Originally printed in the Aug. 13, 2003 edition of the Illinois Valley News
Flowering plants, or Angiosperms, are primarily classified into families according to similarities in the flower structure. Leaves, stems and roots are also similar in members of the same family. Flower colors can be very different, even within the same genus. One of the largest and most abundant families is the Sunflower Family, or Compositae. Their flowers are composites of many small flowers clustered together into one head. In sunflower flowers only the outside flower in each head have a single yellow petal called a ray. The other flowers in the head have no petals but still can produce seeds. This pattern is in dandelions, asters, daisies and many others.
Thistles are also in the sunflower family, and their flower is a composite of many small flowers grouped together into one head. The purple hair-like petals come out of the top of a rounded base, or ovary. Each hair is considered a separate flower and produces a single seed which can be carried long distances in the wind, like dandelions. Artichokes are in this same group. The artichoke sold in stores is a composite flower which has not yet opened. The little hairs, inside on the heart that are usually discarded, would eventually extend out into the open. They would be purple and would be the same as a large thistle flower.
Knapweed is also part of the thistle group in the composites and have a similar but smaller flower. The outer flowers in the composite head are usually longer and more noticeable than the inner flowers, and there is a definite rounded ovary below the petals where the seeds are produced. Russian Knapweed is a common weed in our area , found along roadsides, power lines, cleared fields and other areas close to human activities. This is a clue that it is not a native plant but is called an alien. It is thought to have come from eastern Oregon and before that from the steppes of Russia. It competes very well with native plants and is hard to eradicate because of its deep tap root. It also survives burning, plowing, cattle grazing and even many herbicides. Russian Knapweed has purple flowers with a rounded speckled brown base. Scientists call it Centaurea repens. The word “centaurea” is used because of the idea that this is the plant of the Centaurs.
Star thistle is another alien invader from Eurasia by way of eastern Oregon. Most botanists think they arrived in western Oregon in bales of hay, because they appear first in pastures, near corrals, roadsides, or hunting camps in the mountains. Just a few years ago Star Thistle was the notorious invader that needed to eradicated before it became firmly established. Today it seems firmly established and is found in the same general areas as Russian Knapweed. Star Thistle has a yellow flower with long sharp spines arranged around the base of the petals. The scientific name is Centaurea solstitialis and is very closely related to knapweed.
The most recent invader in our area has received lots of attention and attempts to eradicate it seem to be futile. Spotted Knapweed, Centaurea maculosa, also has light purple to pink petals arranged above a rounded spotted base and it spreads very readily through the root system as well as wind carried seeds. All three plants compete very easily with native plants and are known to be toxic to horses.
There is a fourth member of this same noxious genus that is commonly sold in flower shops and in seed packets. Centaurea cyanus is usually called Bachelor’s Button and has a lovely blue flower. It is much more delicate and harder to establish than its relatives. However, don’t confuse it with Chicory, another alien weed from Eurasia, with coarse stems and spines but with a lovely blue flower.