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Barnaby's Thistle

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).[1]

barnaby's thistle

Similar species include purple star-thistle (Centaurea calcitrapa), sulphur star-thistle (C. sulphurea), Maltese star-thistle (C. melitensis), and rough star-thistle (C. aspera).[3] Bachelor's button (C. cyaneus) is a relative.[2]

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.[8] Star-thistle populates ground that has been abused: dry, compacted, or scraped clean. A plant with a taproot system, it has a crucial role in restoring the soil by bringing up vital micronutrients. Similar to many plants classified as 'weeds', they (in the words of Mark Schonbeck) "quickly establish in, protect, and restore soil that has been left exposed by natural and human-caused disturbances".[9]

The yellow star-thistle plant has the ability to create monotypic stands and habitats in the cultivated soil of fields, graded dirt sites, and disturbed natural ecosystem lands. Its colonization eliminates and prevents other plant species from growing, terminating the habitat's biodiversity. Extensive spreading monotypic fields of yellow star-thistle are not uncommon. Its growth plasticity, competitiveness, preference for the Mediterranean climate, and a lack of natural herbivore enemies and co-evolved species, make it a very successful invader. The plant is an invasive pest in field crops, degrades native plant habitats and natural ecosystems, prevents the grazing of domestic animals in rangelands, and is a physical barrier to indigenous animal movement in wildlands.[10]

The introduction of C. 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 (Trifolium macraei).[11] Star-thistle has been introduced throughout North and South America, Africa, and Europe.[12]

In California, yellow star-thistle was dispersed into agricultural fields and immediately took hold in the state's areas with a Mediterranean climate. 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 star-thistle 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.

By 1970,[14] yellow star-thistle had reached 23 U.S. states.[11] According to the U.S. Forest Service, as of 2006 the plant has been reported present in 41 of the 48 contiguous U.S. states, with the only exceptions being Maine, Vermont, and five of the Deep South states (Arkansas, Louisiana, Mississippi, Alabama, and Georgia).[15] The plant is considered an invasive species in six of the 41 states: California, Oregon, Washington, Idaho, Utah, and New Jersey.

Most herbicides used for controlling yellow star-thistle are registered for range lands, right-of-way, and other non-crop areas. Many auxin-like or growth-regulator herbicides are used for post-emergence control, including 2,4-D, aminopyralid, clopyralid, dicamba, picloram and triclopyr. Alternatively, glyphosate may be used. Pre-emergence herbicides used for yellow star-thistle control include chlorsulfuron and sulfometuron. Pre-emergence and post-emergence herbicides may be used effectively together to kill growing plants as well as any new seedlings that may emerge from the copious soil seed bank often produced by yellow star-thistle. Controlled burning may also be used in conjunction with clopyralid application as an effective integrated approach to yellow star-thistle management.[16]

A yellow star-thistle biotype resistant to picloram was discovered in a pasture near Dayton, Ohio, in 1988. This biotype was determined to have cross resistance to other auxin-like herbicides, especially clopyralid.[18] Resistance was discovered to be conveyed by a single nuclear recessive gene.[19]

Yellow star-thistle is sometimes resistant to removal methods such as mowing and burning, because of its long root system and the seeds' ability to withstand fire. The plant has been the target of biological pest control programs with positive results. Seven types of seed-feeding insects have been released (one accidentally) to control the plant.[21][22]

A variety of the rust fungus Puccinia jaceae var. solstitialis, first released in July 2003 on a ranch in the Napa Valley, has shown promise as an agent against yellow star-thistle,[32][33] dramatically damaging leaves and hampering growth.[33] The rust causes widespread pathology in the leaves of the plant and slows its dispersal. The fungus Synchytrium solstitiale (Synchytrium of phylum Chytridiomycota) is also being considered as an agent of biological control.[34]

