Properly called "broomrape". A parasitic weed. Broomrape is an obligate parasite on the roots of other plants which it attaches to, "stealing" water and nutrients from them. It can be identified by its 15-50 cm brownish stem, with small triangular leaves and yellow-white or pink flowers.
Some of the crop hosts of broomrape include lettuce and sunflower (Compositae), tobacco (Solanaceae), clover, peanut, and alfalfa (Leguminosae), and celery and carrot (Umbelliferae).
(Sources: Georgia Cooperative Pest Survey factsheet, Oregon Department of Agriculture)