Eriochloa contracta

Prairie Cupgrass


Overview of Eriochloa contracta or Prairie Cupgrass

Stems and inflorescences of Eriochloa contracta, common name Prairie Cupgrass

 Roots of Prairie Cupgrass

Roots of Prairie Cupgrass are sparce as is typical of an annual grass.

 Closer View of Seedheads

The branches are short compared with other cupgrasses.

Branches Appressed to Rachis

The branches are usually appressed to the rachis, making Prairie Cupgrass appear spike-like.

 Inflorescence Sometimes Conceals Rachella

On the left, the hairy rachilla is concealed by the spikelets. On the right image an overturned branch shows the rachilla side.

 Close View Including the Rachis

Another view of the same branches. Can you see the tiny white dots at the base of each sspikelet?

Hairy Spikelets with White Dots at Base

These spikelets are hairy and have very short awns. There are white to purple spheres at the bases, the modified lower glumes.

 Spikelets

You can perhaps make out a couple of the thin white hairs below the short-awned apex of the spikelets.

 Close View of Bare Twig

The spikelets are stripped off. The branch and rachis are fuzzy and have a few long hairs.

How to Identify Prairie Cupgrass

  Eriochloa contracta is an annual bunchgrass. You can tell all the Eriochloa species by the tiny white or purple-black spheres just below the base of each spikelet (use hand lens). These spheres are cup-like but tightly surround the base of each spikelet. The inflorescence is strongly spike-like with branches appressed to the rachis. There are just a few long hairs on the pedicels. On the off chance that you succeed in seeing a mature caryopsis (the true seed deep inside each floret), it is minute, spherical, cola-brown, stripped, and shiny as glass.


Similar Species

  All the Echinochloa (Barnyard Grasses) and Urochloa (Signal Grasses) look a lot like cupgrasses (Eriochloa). Check the tiny white to purple dots of cupgrass as shown above. These are the modified lower glumes, which really are very spherical and stand out distinctly compared to those of Echinochloas and Urochloas. Beyond this, the challenge is to determine which of the five Arizona Eriochloas (cupgrasses) you have. This requires a microscope and disecting tools, so for purposes of this website you must settle for calling all of them "cupgrasses" or "Eriochloa". Most common in Arizona is Eriochloa acuminata, Southwestern Cupgrass.