Weed Information: Hieracium caespitosum (hawkweed, yellow)
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Hieracium caespitosum (hawkweed, yellow)

Family: Asteraceae

Description

Yellow hawkweed is one of the worst pasture weeds in the New England states. It spreads by rhizomes, stolons, and seeds. The leaves are very hairy on both surfaces. The flower stalks are 1 to 3 feet tall, and the outsides of the flower heads are covered with black glands. In the Pacific Northwest there are also two common native hawkweeds which are similar to yellow hawkweed. These are Hieracium canadense and Hieracium umbellatum. They can be distinguished by the fact that the basal leaves are smaller than the middle stem leaves while Hieracium pratense is the opposite.

Characteristics

Flower Color
  • Yellow
Inflorescence Type (How the flowers are arranged on the plant)
  • Corymb
  • Cyme (simple or branched)
  • Head
  • Simple umbel
Number of Petals
  • 5 petals
  • more than 10 petals
Petal Separation
  • Completely free to base
  • United > 75% of length
Petal Tip
  • Square
  • Toothed
Flower Symmetry
  • Flowers regular
Flower Length (Head length in the Asteraceae)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
  • 8 mm (.32 inch)
  • 9 mm (.36 inch)
  • 1.0 cm (.40 inch)
  • 1.5 cm (.6 inch)
Flower Width (Head width in the Asteraceae)
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
  • 8 mm (.32 inch)
  • 9 mm (.36 inch)
  • 1.0 cm (.40 inch)
  • 1.5 cm (.60 inch)
Number of Sepals
  • sepals lacking
  • more than 10 sepals
Sepal Separation
  • Completely free to base
Sepal Tip
  • Pointed
Flower Sex
  • Bisexual (perfect)
Number of Styles
  • 1 style
Number of Stamens
  • 5 stamens
Stamens Attached to the Petals
  • Stamens attached to the petals
Stamens Connate (united)
  • Anthers united, syngynoecious

Carpel Separation
  • Carpels united (or one)
Number of Carpels
  • 1 carpel
Ovary Position
  • Inferior (epigynous)
Fruit Type
  • Achene
Fruit Length at Maturity
  • 1 mm (.04 inch) or less
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
Fruit Width at Maturity
  • 1 mm (.04 inch) or less
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • All basal
  • Alternate
Leaf Type
  • Simple (including lobed leaves)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Pinnate
Petiole (leaf stem) Blade Ratio
  • Petiole absent (leaf sessile)
  • Petiole < 25% total length
Leaf Length (blade PLUS petiole)
  • 2 - 4 cm (.80 - 1.60 inches)
  • 4 - 10 cm (1.60 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
Leaf Width
  • 1 - 2 cm (.40 - .80 inch)
  • 2 - 4 cm (.80 - 1.6 inches)
Leaf Shape (simple leaves only)
  • Lanceolate
  • Oblanceolate
  • Oblong
Leaf or Leaflet Margin
  • Entire
  • Serrate
  • Ciliate
Leaf or Leaflet Blade Base
  • Acuminate (attenuate)
  • Clasping
Leaf or Leaflet Tip
  • Acute
  • Rounded (obtuse)
Leaf or Leaflet Blade Surface
  • Floccose
  • Hirsute
  • Hispid or setose
  • Lower leaf surface more hairy
  • Strigose
Succulence
  • Not succulent

Milky Juice
  • Juice milky
Woodiness
  • Herbaceous
Spines or Thorns
  • Spines or Thorns ABSENT
Aromatic (vegetative structures)
  • Not aromatic
Life Cycle
  • Perennial
Growth Habit (while flowering)
  • Spreading ascending
  • Erect, columnar (narrow)
Plant Height at Maturity
  • 2 - 4 dm (8.0 - 16.0 inches)
  • 4 - 6 dm (1.3 - 2.0 feet)
  • 6 - 8 dm (2.0 - 2.6 feet)
  • 8 - 10 dm (2.6 - 3.3 feet)
Wind Dissemination
  • Fruit, seed, or spore wind borne
Moisture Regime
  • Seasonally saturated
  • Mesic
Chlorophyll
  • Present

Stem Cross Section
  • Round
Flowering Stem Leaves
  • Stem leafless
  • Stem leaves greatly reduced
Main Stem Branches
  • Main stem unbranched

Root or Vegetative Propagule
  • Rhizomatous
  • Rooting at the nodes
  • Stoloniferous

US State
  • Connecticut
  • Delaware
  • Georgia
  • Illinois
  • Kentucky
  • Massachusetts
  • Maine
  • Michigan
  • North Carolina
  • New Hampshire
  • New Jersey
  • New York
  • Ohio
  • Pennsylvania
  • South Carolina
  • Tennessee
  • Virginia
  • Wisconsin
  • West Virginia
  • Indiana
  • Maryland
  • Rhode Island
  • Vermont
  • Idaho
  • Minnesota
  • Montana
  • Oregon
  • Washington
  • Wyoming
Canadian Province or Territory
  • British Columbia
  • New Brunswick
  • Nova Scotia
  • Ontario
  • Prince Edward Island
  • Quebec
  • Newfoundland
Other
  • District of Columbia
  • St. Pierre and Miquelon

  • How to Know the Weeds, 1972, (ISBN# 0-697-04880-2) See page: 158
  • Northwest Weeds, 1990 (ISBN 0-87842-249-8) See page: 154
  • Ontario Weeds, 1992 Agdex 640, Publication #505 See page: 246
  • Weeds, 1955 (1980) Walter Conrad Muenscher, ISBN# 0-8014-1266-8 See page: 476, 477
  • Weeds of California and other Western States, 2007 (ISBN 13: 978-1-879906-69-3) See Page: 345
  • Weeds of the Midwestern United States & Central Canada, University of Georgia 2010, ISBN#0-8203-3506-1 See page: 108
  • Weeds of the North Central States, 1981 Univ. of Illinois, Urbana - Champaign Bulletin # 772, See page: 220
  • Weeds of the Northeast, 1956, Univ. of Delaware Field Manual #1 See species #: 106
  • Weeds of the Northeast, 1997 Cornell University ISBN# 0-8014-8334-4 See page: 148
  • Weeds of the Northern United States and Canada, 1964 Montgomery See page: 195
  • Weeds of the Northern U.S, and Canada, 1999 Royer and Dickinson, (ISBN# 1-55105-221-0) See page: 41
  • Weeds of the United States and Their Control, Lorenzi 1987, ISBN# 0-442-25884-4 See page: 318
  • Weeds of the West, 1992 (ISBN 0941570-13-4) See page: 143
  • Weeds of the West, 2000 (ISBN 0941570-13-4) See page: 145
  • Wildly Successful Plants, A Handbook of North American Weeds, 1977 (ISBN# 0-02-528850-4) See page: 23, 133
  • Listed as a `Weed` by the Biota of North America Program, 2008 x
  • Listed in the WSSA Composite List of Weeds X
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