Asteraceae, the daisy, sunflower, or composite family.
Plant: Erect, sometimes branching plant, 1'-6' high, with hollow stems, milky juice, prickly-spiny leaves, and loose clusters of yellow, dandelion-like flowers. Stems near the flowers often covered with sticky-tipped hairs, otherwise mostly smooth. Annual.
Flowers: Yellow, dandelion-like heads, about 1" across, consisting of all ray flowers. Involucral bracts narrow and pointed. Flowers in loose clusters (cymes).
Leaves: Alternate, with prickly-spiny margins, to about 10" long, clasping the stem, narrowly ovate to obovate in general outline, often pinnately lobed, but sometimes merely toothed, especially nearer the top of the plant.
Fruit: A head of achenes with silky hairs.
Habitat: Roadsides, waste areas.
This annual, introduced from Europe is similar to Common Sow-thistle
(S. oleraceus). It is distinguished by generally spinier leaves, and the presence of
reddish, sticky-tipped hairs on the upper stems below the flowers.
Where to find it:
Occasionally found in disturbed areas.
The common sow thistle in the park is Field Sow Thistle (S. arvensis), a perennial
with smoother leaves and sticky glandular hairs on the buds and bracts, but not on the stems.