Grazing by goats, cattle, or sheep can be effective in controlling yellow star-thistle.[35] Goats will eat star-thistle even in its spiny stage.[36] Because yellow star-thistle growth is particularly difficult to inhibit in canyon rangelands since its remoteness limits control options, goats and other herbivores have become an excellent option to curb the plant's spread. According to one study, grazing has decreased yellow star-thistle presence by 58% when compared to the study's controls. Subplots also showed a 94% decrease in seed heads after only three years of experimentation.[37]

California researchers (Thomsen et al., 1996) tested mowing, controlled sheep grazing and subterranean clover plantings to control star-thistle growth. According to the researchers, subclover would help fill the void left by star-thistle populations.[38]

Yellow star thistle is a winter annual in the Asteraceae (daisy) family native to southern Europe and North Africa. It grows on rangelands, pastures, agricultural areas, along highways or roads, railroad tracks, and other transportation or communication lines. It is dependent on seed production for growth and spread. A distinguishing characteristic is the bracts of the yellow flower heads contain stout, needle-like, straw-colored spines one to two inches long that radiate from the flower head in the shape of a star. The bracts are light green, variably covered in cobwebby hairs and may become smooth.

Yellow star thistle has a stout taproot and/or pubescent stems. Root growth during the winter and early spring is rapid and can extend well beyond 3 feet in depth. The stem is erect, slender, hairy and branching, and can grow up to three feet tall.

Genus name Centaurea came from the popular name of various plants in the late 14th century, from Medieval Latin centaurea, from Latin centaureum, from Greek kentaureion, meaning "centaur", so called because the plant's medicinal properties were discovered by Chiron the centaur. Specific epithet solstitialis pertains to the longest day of the year. This is in reference to the ability of yellow star thistle to flower very late into the summer.

Habitat: disturbed Communities: weed, characteristic of disturbed placesName Status:Accepted by JEF + PLANTSAlternate Names: PLANTSLeucantha solstitialisInformation about Centaurea solstitialis from other sourcesJepson eFloraUSDA PLANTS Profile(CESO3)Photos on CalfloraPhotos on CalPhotosGoogle ImagesPhotos on iNaturalistITIS Original Publication citationInternational Plants Names IndexSearch (Flora of North America)BONAP Distribution MapCal-IPC Profile rating: highConsortium of California Herbaria 2Add an ObservationLocation SuitabilityDistribution by County FEIS: DISTRIBUTION AND OCCURRENCE: "It is likely that there were multiple introductions of yellow starthistle to the United States ... and that contaminated alfalfa seed (Medicago sativa) was the primary vehicle for these introductions ... . Yellow starthistle seeds were found in adobe bricks from the period between 1824 and 1848 in California (Hendry 1931, ...). The plant was first collected in Oakland, California in 1869 and was most likely introduced from Chile, while introductions from 1899 to 1927 appear to be from Turkestan, Argentina, Italy, France and Spain "

Star thistles, including knapweeds and cornflowers, belong to the Centaurea genus. These in turn are allied with thistles belonging to the Asteracea family of plants. Centaurea is probably one of the largest sources of all thistle honeys. Being good producers of nectar, along with their tendency to grow together (often as an invasive weed), may make them the primary source of nectar at that time of the year. The result is varietal honeys from many different species of Centaurea.

Centaurea species are moderate nectar producers and as such are sought after by many insects besides honey bees including some endangered butterflies. Unfortunately there is a general prejudice against Centaurea, especially in North America where Diffuse Knapweed (C. diffusa), Spotted Knapweed (C. maculosa) and Yellow Starthistle (C. solstitialis) are invasive, robust weeds taking over and pushing out native species. But on a per species basis they are inoffensive and beautiful, colorful plants, often endemic to a particular place and supporting insect life of that area. In these cases, they can be an aid to agriculture by attracting harmful beetles and insects away from crops. The beautifully blue Cornflower has seen use throughout history for infections and decoration, and the Basketflower too, is cultivated for its beautiful bloom. 041b061a72

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