Kingdom:
Plantae
Division:
Magnoliophyta
Class:
Magnoliopsida
Order:
Asterales
Family:
Asteraceae
Genus:
Centaurea
Species:
Centaurea
solstitialis
(ITIS 2003)
(Photo by CDFA © 2001)
In progress
12/11/2003
The Biogeography of the Yellow Starthistle (Centaurea
solstitialis).
by Jeffery J. Skahill, student in Geography 316 Fall 2003
Thank you for visiting our site. This web pages was written by a student in
Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.
All photos and maps are posted with specific copyright permission for the express use of education
on these web pages. The students have tried to be as accurate as possible with
the information provided and sources and references are cited at the end of each page.
Species Name:
Yellow Starthistle
| Taxonomic
Hierarchy
Kingdom:
Plantae (ITIS 2003) |
(Photo by CDFA © 2001) |
Description of Species and Natural History:
| Yellow starthistle is a winter annual that occasionally exhibits biennial habits by flowering only in its second year (Maddox 1985). It germinates in the fall after forming a rosette in the late winter or early spring. The appearance of the rosette makes it difficult to distinguish from any number of other weeds. When the plant bolts, it produces a dozen or more branches with wide, flat, green leaves and varies in height from six inches to greater than three feet. In a Mediterranean climate, it bolts in the early summer, flowers in late May through September, and finally disseminates mature seeds in early July through |
 (Photo by George W. Hartwell © 2003) |
| October (Maddox 1985). The flower looks like bright yellow dandelions reaching upwards with sharp spines extending horizontally underneath the flower. It has dimorphic achenes, or seeds, producing both pappus-bearing and non-pappus bearing seeds. A pappus is a seed with featherlike hairs common in the Asteraceae family, but rarely encountered in the genus Centaurea. The versatility of the seeds allow the species to colonize a greater variety of habitats. The pappus-bearing seeds use wind and mechanical agitation to disperse, while the non-pappus-bearing seeds remain on the head until late November or December when the involucral bracts, or subtending flower structure, rot causing the seeds to fall to the ground (Maddox 1985). |
 (Photo by CDFA © 2001) |
An individual plant can produce between 1000 and 10,000 seeds. Mature fields of yellow starthistle have been estimated to contain up to 5-7 million plants per hectare (Callihan 1993). A pappus-bearing achene is generally light to dark brown with tanstriations. It grows in a series of rings at the center of the seed head (Benefield 2001). Alternatively, the non-pappus-bearing achenes are dark brown or even black without striations. They grow in a single ring around the edge of the seed head. |
Distribution:
| Centaurea solstitialis originates from southern and central Europe, and is widely believed to have been introduced to California via alfalfa seed in the early 1800’s. Studies have found the weed present in bricks made by Mexicans after 1824. The earliest known herbarium collection of the weed in California was from a 1869 sample in Oakland (Maddox 1985). It is generally believed that multiple introductions of yellow starthistle have occurred since the early 1800’s through contaminated crop seeds (Gerlach 1997). It lives at elevations between sea level to 2500 meters (Maddox 1985). It can survive in a variety of soils, from deep well drained soils to shallow rocky soils. It has beenfound in regions receiving between 25 to 100 cm of rain annually. Almost every semiarid to semi-humid rangeland in the western portion of the United States is vulnerable to infestation by the weed. Most achenes fall within 1.2 meters of the parent plant so their natural movement into new regions is slow, but "since the 1960's three factors greatly contributed to its |
| further spread. These include extensive road building, increased suburban development, and an expansion in the ranching industry" (Callihan 1993; WRIC 2003).With the aid of humans, by 1965, 767,000 hectares of California grazing land had been infested (Maddox 1985). Yellow starthistle is a pioneering plant that takes over disturbed regions of grassland and oak woodland (Maddox 1985). Because it germinates in the late fall, the species is able to out-compete grasses in disturbed areas using differential growth and root depth as a seedling to minimize interspecific interference (Sheley 1994). It also grows a deep taproot so it can continue to absorb moisture in dry years when rival plants suffer(Sheley 1994). Yellow starthistle is found in 209 countries, 23 states and as of 1993, it was estimated to take over 2400 hectares each year nationwide (Callihan 1993) Its distribution is considered cosmopolitan since it is found throughout the globe. In California, it is found in 56 of 58 counties. According to the CDFA, in 2003 only Mono and Imperial counties did not report any findings (CDFA 2003). An estimated 15-22% of the surface land of California is infested with the plant, making it the most widely distributed non-agricultural crop in the state (Benefield 2001). |  |
| Yellow starthistle is part of the
sunflower family (Asteraceae), which contains approximately 1100 genera and
25,000 species (Michaels 1991). Fossil records suggest the family may have
originated 30 million years ago, but other researchers believe Asteraceae date
back approximately 100 million years to the mid-Cretacaeous period (Michaels
1991). Likely originating in the northern portions of what is now South
America, the family experienced rapid diversification. "This
explosive radiation within the family has posed problems for attempts to resolve
phylogenetic relationships at higher taxonomic levels and to understand
character evolution" (Michaels 1991). Indeed, in the last 30 years,
eight different phylogenetic relationship designs have been developed for the
family. A morphological evaluation of the family conducted by Kare Bremer
in 1987 identified thirteen distinct tribes within the Asteraceae family, but
the genus Centaurea was not included in the study. The delineation of
these tribes has received critical review in subsequent studies (Michael
1991). A molecular study of the family headed by Helen Michaels in 1991
suggested one cause of the disagreement is an abundance of parallel and
convergent evolution within the family. The genus Centaurea includes
starthistle and knapweed species. It originates from Mediterranean Europe and
North Africa, but evidence of genus hybridization has been found
in south and central Europe (Maddox 1985).Across the United States,
Centaurea solstitialis exhibits variation in both phenology and morphology (Maddox 1985).
It has a long seed life,
an essential characteristic for weeds (Callihan 1993). Seeds were found to
survive six to ten years buried in soil (Callihan 1993).
Other Interesting Facts about Yellow Starthistle: Bibliography
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