Three-awn Grasses (Aristida spp.)
These grasses are distinct in that each spikelet of the inflorescence has three awns (stiff hairs at the end). Several of these can be seen clearly in the image at left, in which the three awns appear as a triple-set of threads, running out from one common end.
This image below may help clarify the pattern -- here you see three spikelets, plus a fourth beginning to emerge (at the left); each of the emerged spikelets has three awns radiating out from near its tip. Different species of Three-awn have different lengths of these awns; the Poverty Three-awn (A. divaricata) has awns whose length is similar to the diagram below, while some of the others have much longer awns relative to the length of the seed.
Sometimes the triple character of the flower is not so obvious, however A number of kinds of three-awn grasses are scattered around our Saguaro Juniper area, and they are not very easy for non-experts to distinguish. These include the following:
Poverty Threeawn (Aristida diverticata)
Mesa Threeawn (A. hamulosa)
Harvard Threeawn (A. barbarata)
Spidergrass (A. ternipes) Two of the awns are much reduced in this species.
These four (above) Three-Awns are warm season perennial grasses.
Purple (and Red) Threeawn (A. purpurea -- two varieties)
This type of Three-Awn grows in small, dense clumps, and grows in cool as well as in warm seasons. When growing, it has purple to red seedheads.