Calyptridium monospermum, synonym Cistanthe monosperma, is a perennial plant in the miner's lettuce family (Montiaceae), known by the common name one-seeded pussypaws.

It is native to western North America from Oregon to Baja California, where it grows in a number of habitat types, including forest and woodland.

It grows somewhat upright, the plant approaching half a meter in maximum length.

C. monospermum usually has more than one inflorescence per basal rosette; the related C. umbellatum generally has only one.

The four petals on each flower are white to pink, and are surrounded closely by round, frilly sepals.