Capsella bursa pastoris is a hardy annual, (which often grows as a winter annual), is of European origin but is now naturalized around the world except in tropical climates. Shepherd's purse does its best in sunny, moist to dry, rich, disturbed soil, but it will also grow in partly shaded, extremely poor soils. One of the reasons for this is that the plant has sticky seeds, to which tiny insects get stuck, providing the seedling with extra food. Shepherd's purse has a slender, flexible, slightly hairy, white taproot, from which arises a basal rosette quite similar to that of a dandelion (Taraxacum officinale). The rosette generally grows to be 4" to 8" in diameter. The basal leaves are stalked, and the first leaves are usually rounded, while the later leaves are usually deeply toothed but may be rather variable. Smaller, slightly toothed, alternate leaves clasp the flowerstalk, which generally reaches 6" to 18" in height. The white flowers appear in clusters at the top of the stalk. The flowers are only about 2 mm across. Like all Brassicaceae flowers, they have 4 petals which form a cross and 6 stamens. The flowers are self fertilizing. As the first flowers are maturing, the stalk continues to grow and produce new flowers. Shepherd's purse can be found in flower from early spring through early winter. Each flower develops into a heart-shaped, two-celled seedpod, about 5 mm long, containing a number of tiny seeds. When the pod dries, it splits in half, releasing the mature seeds.
Capsella bursa-pastoris (Shepherd's Purse) - Kingdom: Plantae, http://www.kingdomplantae.net/shepherdsPurse.php (accessed January 23, 2017).