Canada thistle
Cirsium arvense (L.) Scop.
Description from Invasive.org
- Appearance
- Cirsium arvense, a rhizomatous perennial grows from 1-5 ft. (0.3-1.5 m) tall. Roots can grow deep into the ground. Stems do not have conspicuous spines.
- Foliage
- Leaves are dark green and lanceolate to oblong-lanceolate. They are glabrous above, but their undersides have short, white hairs. They may be pinnatifid and very prickly. Basal leaves are 5-8 in. (12-20 cm) long. Leaves are usually sessile to slightly clasping. Leaf characteristics are variable across different varieties and subspecies.
- Flowers
- It has male and female plants. Female flowers are flask-shaped, 0.4-0.6 in. (1-1.5 cm) in diameter, and 0.4-0.75 in. (1-2 cm) tall. Female flowers are fragrant, the male flowers are not. Male flowers are smaller and more globose than the female flowers. Flowers range from purple to pink or white. It blooms from June to August.
- Fruit
- Fruits are tiny, 0.1 in. (2-3 mm) long, about 0.04 in. (1 mm) in diameter, with a white to light brown pappus.
- Ecological Threat
- Cirsium arvense is most commonly found in agricultural and disturbed sites, or sites that are undergoing restoration. It is shade intolerant and therefore is rarely found within wooded sites, except in clearings. It is found in some dry, sandy sites, but more commonly on the edges of wet habitats such as stream banks and lake shores. In the western and northern U.S. it presents a significant problem in prairie and riparian habitats.
Resources
- Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
- Weeds Gone Wild: Alien Plant Invaders of Natural Areas - Plant Conservation Alliance
- Element Stewardship Abstract - The Nature Conservancy
- Fire Effects Information System - USDA Forest Service
- Federal Noxious Weed Disseminules of the U.S. - USDA-APHIS
- Weed of the Week - USDA Forest Service
- Weed Field Guide - USDA Forest Service
- Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service
Selected Images from Invasive.org
View All Images at Invasive.org
Plant(s)
Peggy Greb, USDA Agricultural Research Service, Bugwood.org
Additional Resolutions & Image Usage
Peggy Greb, USDA Agricultural Research Service, Bugwood.org
Additional Resolutions & Image Usage
Seedling(s)
Ohio State Weed Lab , The Ohio State University, Bugwood.org
Additional Resolutions & Image Usage
Ohio State Weed Lab , The Ohio State University, Bugwood.org
Additional Resolutions & Image Usage
Seedling(s) with cotyledons
Ohio State Weed Lab , The Ohio State University, Bugwood.org
Additional Resolutions & Image Usage
Ohio State Weed Lab , The Ohio State University, Bugwood.org
Additional Resolutions & Image Usage
