The single purple flowers of nodding thistle are 5-8 cm in diameter and grow at the end of long stems. The flowers are surrounded by broad spine-tipped bracts. At maturity, the flowers droop down or nod. The leaves are dark green, deeply lobed and have spiny edges. They are alternately arranged and can grow up to 15 cm long. Spiny wings cover the stem except just below the flowering head. Nodding thistle can grow up to 2.5 m tall.
Scentless chamomile has 12-20 mm wide flowers that have yellow centers surrounded by white petals. The leaves are very finely divided and are alternately arranged along the stem. Stems are highly branched and grow up to 30-60 cm. Sometimes the stems are reddish in colour.
The flowers of black henbane are very unique. They have united petals with 5 lobes. They are yellow with deep purple veins and throats and have a strong, unpleasant smell. The leaves are alternately arranged along the stem and are shallowly lobed with a wavy smooth edge. The entire plant is covered in sticky hairs. The fruit is typically urn-shaped with a crown-like edge. The stems are erect and grow up to 1 m tall.
Common tansy has unique yellow, button-like flowers that are arranged in dense, flat-topped clusters at the end of the stems. The leaves are deeply lobed or pinnate and alternately arrangement along the stem. Stems are round, often purplish-red, and dotted with glands. This plant can grow up to 5-150 cm high.
Among thistle species, Canada thistle has a characteristically small flower head that grows to a maximum of 1-2 cm wide. The flowers are typically purple and occasionally white. Although this species is quite prickly to the touch, the stem is actually smooth and has no spines or wings. One reason for its “success” as a weed is its capability to reproduce by seeds and by its creeping roots (rhizomes). Plants can regenerate from very small root pieces in the soil. It is probably the oldest regulated species in Alberta; the first legal document addressing weeds in our region was the 1865 Canada Thistle Act of Upper Canada.
Flowers have yellow centers surrounded by white petals. Single flower heads grow on the end of un-branched stems and are 12-20 mm wide. A key identifying characteristic of this species is that each plant has at least some oblong and spoon-shaped leaves with toothed edges. Ox-eye daisy stems grow 30-60 cm high and are typically hairless.
Perennial sow thistle has yellow, dandelion-like flowers that are grouped in loose clusters at the ends of stems. Flowers grow up to 5 cm wide. One plant may have up to 20 flower heads, but only a few are in bloom at one time. The leaves are lance-shaped or lobed, alternately arranged along the stem, and have a waxy appearance. The leaves have a prominent light green middle vein and spiny toothed edges. Stems are erect, leafy at the base, branched at the tops and grow from 10-120 cm high. Cut stems exude a milky juice.
Leafy spurge has green to yellow coloured flowers that have four crescent-shaped glands each. The linear leaves grow up to 5 mm wide and are often blue-green in colour. All parts of the plant release a white milky sap when injured. Leafy spurge grows 40-90 cm tall and has a creeping root system (rhizome).
The flowers have united petals that form an upper and a lower lip. The flower is mostly yellow with an orange centre on the lower lip. The flower also has a conspicuously long spur extending outwards from the base. The alternately arranged leaves are lance-shaped, oblong or linear, and often pale green or grey-green in colour. Stems are erect and grow up to 80 cm high. This plant reproduces by seeds and its creeping root system (rhizomes).
The 4-6 cm wide flowers of yellow clematis are bright yellow in colour and are often bell-shaped and drooping. The leaves are deeply lobed or pinnate and have 3-5 leaflets. Each fruit has a long hairy plume and several fruits are clustered at the end of each stem, forming a white hairy ball typical to the species. As a climber it grows on fences, posts, or other plants and can reach up to 4 m in height.