spiny sowthistle (Sonchus asper)
Sonchus asper (L.) Hill ssp. asper
Sonchus asper (L.) Hill ssp. glaucescens (Jord.) J. Ball
Sonchus nymanii Tineo & Guss.
CONFIRMATION STATUS: Pending confirmation.
TAXONOMY: The currently accepted scientific name for spiny sow-
thistle is Sonchus asper (L.) Hill.
NATIVE STATUS: Introduced, United States and Canada.
GENERAL BOTANICAL CHARACTERISTIS:
Habit: This annual plant is about 1–5' tall, branching sparingly in the up-
per half. The stems are dull green or reddish green, round, and smooth.
They have rather conspicuous longitudinal veins and are usually hairless,
although occasionally the upper stems and flowering stalks have a few
Leaves: The alternate leaves are up to 10" long and 3½" across, but more
commonly they are about half this size or less. On shorter plants, they are
rather crowded together on the stems, even where the composite flowers
occur. Depending on the local form of the plant, these leaves may be pin-
natifid, or they may lack significant lobes along the margins, in which case
they are broadly lanceolate or oblanceolate. The margins are conspicuous-
ly prickly, while the base of each leaf is auriculate with a pair of large
rounded basal lobes that strongly clasp the stem. The hairless leaves are
glabrous, and they tend to be folded upward along the central vein. How-
ever, there are no prickles along the central vein on the underside of each
leaf. Both the stems and the leaves contain a milky latex.
Flowers: The upper stems terminate in clusters of 1-5 composite flowers
on rather short stalks. Each flower is about 2/3" across when fully open,
and consists of numerous yellow ray florets. The base of each flower is
covered with dull green bracts and is rather short – only about 1/3" in
Fruit/Seeds: Each floret is replaced by an achene with a tuft of silky white
hairs. The achenes are flat, spindle-shaped, hairless, and have several long-
itudinal ribs. They are distributed by the wind.
Roots: The root system consists of a stout taproot.
REGENERATION PROCESS: Spiny sowthistle propogates itself by
HABITAT TYPES: Habitats include irregularly mowed lawns, edges of
yards and driveways, gardens, areas along roads and railroads, vacant lots,
barnyards, and waste areas. This species prefers highly disturbed areas,
and does not present an invasive threat to natural areas to any significant
degree. It is native to Eurasia and North Africa.
SITE CHARACTETRISTICS: Prickly sowthistle typically grows in full
sun, moist to slightly dry conditions, and different kinds of soil, including
loam, clay-loam, and shallow gravelly soil. The size of this plant is highly
variable, depending on the moisture and fertility of the soil. It can form
flowerheads very quickly during the summer.
SEASONAL DEVELOPMENT: The blooming period can occur from
late spring to early fall, and usually lasts about a month for a colony of
GENERAL DISTRIBUTION: Spiny sowthistle is found in all states and
provinces of United States and Canada (with the possible exception of the
SKY MEADOWS DISTRIBUTION: To be determined.
IMPORTANCE AND USES: There is insufficient information concern-
ing the floral-fauna relationships for this species. The composite flowers
probably attract various bees and Syrphid flies. The seeds of sow thistles
are a minor source of food to the eastern goldfinch. The foliage has a bitter
taste because of its milky latex, which may discourage its use as a food
source by mammalian herbivores to some extent.
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