Canada thistle (Cirsium arvense)
Canada thistle (Cirsium arvense)
Canada thistle (Cirsium arvense)

Other common names
Californian thistle, Canadian thistle, Creeping thistle, Field thistle, Corn thistle, Perennial thistle

Description
Perennial, blooms midsummer. Leaves are wavy-margined to lobed, up to 6 inches long, and armed with yellowish spines. Small purple to white flowers are in clusters. The extensive, deep-seated root system spreads horizontally. Large seed production but low percentage of viable seeds.

...

Coltsfoot (Tussilago farfara)
Coltsfoot (Tussilago farfara)
Coltsfoot (Tussilago farfara)
Coltsfoot (Tussilago farfara)

Description
Perennial, flowers in April or early spring. Grows 4 to 8 inches. Bright yellow flowers similar to dandelions appear before leaves emerge. It has white, fluffy seed heads. Large, deep-green leaves develop later, often forming a complete canopy covering the soil. Top leaf surface has a smooth, almost waxy appearance, and the underside is covered with white, wool-like hairs. Leaf stems and larger leaf veins are distinctly purple in color. Spreads by...

Common bugloss (Anchusa officinalis)
Common bugloss (Anchusa officinalis)
Common bugloss (Anchusa officinalis)
Common bugloss (Anchusa officinalis)

Other common names
Common anchusa, Alkanet, Bee bread, Ox's tongue, Starflower, Common borage, Orchanet, Spanish bugloss, Enchusa, Lingua bovina, Blue bugloss

Description
Perennial herb, flowers May to October. Grows one to two feet tall. Stems and leaves are fleshy; overall plant is coarsely hairy. Basal leaves are narrowly oblong; mid-leaves are progressively smaller up the stem; and the upper leaves are sessile (no petiole) or...

Common cordgrass (Spartina anglica)
Common cordgrass (Spartina anglica)
Common cordgrass (Spartina anglica)
Common cordgrass (Spartina anglica)

Description
Perennial aquatic grass. Grows 1 to 4 feet tall. Leaf (blade) flat with margins loosely in-rolled at tip, 1/4 to 1/2 inches wide at base. Blade is at a 40- to 80-degree angle to the stem. Internodes are fleshy. Inflorescence is slightly open, with the branches loosely erect to ascending and loosely overlapping. Rhizomes are long and fleshy. It's similar to Dense-flowered cordgrass, Salt-meadow cordgrass and Smooth cordgrass. A detailed key is...

Common reed (Phragmites australis)
Common reed (Phragmites australis)
Common reed (Phragmites australis)
Common reed (Phragmites australis)

Other common names
Giant reed, Phragmites, Giant reedgrass, Roseau cane, Yellow cane

Description
A large, perennial, clonal grass species with creeping rhizomes and stolons and terminal, plume-like flowering stalks. This plant has woody, hollow stems that can grow 1 to 4 meters tall with stem diameters of 0.5 to 1.5 cm. Leaves are 15 to 40 cm long with an open leaf sheath. Common reed grows in a wide range of sites that hold shallow...

Creeping groundswell (Senecio angulatus)
Creeping groundswell (Senecio angulatus)

Description
Perennial shrub/herb. Dense, tangled shrub up to 6.5 feet tall. Will climb if suitable support is available. Leaves are glossy, thick, fleshy, and bluntly lobed. Often confused with Cape ivy but has thicker, diamond-shaped leaves. Yellow flowers are daisy-like with larger petals than Cape ivy. 

Impacts
Easily dispersed by wind-blown seed, stem fragments and dumped garden waste. This plant can smother existing native...

Creeping yellow cress (Rorippa sylvestris)
Creeping yellow cress (Rorippa sylvestris)
Creeping yellow cress (Rorippa sylvestris)

Other common names
Yellow fieldcress

Description
Perennial, flowers June to August. Grows up to 20 inches tall. Leaves are 2 to 4 inches long and pinnately divided into narrow, sharply toothed lobes. Flowers are yellow with four small petals.

Impacts
A common pest of Netherlands ormamental bulb-production areas. This plant can reduce bulb crop value and marketability as a contaminate of nursery stock...

Cutleaf teasel (Dipsacus laciniatus)
Cutleaf teasel (Dipsacus laciniatus)
Cutleaf teasel (Dipsacus laciniatus)

Other common names
Cut-leaved teasel

Description
Biennial, flowers July to September. Grows up to seven feet tall. Rosette leaves are ovid to oblong; mature leaves are opposite, large, oblong and prickly. Upper stem leaves are irregularly lobed. Stems are tall and prickly. Flowers are small, white and packed into ovate heads. Common teasel is similar, but it has purple flowers and no lobes on upper leaves.

Impacts...

Dalmatian toadflax (Linaria dalmatica)
Dalmatian toadflax (Linaria dalmatica)
Dalmatian toadflax (Linaria dalmatica)
Dalmatian toadflax (Linaria dalmatica)

Description
Perennial, blooms summer to fall. Grows two to three feet tall. Leaves are waxy, green, heart-shaped and one to three inches long. Flowers are one inch long and similar to snapdragons. Spreads both by seeds and creeping lateral roots.

Impacts
This deep-rooted perennial out-competes desirable forage plants for moisture and nutrients. Thrives in arid rangelands, pastures and railways.

Additional resources at...

Dense-flowered cordgrass (Spartina densiflora)
Dense-flowered cordgrass (Spartina densiflora)
Dense-flowered cordgrass (Spartina densiflora)

Description
Perennial aquatic grass. Grows 1 to 5 feet tall. Leaf (blade) margins are in-rolled, 1/8 to 1/3 inches wide at the base. Blade at a 15- to 35-degree angle to the stem. Internodes firm. The inflorescence is narrow, dense and cylindrical, with branches erect and overlapping. Rhizome is usually lacking or short and thick. Dense-flowered cordgrass is similar to Common cordgrass, Salt-meadow cordgrass and Smooth cordgrass. A detailed key is recommended for...