Digitaria sanguinalis (L.) Scop
summer grass, crab grass
This is an annual grass (living for 1 season only) with long (up to 1m) sprawling stems. As with all grasses it has fibrous roots. The many soft stems grow close to the ground in an open space or will push up through other grasses when crowded. The stems when they are close to the ground will often produce roots at the nodes (elbows along the stems). Stems are variable in colour from green to purple, as are the ligules. Ligules are the small appendage seen at the base of the leaf when the leaf is pulled back from the stem. The ligule on this grass is a membrane 1-2mm long.
Leaves are soft and smooth, usually hairy near the base, 4-8 mm wide and with an open hairy sheath around the stem.
Inflorescence (flower or seed head) is formed by 3-13 spikes growing from a slender upright stem. Spikelets (buds/flowers/seeds) are flat and in pairs. Fertile floret (flower) is pale grey or slightly purple in colour and has mauve coloured filaments and anthers.
This grass is commonly found in lawns, gardens and disturbed areas. It is easily removed by releasing the roots with a knife or trowel, however care must be taken that the sprawling stems are also removed. When they have rooted into the ground the stem will often break off when the central part of the plant is being removed.
Other plants easily confused with this plant
Digitaria sanguinalis (summer grass) and Digitaria ciliaris (also called crabgrass and summer grass) are both introduced plants in NSW, they are very similar and you would require a micoscope and some seed for a positive identification.
Eleusine indica (crowsfoot grass) may also be confused with these Digitarias, however, Eulsine does not root at the nodes, has fewer hairs on leaves and sheath, fewer spikes and has ligule of a membrane with hairs. The appearance of the inflorescence is more clumped (less spreading). Spikes or branches are shorter and the spiklets (buds/flowers/seeds) are in 2 rows but along only 1 side of the spike or branch.
A native grass, Digitaria parviflora (smallflower finger grass), may also be confused. Digitaria parviflora is easily distinguished as it is mostly hairless, whereas the other Digitaria's are very hairy especially at the base of the plant. The seed spikes are also smaller.
All of the above flower in Summer and sometimes into Autumn.
Sources & References
"Weeds - an illustrated botanical guide to weeds of Australia" by B. A. Auld and R. W. Medd
"Plantnet FloraOnline" (2005) http://plantnet.rbgsyd.nsw.gov.au/
Prepared by Justin KY Chu, July 2005
Checked and updated by IEWF, March 2006