Red (sheep) sorrel

Red sorrel, also called sheep sorrel (Rumex acetosella), is a low perennial broadleaf in the buckwheat family that first forms a basal rosette of distinctive arrowhead- or halberd-shaped leaves, each with two outward-pointing basal lobes that resemble small ears or dog-ears at the base of the blade. The leaves are smooth, somewhat fleshy, and have a sour, acidic taste. From the rosette, slender reddish flowering stalks rise, bearing tiny inconspicuous flowers that turn the seedheads a characteristic rusty reddish color in summer, often giving infested areas a reddish tinge. The arrowhead leaves with basal lobes and the reddish seedheads distinguish it from other low broadleaf weeds.

In turf, red sorrel forms patches of low rosettes and reddish flowering stalks that crowd thin grass and give infested areas a reddish, weedy cast, especially when the rusty seedheads develop in summer. Because it spreads by rhizomes, the colonies expand and persist, degrading uniformity and density, and its presence flags an underlying soil problem (low pH and fertility) that is itself limiting the desirable turf.

Red sorrel is a perennial that reproduces both by abundant seed and, importantly, by a shallow, horizontally spreading system of rhizomes (and creeping roots) that lets it form expanding colonies; the vegetative spread is its primary means of multiplication. Plants emerge from the rosette and send up flowering stalks in late spring and summer, producing large quantities of long-lived seed while the underground rhizomes simultaneously extend the patch, making established stands persistent and difficult to remove completely.

Red sorrel is a classic indicator of acidic, infertile, sandy, droughty, and poorly maintained soils, typically signaling low pH (often below 6) and low fertility. It invades neglected, thin, or under-fertilized turf, and the combination of acidic low-fertility soil and sparse grass gives both its seed and rhizomes the open, noncompetitive conditions they need to establish and spread outward.