Description - from Wikipedia

Aristida adscensionis is a species of grass known by the common name sixweeks threeawn. It is native to the Americas but it is distributed nearly worldwide. It grows easily in disturbed and waste areas and has potential to become a weed.

Description
This annual bunchgrass is quite variable in appearance, its size and shape determined largely by environmental conditions. It grows in a tuft to heights between 5 and 80 centimeters. It forms a narrow inflorescence of spikelets, each fruit with three awns.

References
External links
Jepson Manual Treatment
USDA Plants Profile
Grass Manual Treatment
Kew GrassBase
Aristida adscensionis in West African plants – A Photo Guide.