How patient are Scotch thistle seeds?
By Chelsie Vandaveer
March 6, 2003
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killerPlants Tendrils: ~~1~~2~~3~~4~~5~~
Suggested Reading: Click here.
Scotch thistle (Onopordum acanthium Linnaeus) is native to Eurasia. It is well armed; the leaves and phyllaries (bracts below the flowerhead) have spines, the stem has spined alae (wings, leaf-like tissues). The unwary browser is quickly
educated by the plant.
It is thought the thistle was introduced to North America in the late 1800s, although Henry David Thoreau mentions Scotch thistle in his journal in 1840. "Cannot a man be as calmly tolerant as a potato field in the sun, whose equanimity is not disturbed by Scotch thistles over the wall...?" (Journal of H.D. Thoreau, June 22, 1840, Peregrine Smith Books)
Scotch thistle either did not arrived in Utah or simply went unnoticed until 1963. In eight years, it spread over 22,540 hectares (55,674 acres). Since then, it has 'won' the noxious weed award in twelve states. (USDA Natural Resources Conservation Service, Plant Profiles)
Scotch thistle is a biennial. The seeds germinate in late autumn and the plant rests through its first winter. In spring it forms a rosette of leaves that stay close to the ground while the plant builds its taproot. The following spring, Scotch thistle bolts (sends up its flowering stem), produces seed, and dies. Should the seeds germinate a few weeks earlier, in late summer, the plant behaves as an annual--produces seeds and dies about a year later.
According to the California Department of Food and Agriculture, a Scotch thistle produces on average 20,000 to 40,000 seeds each in its own achene with a pappus (modified petals that become a 'parachute' for wind dispersal). The seeds will not germinate until rains have washed away an inhibitor and they receive cycles of light and dark.
If the seeds become buried, they will wait until something disturbs the soil enough to bring them to the surface. Patient, they are; the buried seeds remain viable for seven to twenty years. (Onopordum genus, Weed Information, CDFA)
The California Department of Food and Agriculture has photographs of Onopordum acanthium to help people learn to identify it. To view the photographs, click on the link:
http://www.cdfa.ca.gov/phpps/ipc/weedinfo/onopordum-acanthium.htm
Click on the thumbnails to enlarge the images.
Series: | 1 | | 2 |
killerPlants Tendrils: ~~1~~2~~3~~4~~5~~
Suggested Reading:
Purple Thistle (Cirsium horridulum) Plant of the Week - April 12, 2004
What is an artichoke? Weird Plants - January 22, 2004
What toxic resin was used on skin? Herbal Folklore - June 9, 2003
What is the cosmopolite? Renfield's Garden - April 30, 2003
Why must the tumbleweed tumble? Weird Plants - June 27, 2002
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