Yellow Starthistle Information
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Taxonomy & id
Reproduction
-Flower pollination
-Flower & seed dev
-Seed dispersal
Germination
& dormancy
-Seed prod & types
-Seed development
-Germination
-Stress & germ
-Seasonal germ
-Seed longevity
Growth & establishment
-Seedling establish
-Roots
--growth
& dev
--water use
---competition
-Shoots
--growth &
dev
--light
--temperature
--allelopathy
Biology and Ecology
Yellow starthistle is a winter annual widely distributed in the Central Valley and adjacent foothills of California and also common in many other western states. It is currently spreading in mountainous regions of California below 7,000 ft and in the Coast Ranges, but is less commonly encountered in the desert, high mountains and moist coastal sites. Yellow starthistle is typically found in full sunlight and deep, well-drained soils, where annual rainfall is between 10-60 inches.
Taxonomy and identification
Of the 12 species of Centaurea in California, all are non-native and 9 have purple to white flowers. The three yellow flowered species include Centaurea solstitialis (yellow starthistle), Centaurea melitensis (tocalote, Napa or Malta starthistle), and Centaurea sulphurea (Sicilian starthistle). In addition to having yellow flowers, these three species also have long sharp spines associated with their flowerheads. The Jepson Manual (1993) to the California flora separates the three species by the following key.
Corolla generally >25 mm
………………….......… Centaurea sulphurea
Corolla generally 10-20 mm
Central spines of main phyllaries 5-10 mm
.... Centaurea melitensis
Central spines of main phyllaries 10-25 mm
.... Centaurea solstitialis
For a more detailed description of the identification and distribution of these three species read the yellow-flowered Centaurea fact sheet. Photos of seedlings, bolting plants, flowering plants, flowerheads, and seeds (achenes) can also be viewed. In other western states, Centaurea macrocephala (bighead knapweed) also has yellow flowers but does not have long sharp spines on the flowerheads (Roché 1991c). Roché and Roché (1991a, 1993) have published other excellent keys to the western species of Centaurea.
Researchers have studied a variety of yellow starthistle populations to determine is there if genetic diversity or biotype differences throughout its range. Sheley et al. (1983a, b, c) found numerous significant differences in morphological characteristics among 16 populations of yellow starthistle collected from Oregon, Washington, Idaho and California, but these differences were not correlated with location or precipitation zones. They suggested that populations of starthistle might be composed of significantly different genetic makeup. After analyzing protein bands in 13 genotypically differing populations of yellow starthistle collected in Washington, Idaho, and California, no significant differences were found (Schumacher et al. 1982).
Using allozyme electrophoretic surveys, Sun (1997) conducted a more detailed analysis of the genetic structure of 22 yellow starthistle populations from California, Washington and Idaho, including the southern and northern extremes of its distribution. Interestingly, high levels of allozyme variation occurred within populations. The level of genetic diversity was similarly high in all populations tested, with little interpopulation divergence. The author suggested that yellow starthistle was probably colonized by many genotypes in the Pacific States and that high levels of gene flow have occurred among local populations.
