- perennial with prostrate stems
- leaves opposite, long and narrow, with ruffled margins
- flowers in small axillary clusters, with 5-lobed greenish-yellow corolla
- milky sap present in all parts of plant
- narrow range: Starr and Zapata counties and northern Tamaulipas
- grows in shallow sand or sandy loam, sometimes on graded roadsides and other disturbed areas
