Appearance''Centaurea solstitialis'' is an annual herb from the Asteraceae family. During the vegetative stage if forms a rosette of non-spiny leaves . As the summer approaches, it produces a flowering stem which will produce numerous spinous capitula containing numerous yellow flowers. Flowers within capitula are pollinated by insects and each capitula will produce a mix of pappus and non-pappus seeds. It is an annual semelparous species, and will die after reproduction is completed, normally by the end of the summer.
Naming''Centaurea solstitialis'' grows as a balanced part of the ecosystems in Eurasia, where it is kept in check by an assortment of natural herbivore enemies and other plants that have co-evolved with it in its native habitat. However, it has been introduced in several parts of the world, including Australia, Argentina, Chile, and the USA. In many of these non-native regions, where the particular array of natural biological controls found in the native regions do not exist, it has become an invasive species and noxious weed.The introduction of ''Centaurea solstitialis'' in North America probably occurred in California sometime after the start of the California Gold Rush, as a fodder seed contaminant in imported Chilean-harvested alfalfa seed, also known as Chilean clover . Introduction in other parts of the world is poorly known.
In California, Yellow star-thistle was dispersed into agricultural fields, and immediately took hold in the state's Mediterranean-type climate areas. Human factors, such as mowing, land grading for development and roads, domestic animal grazing, and disturbance of the soil surface for agricultural tillage and wildland firebreaks have and continue to contribute to the successful thriving and spread of this plant. Yellow starthistle is now a very common sight in vacant lots and fields, along roadsides and trails,in pastures and ranch lands, and in parks, open-space preserves and natural areas.Species similar to ''Centaurea solstitialis'' are purple star-thistle , sulphur star-thistle , Maltese star-thistle , and rough star-thistle .
Habitat''Centaurea solstitialis'' is a weed also on its native European range , 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 , 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. This makes this species a candidate case for incipient ecological speciation.
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