Hieracium pilosella (Mouse-ear Hawkweed)

Plant Info
Also known as:
Genus:Hieracium
Family:Asteraceae (Aster)
Life cycle:perennial
Origin:Europe
Status:
  • Invasive - ERADICATE!
Habitat:part shade, sun; moist to dry sandy or rocky soil; roadsides, railroads, gravel pits, fields, lawns
Bloom season:June - September
Plant height:4 to 12 inches
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 7+petals

[photo of flowers] Usually a single flower, occasionally 2 or 3, at the tip of a hairy, leafless stem. Flowers are yellow, dandelion-like, ¾ to 1 inch across with up to 120 petals (ray flowers), the outer rays often with a red stripe on the back side.

[photo of bracts (phyllaries), hairy stem with 2 flowers and red stripe on rays] The bracts (phyllaries) surrounding the base of the flower are in 1 or 2 layers, lance-linear, tapering to a pointed tip, and densely covered in a mix of blackish glandular and non-glandular hairs and long, white, bristly hairs. Flower stalks are also covered in a mix of blackish glandular and non-glandular hairs, and long, white, bristly hairs.

Leaves and stems: Leaf attachment: basal Leaf type: simple

[photo of leaves] Leaves are all basal except for the occasional scale-like leaf along the flowering stem. Basal leaves are 1 to 4 inches long, 1/3 to ¾ inch wide, generally elliptic, widest at or above the middle, blunt or pointed at the tip, tapering to wedge-shaped at the base, and toothless. The upper surface is sparsely to moderately covered in spreading hairs 1/8 to ¼+ inch long, the lower surface is white from a dense covering of shorter, star-shaped hairs mixed with long, spreading hairs. Horizontal stems (stolons) are leafy and root at the nodes, creating dense colonies.

Fruit: Fruit type: seed with plume

Fruit is a dry seed with a tuft of light brown hairs to carry it off in the wind.

Notes:

A relative new-comer to Minnesota, Mouse-ear Hawkweed is much more widespread to our east and is definitely a weed to watch. According to the Global Invasive Species Database, in New Zealand it was a reasonably well-behaved introduction for about 80 years, then the population suddenly exploded. It sucks the life out of the soil and creates dense monocultures where nothing else will grow, even creating a “dead zone” of about 6 inches around its perimeter and expanding its territory more each year via both stolons and spreading rhizomes. In North America it is mostly found in the disturbed soils of roadsides, lawns and other places where weeds accumulate, but there are records of it in higher grade habitats of the Boundary Waters Canoe Area and Finland State Forest in Lake County. It is easily distinguished from other dandelion-like plants by the combination of the (usually) single flower, long, spreading hairs on leaves and stems, and glandular hairs at least on the upper stem and phyllaries.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken in Lake County.

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