perennial sowthistle
Family
AsteraceaeScientific Name
Sonchus arvensisOther Common Names:
gutweed swine sowthistle
field sowthistle
corn sowthistle
Habit
Seedlings have 0.2-0.3 inches long by 0.1-0.2 inches wide, ovate cotyledons. Mature plants have a vast horizontal root system and hollow, succulent, branching stems reaching 7 ft tall.
Leaves
Found mostly on the lower half of the stem, leaves are lance-shaped 2.5-16 in long and alternate in arrangement. Lower leaves have winged curled back stalks and are deeply lobed with soft prickly margins. Stalkless upper leaves clasp the stem and have 2-7 backward pointing lobes on each side. Margins of upper leaves are not as deeply lobed but they have teeth tipped with spines.
Identifying Characteristics
Yellow flower heads measuring more than 1 in across, stems below and flower bracts covered with yellow hairs and milky juice in stems and leaves. Even small numbers of plants can severely reduce crop yields due to its ability to compete for light, space, nutrients, and moisture.
Flower Seed Head
Each plant bears several flower heads made up of bright yellow ray florets and dark-green floral bracts. Stems below flower heads and floral bracts are covered with yellow hairs.
Seed Fruit
A single seeded achene. The seeds 3.0 mm long and less than 1 mm wide are reddish brown, and rectangular. Each plant is capable of producing 4,000 seeds that may remain viable in the soil for several years. Dispersal is aided by the pappus made up of several 0.4-0.5 in long white hairs.
Where Found
Throughout Canada and the United States in cultivated crops, pastures, and meadows.
Growth Habit
upright and nonwoody
Thorns or Spines
present
Approximate Flower Diameter
Varies:
quarter,
half dollar,
larger
Dominant Flower Color
Varies:
yellow,
orange
Flower Symmetry
radial symmetery
Leaf Hairs
Varies:
has hairs,
no hairs
Leaf Shape
Varies:
lance,
oval
Leaf Arrangement
Varies:
alternate,
rosette
Leaf Margin
Varies:
lobed,
serrated
Leaf Structure
simple
Leaf Stalk
Varies:
none,
shorter than leaf
Stem Hairs
Varies:
has hairs,
no hairs
Stem Cross Section
round or oval
Milky Sap
present
Root Structure
taproot
Life Cycle
perennial
Ochrea
not present
Plant Type
Herb