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 plant known as Canada Hawkweed, H. canadense Michx. (or Yellow Hawkweed if you prefer) has very limited range and is currently treated as a subspecies of H. umbellatum, the Rough or Narrow-leaf Hawkweed. See the "names" section below for details.
The descriptive information presented here follows the treatment given by Flora of North America for H. umbellatum.
Stem: Rough Hawkweed is an erect native perennial growing to 5 feet in height on stems that are smooth and unbranched below the floral array but with much branching within the array. Within the array the stem is green to greenish-red. Stems contain a milky juice.
The leaves are alternate and located on the stem below the floral array. They are lanceolate (broadest in the lower half) to elliptical, stalkless; tips are pointed. The margins usually have small sharply pointed teeth, but irregularly spaced, sometimes giving the appearance of small lobes. The upper surface is a greenish gray, smooth, while the lower surface can be hairy and rough. Leaf edges do not have hair.
The floral array is composed of multiple loose branched clusters of stalked flower heads, mostly flat-topped, in which only one or two are open at a time and the more mature heads are positioned slightly below the immature heads. There are usually 5 to 30 heads but occasionally there may be fewer or many more.
Flowers: Each yellow flower head is about 1 inch wide, has 30 to 80+ bisexual and fertile florets with yellow corollas. The ray tips are truncated and have 5 tiny teeth. Disc florets are absent. The outside of the flower head has a series of very short floral bractlets (calyculi) that form on the flower stalk and then integrate into 12 to 21+ linear shaped phyllaries which have somewhat pointed tips.
Seed: Mature flowers produce a dry reddish-brown cypsela of columnar shape, 2.5 to 3.5 mm long with the pappus being bristle like hair for wind dispersion.
Habitat: Rough Hawkweed and related species grow in dry areas of woods, thickets, prairies, in more sandy type soils with mesic to dry moisture conditions, in full sun.
Names: The genus name Hieracium is from the old Greek "hierakion" meaning 'hawk'. According to Pliny the Elder, hawks fed on such plants 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. Thus many of these variants should be consolidated and H. canadense, H. kalmii and at least 22 others have been treated as one of the synonyms for H. umbellatum. The species name, umbellatum, means 'with an umbel' referring to the flower cluster type where all flower stems rise from the same point. That is not entirely the case here, but instead the head resembles an umbel. 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: 1st photo - The floral array typically has flowers of varying maturity. 2nd photo - The lower stem is reddish, alternate leaves. 3rd photo - The bractlets (calyculi - several visible on the stalk) and phyllaries of the flower head.
Below: 1st photo - Leaves have sharp irregularly spaced teeth. 2nd photo - Detail of leaf underside.
Below: Each flower head is about 1 inch wide, has 30 to 80+ fertile florets with yellow corollas. The ray tips are truncated with 5 tiny teeth.
Below: A mature seed head showing the bristle-like pappus for wind dispersion.
Notes: Eloise Butler had catalogued Rough Hawkweed in her plant index as present in the Garden area. She noted in her log on July 24, 1911 "Hieracium canadense.. in bud". She planted it in Sept. 1918, plants from Hazel Park in St. Paul. Martha Crone listed it on her 1951 Garden Census. It is fairly widespread in Minnesota with most absences being in the southern drier counties.
As far as the Minnesota plant lists from the DNR and the University of Minnesota are concerned 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 (Rough) Hawkweed; H. longipilum, Hairy (or Long-bearded) Hawkweed; H. umbellatum, Rough (Narrow-leaf) 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 formerly listed Canadian (or Yellow) Hawkweed, Hieracium canadense var. canadense as present in the Garden, but as explained above that species is considered part of H. umbellatum. H. aurantiacum is also in the Garden at times.
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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"