Ecology/Biology:

C. arvense is an invasive weed in North America and tends to crowd out native species reducing biodiversity in a number of communities. C. arvense can only establish from seeds on open ground since its early development is highly sensitive to light conditions (10, 12). However the seeds of C. arvense have a long dormancy period and can survive in the soil for up to 12 years (3). Thus, it can lie dormant long enough until a fire or other disturbance that reduces vegetative cover gives it the chance to grow. C. arvense is a dioecous, obligate outcrosser that is pollinated predominately by bumblebees (12). However, it mainly propagates itself by vegetative reproduction since its sexual reproduction is inherently inefficient (4). Seeds tend to loose their pappus before being dispersed, abortion rates of the seeds tend to be high (due to genetic loads from obligate-outcrossing), and populations of C. arvense tend to be predominately female (13, 4). However, roots contain numerous buds that can grow true stems and develop new plants and thus allows C. arvense to increase its biomass in an area with great efficiency (4). The roots of C. arvense grow at a rate of 1 cm per day spreading horizontally by 1.2-1.5 m and vertically by 1.8m within two years (9, 10). New plants can grow from any part of the root and thus makes C. arvense hard to eradicate.

Distribution:

C. arvense is a perennial, dioecious herb that is native to Europe, Asia, and North Africa ( 5). It was transported to North America by contaminated seed in the 17th century (5). C. arvense has a wide distribution in North America and is classified as a highly noxious weed under Utah seed law section 4-17-3 (1). C. arvense mainly occurs on disturbed sites such as on roadsides, fields, irrigation ditches, and industrial areas; however, in Utah it also invades Oak brush and aspen communities at elevations of 1280 to 2535m (13, 5, 10, 11). Two ecotypes of C. arvense persist in Utah and can be distinguished by their leaves.

Charateristics

Stems:	Upright growth to a height of 30-200cm (2).
Roots:	Formed from buds on underground roots and are highly dense, descending to depths of 1.8m (2, 10, 9). Roots grow horizontally for about 6 feet before descending vertically (7).
Leaves:	Basal leaves are deciduous, with fine hairs on the top surface and woolly hairs on the underside of the leaf (2). The leaves of var. horridum are 3-15 cm wide and deeply lobed with an oblong, oblanceloate, or elliptic-obovate shape while var. mite has lobe-less leaves (2, 13).The leaves are spiny at the margins (2).
Flowers	Arranged in a corymbose inflorescence located at the ends of the stems (2). The flowers are purple or white in color and the achenes are various shades of brown (2, 13).
Seeds:	The seeds are attached to a pappus that allow dispersal of the seed to other sites (2, 13).

Control Methods:

Control methods range from the use of herbicide, planting competitive speices such as alfalfa or certain grasses, digging up the roots repeatedly at certain times during its growth, and by the introduction of various beetles and nematodes that feed or in some way damage C. arvense’s shoots, roots, or leaves (6).

Plant Ecology Class

Link to References