An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
PRICKLY LETTUCE-Lactuca serriola L.
DESCRIPTION-Stiff erect annual, winter annual, or biennial with milky juice, from a large taproot, reproducing only by seeds. There is 1 stiff, principal stem, often hollow, branching only in the flowering part, or sometimes with a few short branches from the base, smooth above, but usually with sharp prickles on the lower part, 2 to 6 feet high.
The leaves are alternate, bluish green, stalkless, tightly clasping the stem with 2 angled or earlike lobes. The lower leaves are 2 to 10 inches long, and are of 2 forms. The margins may be cut into deep irregular lobes, or they may be unlobed, as in the common var. integrata Gren & Godr. Both types often have prickles along the margins, the large white midvein, and the other veins on the lower leaf surface. The upper stem leaves are all smaller, unlobed, and similar to the second type of lower leaves. Seeding leaves are unlobed, and form a basal rosette at the ground level.
There are many yellowish flower heads, 1/8 to 1/3 inch broad, composed entirely of petallike ray flowers. The flower heads are on short stalks, and are borne at the top of the plant on many branched flowering stems. Each flower head produces 6 to 30 achenes.
The achenes are eggshaped, flattened, about l/8 inch long or less, light gray, with 5 to 7 parallel ridges on each side, short-bristly near the summit, and a very slender beak arising from the broad end, which bears a tuft of fine white hairs. The hairs drop off quickly.
DISTRIBUTION-Prickly lettuce is an introduced European weed. It grows in any type of disturbed soil. It is a serious pest in irrigated crops, especially in those which are not weeded regularly, as grain and alfalfa fields, orchards, and vineyards. Also common along roadsides, yards, and gardens. Widespread throughout the state; from 100 to about 8,000 feet elevation; flowering May to October.
Copyright (c) 1972 The Arizona Board of Regents