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Maltese starthistle, tocalote

St. Barnaby's thistle, yellow starthistle

Habit Plants annual, 1–10 dm. Plants annual or biennial, 1–10 dm.
Stems

branched above, sparsely tomentose;

gland-dotted.

1–many, branched from bases, tomentose.

Leaves

villous, thinly to densely tomentose;

gland-dotted;

basal and lower cauline blades oblong to oblanceolate, 2–15 cm;

margins dentate, pinnately lobed or entire, petiolate to tapering at base; upper cauline blades linear to oblong, 1–5 cm, bases decurrent;

margins dentate to entire.

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.

Inflorescences

1–few in corymb-like arrays or heads solitary.

cyme-like clusters or heads solitary.

Involucres

ovoid, 8–15 mm.

ovoid, 10–15 mm.

Florets

yellow, sterile florets ? fertile florets, fertile florets 10–14 mm.

yellow, sterile florets ? fertile florets, fertile florets 13–20 mm.

Phyllaries

outer ovate, bases spiny-fringed;

surfaces tomentose to glabrate;

central spines slender, 5–10 mm, often purple; inner entire; acute or spine-tipped.

outer ovate;

bodies green, palmately spiny;

central spines stout, 10–25 mm; straw-colored; inner with smaller hyaline appendages.

Fruits

2.5–3 mm, white or light brown, finely hairy, pappi of unequal, white bristles, 1.5–3 mm.

dimorphic; outer 2–3 mm, dark brown, glabrous;

pappi 0; inner light brown or mottled, pappi of white bristles, 2–4 mm.

Heads

disciform.

disciform, pedunculate.

2n

=24.

=16.

Centaurea melitensis

Centaurea solstitialis

Distribution
[WildflowerSearch map]
[BONAP county map]
[WildflowerSearch map]
[BONAP county map]
Discussion

Disturbed areas, roadsides, open woods, fields, pastures. Flowering May–Jul. 0–700 m. CR, ECas, Est, Sisk, WV. CA, ID, NV, WA; scattered in North America; Africa, Asia, Europe. Exotic.

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.

Source Flora of Oregon, volume 2, page 214
Bridget Chipman
Flora of Oregon, volume 2, page 215
Bridget Chipman
Sibling taxa
C. benedicta, C. calcitrapa, C. cyanus, C. diffusa, C. iberica, C. jacea, C. jacea x Centaurea nigra, C. montana, C. nigra, C. nigrescens, C. solstitialis, C. stoebe, C. virgata
C. benedicta, C. calcitrapa, C. cyanus, C. diffusa, C. iberica, C. jacea, C. jacea x Centaurea nigra, C. melitensis, C. montana, C. nigra, C. nigrescens, C. stoebe, C. virgata
Web links