Glumes about 5 mm long, long-pointed or with an awn 2 mm long or less. Cleistogamous seeds appear to remain within the leaf sheaths until disturbed or senesced culms fall to the ground. Often associated with alfalfa fields and nearby drainage ditches, dairies, and horse pastures. Cleistogamous seed develops within the leaf sheaths at the bases of plants in early summer and matures by late summer. Cleistogamous seed is hard-coated and can persist in the soil for at least 2 years.
Cultivation discourages survival, especially of seedlings.
However, native needlegrasses do not produce cleistogamous seed within the leaf sheaths at the bases of plants. In addition, native needlegrasses are not weedy and are unlikely to inhabit disturbed sites such as agricultural fields and dairies. It is native to Argentina, where it is a serious problem in alfalfa. It is believed to have arrived in contaminated alfalfa seed. Therefore, prevent new infestations by planting only certified alfalfa seed.