Milk thistle is described as an annual, winter annual, and biennial herb. It is an annual in its native range. The main stem is stout, ridged, and branching, and the overall plant size can range from two to six feet tall. A distinguishing characteristic of milk thistle is the white patches, or marbling found along the veins of the dark green leaves. The broad leaves are deeply lobed, and basal leaves can be 20 inches long and 10 inches wide. The leaf margins are yellow and tipped with woody spines 1/8" to 1/2" long. The leaves are alternate, and clasping to the stem. The stem leaves are smaller and not quite as lobed. Each stem ends in a solitary composite flower head, about two inches in diameter, consisting of purple disc flowers. The flower head of milk thistle differs from other thistles with the presence of broad leathery bracts that are also tipped with stiff spines,inch to two inches long. The seeds are heavy, inch long, flat, smooth, and shiny and the color ranges from black to brown mottled. The seeds do have a tuft of minutely barbed bristles, which is deciduous, and falls off in a ring when the seedsmature. |
