Phenotypic (Behavioral?) Plasticity in a Grass

I came across this grass that varies its growth pattern based on some unknown environmental cues.

When I first encountered it, it was growing on hard pavement, and both the stems and panicles were pressed completely flat against the ground. However, when later grown in more optimal conditions, the specimen adopted a much more upright position.

This behavior is quite fascinating, and might allow the species to occupy a wider range of environments than if it had a static phenotype.

Examination of the tiny spikelets seem to indicate it is of the genus Poa.