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Concept
Centaurea solstitialis
Summary
Centaurea solstitialis, the yellow star-thistle, is a species of thorny plant in the genus Centaurea, which is part of the family Asteraceae. A winter annual, it is native to the Mediterranean Basin region and invasive in many other places. It is also known as golden starthistle, yellow cockspur and St. Barnaby's thistle (or Barnaby thistle).
Centaurea solstitialis is an annual herb from the family Asteraceae. During the vegetative stage it forms a rosette of non-spiny leaves, between in diameter. As the summer approaches, it produces a flowering stem up to in height. The leaves at the base are lobed and range between in length, while the ones on the stem are unlobed and smaller. Between May and October, the stem produces numerous spinous flower heads (capitula) about across, containing between 10–50 yellow flowers, with spines between . Flowers within capitula are pollinated by insects and each capitula produces 10–50 seeds, some with and some without a pappus. It is an annual semelparous species, and will die after reproduction is completed, normally by the end of the summer.
Similar species include purple star-thistle (Centaurea calcitrapa), sulphur star-thistle (C. sulphurea), Maltese star-thistle (C. melitensis), and rough star-thistle (C. aspera). Bachelor's button (C. cyaneus) is a relative.
Centaurea solstitialis is a weed also on its native European range (e.g., Turkey, Greece, Italy, France, Spain), consequently, it inhabits highly disturbed ruderal habitats, being typically found on roadsides and cereal crop margins. After introduction in several parts of the world as an exotic species (e.g., Australia, Argentina, Chile, the United States), it has developed local adaptations to the different habitats colonized, and an incipient level of reproductive isolation between native and non-native ranges has been detected—a case of ecological speciation.
Star-thistle is a valuable source of pollen, thus nectar for pollinators. Yellow star-thistle, a noted pest plant, is a major nectar source for many central valleys and foothill butterflies.
Official source
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