Orange hawkweed (Hieracium aurantiacum)

Orange flowers of a dense patch of orange hawkweed.

 
 

Orange hawkweed was introduced to the U.S. as an ornamental plant for its flame-colored flowers. It invades northern moist pastures, forest openings, abandoned fields, clearcuts and roadsides. Hawkweed colonizes quickly and can rapidly dominate a site, leading to a loss of native plant diversity.

Description

Appearance

Herbaceous plant that can grow 10-24 inches tall. Leaves are arranged in a basal rosette, from which a leafless flower stalk emerges. Flowers are orange to yellow.

Leaves and Stem

Hairy leaves are arranged in a low-growing basal rosette. Leaves are spatula-shaped, usually without teeth or with very tiny teeth, and are 4-6 inches long. They are dark green on the top and lighter green beneath. Each rosette usually produces one hairy stem, which holds 5 to 30 flower heads. Stems are covered with short, stiff, black hairs. Both stems and leaves contain a milky sap that is exuded when damaged.

Flowers

Flowers are bright red-orange to yellow, arranged in clusters of five or more at the top of leafless flower stalks. The dandelion-like flowers are 0.5-0.75 inches in diameter and have rectangular petals. Flowers bloom from June to September.

Seeds

Each flower holds 12-30 tiny, columnar seeds with a light-brown tuft of bristles for wind dispersal, similar to dandelions. Seeds also have tiny barbs that allow them to stick to hair, fur, clothing and vehicles. Seeds can also be dispersed by water, by "hitch-hiking" on animals or clothing, and are often moved in contaminated soil associated with transplanting new plants into gardens. Seeds are viable in the soil for up to seven years.

Rhizomes and Roots

Orange hawkweed has shallow, fine, branched roots. It spreads primarily vegetatively via aboveground runners (4-12 per flowering plant), as well as underground stems called rhizomes that produce new plants, and sporadic root buds.

Biology

Orange hawkweed is a perennial herbaceous plant that invades northern moist pastures, forest openings, abandoned fields, clearcuts and roadsides. It prefers full sun or partial shade and well-drained, sandy soils. Hawkweed colonizes quickly and can rapidly dominate a site.

Origin and Spread

Orange hawkweed is native to Europe. It was introduced to the U.S. as an ornamental plant for its flame-colored flowers. Its greatest density occurs on recently disturbed sites, as it is an early successional plant. In Minnesota, its largest distribution is in the northeastern part of the state. Visit EDDMapS to see current distribution map of orange hawkweed.

Don't be fooled by these look-alikes

  • Sticky hawkweed, Hieracium scabrum (native) - has leaves all the way up the stem, does not produce stolons, yellow flowers
  • Narrow-leaf hawkweed, Hieracium umbellatum (native) - has leaves all the way up the flower stems, leaves have sharp-toothed edges, yellow flowers
  • Meadow hawkweed, Hieracium caespitosum (non-native) - yellow flowers
  • Glaucous king-devil, Hieracium piloselloides (non-native) - does not have stolons, yellow flowers
 
Regulatory Classification

This species is not regulated. Orange hawkweed has been assessed through the Minnesota Department of Agriculture's noxious weed regulation evaluation process. In the assessment document, it was recommended that it not be regulated because it is so widely distributed, however the impacts of the plants were documented and people may choose to not plant orange hawkweed or to manage it where it is found.

Threat to Minnesota
  • Orange hawkweed colonizes rapidly and forms a solid mat of rosettes. This can lead to a loss of native plant diversity.
  • Orange hawkweed may produce chemicals that decrease growth of neighboring plants (allelopathic).
  • It is an aggressive competitor for space, light and soil nutrients. Under ideal conditions, one plant can cover an area 2-3 feet in diameter in its first year of growth.
What you should do

One way that invasive plant seeds and fragments can spread is in soil.  Sometimes plants are planted purposefully.  You can prevent the spread of invasive plants.

PlayCleanGo: Stop Invasive Species in Your Tracks

  • REMOVE plants, animals & mud from boots, gear, pets & vehicle.
  • CLEAN your gear before entering & leaving the recreation site.
  • STAY on designated roads & trails.
  • PLANT non-invasive species.
Native Substitutes
 
Control Methods

Mechanical control can be done by hand pulling or digging up small infestations. Dig deeply to remove belowground rhizomes and fibrous roots. Mowing reduces seed production, but encourages vegetative spread.

Herbicide control is most effective when spraying clopyralid or 2,4-D on the plant in the rosette stage (before the plant flowers). A surfactant should be added to the mix to ensure the herbicide will stick to the hairy leaf. These herbicides are systemic herbicides, meaning they are taken up by plants and move within the plant, which can kill leaves, stems, and roots.

Reporting
This species is unregulated, but if you'd like to add to the public information about this species you can report new occurrences by submitting a report through EDDMapS Midwest.
Resources