Centaurea solstitialis |
Centaurea macrocephala |
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St. Barnaby's thistle, yellow starthistle |
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Habit | Plants annual or biennial, 1–10 dm. | |
Stems | 1–many, branched from bases, tomentose. |
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Leaves | tomentose and scabrous to bristly, bases decurrent; basal and lower cauline blades often absent at maturity, 5–15 cm, pinnately dissected or lobed; petioles winged; upper cauline blades oblong to linear, 1–10 cm; margins entire or slightly dentate, sessile. |
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Inflorescences | cyme-like clusters or heads solitary. |
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Involucres | ovoid, 10–15 mm. |
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Florets | yellow, sterile florets ? fertile florets, fertile florets 13–20 mm. |
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Phyllaries | outer ovate; bodies green, palmately spiny; central spines stout, 10–25 mm; straw-colored; inner with smaller hyaline appendages. |
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Fruits | dimorphic; outer 2–3 mm, dark brown, glabrous; pappi 0; inner light brown or mottled, pappi of white bristles, 2–4 mm. |
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Heads | disciform, pedunculate. |
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2n | =16. |
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Centaurea solstitialis |
Centaurea macrocephala |
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Distribution | ||
Discussion | Disturbed areas, roadsides, woods, fields, pastures, streambanks. Flowering Jul–Oct. 0–2000 m. BR, BW, Col, CR, Est, Lava, Sisk, WV. CA, ID, NV, WA; throughout North America; Europe. Exotic. Centaurea solstitialis is an aggressive weed of pastures and rangeland in western North America, often forming dense stands. This species is cumulatively toxic to horses, potentially causing a disorder known as “chewing disease.” See also C. × gerstlaueri. |
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Source | Flora of Oregon, volume 2, page 215 Bridget Chipman |
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Sibling taxa | ||
Web links |
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