Hairy Crabgrass is an annual that usually is found growing with stems lying on the ground where they can root at the nodes. Stems (culms) can be 8 to 28 inches long.
Leaves: Leaf blades are 1 to 4 inches long and very narrow (3-8 mm), usually with hair on both surfaces that arises from small protuberances on the blade.
Sheaths and ligules: Leaf sheaths are open, usually have light hair similar to the leaf blades and are keeled (Like a boat). The ligules are short 0.5 to 2.6 mm.
The Inflorescence is a panicle with 4-13 spike-like primary branches which can be up to 12 inches long. Rarely do these primary branches subdivide. The rachis of the branches are flattened and winged, with tinges of red. The panicles will usually rise above the foliage and the foliage itself can be erect if not subject to cutting.
Spikelets: The individual spikelets are small (1.7 to 3mm long) and have hair on the margins of the glumes. They are arranged in unequally stalked pairs on the panicle branches. The lower glume is not veined, the upper glume is 3-veined, from 1/3 to 1/2 as long as the spikelets, and hairy on the margins. There are both upper and lower lemmas, the uppers yellow or gray, becoming brown when mature. The uppers are fertile while the lower are usually sterile, lacking paleas. Florets have 3 anthers. The mature panicle branches may sometimes be reddish or purplish. The grain is edible.
Habitat: Crabgrass is a weedy grass found in waste places, untilled fields and usually in lawns. It needs a sunny area, but soils may be moist to dry.
Names: The genus Digitaria is derived from the Latin digitus, meaning 'finger' which refers to the shape of the panicle branches of many of the species. The species name, sanguinalis, is derived from the Latin sanguis meaning 'blood', and probably referring to the reddish tinge of the panicle branch rachis. The author names for the plant classification are: First to classify was ('L.') which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was updated by ‘Scop.’ which refers to Giovanni Antonio Scopoli (1723-1788), Tyrolean naturalist who studied and published on plants, insects, animals and birds of the Tyrol. The genus Scopolia is named for him.
Comparisons: The closest comparative species of Digitaria found in Minnesota is D. ischaemum, the Smooth Crabgrass, where the panicle has only 2 to 7 spikelike branches, and the plant is only sparsely hairy, if at all. It is also an introduced species. The only other Digitaria species found in Minnesota is the native D. cognata, the Fall Witchgrass, which is a perennial, tufted grass, with erect stems, very narrow leaf blades, solitary spikelets, with veined lemmas.
Above: Crabgrass growing in an erect position. Photo ©Ted Bodner, USDA-NRCS Plants Database. Drawing courtesy USDA-NRCS PLANTS Database / Hitchcock, A.S. (rev. A. Chase). 1950. Manual of the grasses of the United States.
Below: Crabgrass in the usually found decumbent position of the stems, where rooting can take place at the nodes.
Below: 1st photo - The flowering seed panicle of Crabgrass with pairs of spikelets arranged along the spike-like branches of the panicle. Photo ©Robert W. Freckmann, University of Wisconsin. 2nd photo - spikelet detail, photo ©Anna Gardner, University of Iowa.
Below: Detail of the florets. Photo ©Anna Gardner, University of Iowa.
Hairy Crabgrass is a non-native Eurasian species that has now naturalized into all the lower Canadian provinces and all the lower 48 states except Florida. In Minnesota it is found in a number of counties in the southern half of the state, absent in the northern half, except perhaps in lawns. Of the 29 species of Digitaria found in North American, D. sanguinalis is one of the most common. Only 18 of the 29 species are native.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"