sheep sorrel

from The Century Dictionary.

• noun A plant, Rumex Acetosella, a slender weed with hastate leaves of an acid taste, abounding in poor dry soils. Also field-sorrel. See cut under Rumex.
• noun Species of Oxalis, more properly called wood-sorrel, especially O. Acetosella and O. violacea.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun small plant having pleasantly acid-tasting arrow-shaped leaves; common in dry places