Growth form: A bushy annual from 6” to 6’. Usually a little taller than wide with branches curving to produce an overall slightly spherical shape to the plant.
Roots: Russian thistle produces a fairly deep taproot, 1.5m, with a lateral width of 1.8m.
Stem: Stems are ridged and often have reddish hue to them.
Leaves:The young plants have long, ½ to 2”, thin, alternate leaves that drop off as the plant matures and are replaced by short awl-shaped leaves that are accompanied by sharp, pointed bracts.
Inflorescence/flowers: Male or bisexual flowers can be white, pink, red, purple, or even orange, in clusters at the base of leaves in upper branches. Flowers have no petals. 4-5 sepals with wing-like appendages and are persistent in fruit. Stamens extend beyond the sepals, exserted. They are wind pollinated and outcross or are self-fertile.
Fruit: Fruits are roughly spherical and are encased in the persistent sepals. Each contain a solitary seed that is spherical, slightly flattened or cone-shaped. The coiled embryo is visible through the translucent seed coat. An average plant can produce 2,000 seeds, a large plant can produce up to 100,000 seeds.
Similar species: See list of synonyms.
Life history: Annual.
Native/introduced: A non-native invasive plant considered noxious in most states. Original range includes eastern Russia and Mongolia. Thought to have arrived in the U.S. in shipments of flax seed about 100 years ago. Now a ubiquitous symbol of the American west.
Photosynthetic pathway: Phenology: Plants flower from early through late summer. When the seeds are mature the plant breaks from the roots at the crown and the whole plant is blown by the wind, tumbling and dispersing its seeds as it does.
Distribution: Found in every U.S. state except Florida. Usually associated with disturbed sites.