Very few weeds have a root system comparable to this tenacious perennial. Sheep sorrel creeps and spreads by a maze of underground roots and rhizomes. Unless this plant is controlled when first observed, it can quickly choke and suffocate large areas of desirable turf. Sheep sorrel is most often associated with acid or "sour" soil, but it can thrive almost anywhere. Leaves are easily recognized by their unusual lance or arrow shape. They are narrow and thin during the spring, but by autumn they become broad and succulent. Another unusual characteristic of sheep sorrel is the method of flowering. The yellow-green flowers of the male are borne by one plant, while the reddish-brown flowers of the female are borne by a separate plant.