Perennial sow thistle (Sonchus arvensis)
Appearance: Perennial herbaceous plant, 2 - 5' tall erect, single stem, branches near the top into several flower stalks. Broken stems emit a sticky milky bitter juice with a sour odor.
Leaves: Alternate, lower leaves are deeply lobed, upper leaves clasp the stem; similar to dandelion leaves except with teeth ending in small weak prickles.
Flowers: Bright yellow up to 2" wide daisies, blooming from June through August.
Seeds: Tufted, dispersed by the wind.
Roots: Widely spreading white brittle roots penetrating five to ten feet, producing new plants from small root pieces.