11' Biennial or perennial herb

13. Outer and inner flowers bisexual; corollas all ± equal ..... C. jacea subsp. nigra

13' Outer flowers sterile, inner flowers bisexual; sterile flower corollas > bisexual flower corollas

14. Herbage densely gray-tomentose ..... C. cineraria

14' Herbage ± green, sometimes thinly cobwebby

15. Involucre 10–13 mm ..... C. stoebe subsp. micranthos

15' Involucre 15–18 mm

16. Phyllary appendages scarious, light brown, concave, entire to coarsely dentate ..... C. jacea subsp. jacea

16' Phyllary appendages light to dark brown, flat to ± concave, coarsely dentate to dissected into fine, wire-like lobes ..... C. jacea nothosubsp. pratensis

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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