The Hawkweeds of the genus Hieracium have yellow or orange flowers that look like large dandelions, usually several in a cluster atop a stem above basal leaves or in some, alternate stem leaves. The Orange Hawkweed is an introduced invasive erect perennial that grows from 1/2 to 2 feet tall on hairy stems that contain a milky juice. Some hairs are glandular.
The leaves are usually basal only, 4 to 6 inches long (3 to 5+ times the width), numbering 3 to 8+, spatula to elongated lanceolate in shape, with no lobes or visible teeth, and very hairy on both sides.
The inflorescence is a compact cluster, somewhat in the shape of an umbel, with 3 to 7+ short-stalked flower heads. Stalks usually have glandular hairs.
The flowers are about 3/4 inch wide or less, composed of 25 to 120+ individual florets (typically 50 or fewer) that have corollas that are yellow at their base and opening into red to orange rays with 5 teeth on the squared off tips. The rays turn darker as they dry - to scarlet or purplish color. Styles are long with a bi-furcated tip. Around the outside of the flower head are 2 series of 13 to 30 green phyllaries that have pointed tips and hairy backsides, some hair glandular.
Seed: Fertile florets produce a dry columnar seed with small white bristles at the top. Seeds are wind and water dispersed. They are viable in the soil for up to 7 years.
Habitat: Orange Hawkweed grows from shallow fibrous and rhizomatous root system can rapidly colonize a newly disturbed area via runners. It is a plant of disturbed sunny sites; tolerates a variety of soils and moist to mesic water conditions.
Names: The genus name, Hieracium, is from the old Greek "hierakion" meaning 'hawk'. According to Pliny the Elder, hawks fed on the plant to improve their eyesight and from that comes the common name of Hawkweed. There have been numerous species delineated in the Hieracium genus over the years - 9,000 by one count. Many authorities, such as Flora of North America, believe there is no justification for such since many species of Hieracium reproduce from asexually produced seeds, which perpetuates populational and regional variants. The species name, aurantiacum, is from the Latin meaning 'orange-colored'. The author name for the plant classification, 'L.', refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: The native Hawkweeds in Minnesota and in North America differ from non-natives in that the natives do not produce runners, do not have basal leaf rosettes and have branched stems that have flowers in elongated clusters.
Above: The upper portion of the plant showing the flower cluster and the leafless stem. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: The flower corollas have yellow bases with orange throats, turning much darker when past pollination. Ray tips are squared off and toothed as are most Hawkweeds. Styles are long and exerted.
Below: Leaves are all basal, 3 to 5 times as long as wide.
Below: Leaves have hair on both surfaces with longer hair on the margin and the underside mid-vein. 1st photo - top side; 2nd photo - under surface.
Below: The stem, flower stalks, and flower calyx have dark hair, some glandular. The calyx has two series of pointed phyllaries with darker tips, all covered with hair.
Noxious Plant Notes: Orange Hawkweed is a non-native European species considered invasive by the Minnesota Department of Natural Resources, being listed on the "Secondary Noxious Weeds" list. It is most prevalent in NE Minnesota where it was first collected in St. Louis County in 1947. It is also the NE that it colors the roadsides from July onward. In North America it is found in most states of the U. S. except the drier SW and southern Central Plains. It is found throughout Canada except the 3 far north Provinces. Orange Hawkweed came to North America from Europe as an ornamental and was first introduced in Vermont in 1875. Some sources list an even earlier date of 1828, introduced as a herbal remedy.
There are nine species of Hieracium found in Minnesota, only 4 of which are considered native, the rest introduced. The natives are: H. scabrum, Sticky (or Rough) Hawkweed; H. longipilum, Hairy (or Long-bearded) Hawkweed; H. umbellatum, Narrow-leaf (or Rough) Hawkweed; and H. x floribundum, Smooth King-devil. The non-natives are: H. aurantiacum, Orange Hawkweed; H. caespitosum, Meadow Hawkweed; H. pilosella, Mouse-ear Hawkweed; H. piloselloides, King-devil Hawkweed; and H. vulgatum, Common Hawkweed.
The Garden census lists Canadian (or Yellow) Hawkweed, Hieracium canadense var. canadense as present in the Gardern, but as explained in the info sheet for that species, it is now considered part of H. umbellatum, the Rough, or Narrow-leaf Hawkweed.
The Minnesota DNR states that chemical control is best, using clopyralid or 2,4-D when the plant is in the rosette state. Home gardeners not having access to commercial products may have to apply several applications of weed killer before the root loses its reserves.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"