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Digitaria is a genus of about 300 species of grass (family Poaceae) native to tropical and warm temperate regions. Common names include crabgrass, finger-grass, and fonio. They are slender monocotyledonous annual and perennial lawn, pasture, and forage plants; some are often considered lawn pests. Digitus is the Latin word for "finger", and they are distinguished by the long, finger-like inflorescences they produce.
All crabgrasses have similar growth habits and flowering structures, but species are separated by minor differences in the flower structures and leaf pubescence. They typically have spreading stems with wide, flat leaf blades that lie on the ground with the tips ascending. The inflorescence is a panicle in which the spike-like branches are arranged in a digitate fashion. The spikelets are arranged in two rows on an angled or winged rachis. Each spikelet has two florets, only one of which is fertile. The first bracts at the base of the spikelets are either very minute or absent.
Crabgrass seed has a long germination period; if conditions are right, it can germinate throughout the growing season. Crabgrasses occur in tropical, subtropical, and temperate regions of both Hemispheres.
Though some crabgrasses are considered weeds, others have uses, especially as food. The seeds, most notably those of fonio, can be toasted and ground into a flour, which can be used to make porridge or fermented to make beer. Fonio has been widely used as a staple crop in parts of Africa. It also has decent nutrient qualities as a forage for cattle.
The prevalent species of Digitaria in North America are large crabgrass (D. sanguinalis), sometimes known as hairy crabgrass; and smooth crabgrass (D. ischaemum). These species often become problem weeds in lawns and gardens, growing especially well in thin lawns that are watered lightly, underfertilized, and poorly drained. They are annual plants, and one plant is capable of producing 150,000 seeds per season. The seeds germinate in the late spring and early summer and outcompete the domesticated lawn grasses, expanding outward in a circle up to 30 cm (12 inches) in diameter. In the autumn when the plants die they leave large voids in the lawn. The voids then become prime areas for the crabgrass seeds to germinate the following season.
Biological control is preferable over herbicide use on lawns, as crabgrass emergence is not the cause of poor lawn health but a symptom, and it will return annually if the lawn is not restored with fertilization and proper watering. Crabgrass is quickly outcompeted by healthy lawn grass because, as an annual plant, crabgrass dies off in autumn and needs open conditions for its germination the following spring.
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- "Genus: Digitaria Haller". Germplasm Resources Information Network. United States Department of Agriculture. 2007-10-05. Retrieved 2010-11-06.
- Vega, A. S. and Z. Rúgolo de Agrasar. (2001). Morphological interpretation of the spikelet in Digitaria atra (Poaceae: Panicoideae: Paniceae) and emended generic description. American Journal of Botany.
- "Digitaria". Integrated Taxonomic Information System. Retrieved 2010-11-06.
- "GRIN Species Records of Digitaria". Germplasm Resources Information Network. United States Department of Agriculture. Retrieved 2010-11-06.
- Gilani, S. S., et al. (2003). Taxonomic relationship of Digitaria in Pakistan. Pakistan Journal of Botany 35(3): 279–282.
- Gilani, S. S., et al. (2003). New subspecies of Digitaria sanguinalis from Pakistan. Pakistan Journal of Botany 35(3): 261–278.