Crabgrass is a collective term for a group of fast-growing, annual grasses that frequently invade lawns and gardens across the globe. This weed is a common source of frustration for anyone maintaining turf, as its rapid, coarse growth can quickly overshadow more desirable plant species. The name “crabgrass” is a direct, descriptive label given to the plant based entirely on how it spreads and grows.
The Physical Characteristics That Inspired the Name
The common name “crabgrass” stems from the plant’s distinct prostrate growth habit, which visually mimics the shape of a crab. From a central root system, the plant’s thick stems, or stolons, radiate horizontally outward along the ground surface. This radial spread creates a dense, low-growing clump.
The stems often hug the soil closely and can root down at the nodes, allowing the plant to creep outward and anchor itself firmly to the ground. This low-slung, spreading architecture makes it highly resistant to being cut by lawnmowers, enabling it to thrive in short-mown turf. Furthermore, the seed heads of the mature plant often branch out in a finger-like arrangement from the top of the stem, reinforcing the crustacean-themed imagery.
Identifying the Common Species
Crabgrass belongs to the genus Digitaria, a name derived from the Latin word digitus, meaning “finger,” which refers to the slender, spike-like seed heads. Two species are responsible for weed problems in lawns throughout North America: Large Crabgrass and Smooth Crabgrass. Distinguishing between these two types relies on observing specific textural and structural details.
Large Crabgrass, scientifically known as Digitaria sanguinalis, is characterized by the presence of prominent hairs. Stiff, perpendicular hairs cover both the leaf sheaths and the leaf blades, giving the plant a visibly rough or “hairy” texture. This species is generally the larger of the two, and its seed head typically consists of three to eleven spikes clustered near the top of the stem.
Smooth Crabgrass, or Digitaria ischaemum, is generally smaller and lacks the dense hairs found on its counterpart. While it is often described as hairless, closer inspection may reveal sparse hairs only located near the base of the leaf or at the collar region. Its seed head structure is also distinct, featuring fewer spikes, usually between two and six, that branch out in a similar finger-like arrangement.