Agricultural Services

An aggressive perennial thistle that spreads mainly through an extensive creeping root system. Originally introduced from Europe, it is the only thistle with separate male and female plants. Its roots spread both horizontally and vertically underground, allowing new shoots to continually replace older plants and form dense, long-lasting infestations. In riparian areas, it can reduce food sources and nesting habitat for wildlife.

Common tansy is a perennial forb that reproduces by both seed and short rhizomes (underground horizontal roots). Introduced from Europe in the 1600s, its pungently aromatic foliage has been used medicinally, as an insect repellant, and for embalming. Common tansy forms dense stands and the plants contain alkaloids that are toxic to both humans and livestock if consumed in large quantities. Cases of livestock poisoning are rare, though, because tansy is unpalatable to grazing animals.

Field scabious is native to Europe and was introduced as an ornamental plant. It is a tall perennial that favors grassy areas and develops a deep taproot. The flowers very closely resemble those of another ornamental perennial, Scabiosa (butterfly plant, pincushion flower) but each plant belongs to a different genus.

Perennial sow-thistle has long been an aggressive agricultural weed but can invade both natural and disturbed sites. It is a perennial plant that reproduces both by seed and creeping roots (rhizomes). Above-ground portions of mature plants die in winter and new shoots sprout from root buds in spring. Many native lettuces closely resemble perennial sow-thistle, but they either do not have the extensive root system or their flowers are a different color. Annual sow thistle is very similar but reproduces only by seed and its flowers are smaller. Native to western Asia and Europe and was probably introduced as a seed contaminant.

Scentless Chamomile can behave as an annual, biennial, or sometimes a perennial, but reproduces by seed only. Plants are usually very bushy and have a fibrous root system. It continually blooms, forms seeds, and seeds germinate throughout the growing season: fall seedlings overwinter and are usually first to flower in spring. Native to Europe, it was introduced as an ornamental and/or a contaminant in crop seed. This is not the chamomile used for tea as it is scentless. A single, robust plant can occupy one full square meter and produce up to one million seeds. Scentless Chamomile and Oxeye daisy are often mistaken for each other as the flowers are nearly identical, but the leaves are very different. Both plants are weeds – there are no native white-flowered daisies in Alberta. It can also be confused with stinking mayweed or pineapple weed, but the foliage of these two plants has an odor.

White cockle was introduced from Eurasia and is often confused with bladder campion (not hairy, not sticky) or night-flowering catchfly (hairy, upper stems sticky), white cockle is not sticky on any part of the plant. It is a short-lived perennial (sometimes biennial) native to Europe. Plants are either male or female, so not all plants produce seeds.

Brought from Europe over 100 years ago as an ornamental plant, Common toadflax has escaped and has now become a serious problem to rangeland and mountain meadows all over North America. This perennial plant makes seed, but reproduction is primarily by sprouting from its extensive, creeping root system (rhizomes); 2-3 week old seedlings can produce creeping roots. The ability of this plant to form large colonies allows it to crowd out other vegetation. Common toadflax is easily confused with Leafy spurge before flowering, but toadflax stems do not contain the milky latex that spurge does.

For more information on these Invasive Plant Species visit the Alberta Invasive Species Council.