Sagina japonica is a perennial herb, stems very thin, prostrate to ascending to 10 cm long.
Leaves opposite, linear, 0.4-1 cm long, 0.1 cm wide, slightly succulent, bristle-tipped, fused at base across stem in a membranous cup (Flora of North America 1993+), basal rosette often present, also sometimes with short, leafy axillary shoots.
Flowers white (if petals present), petals 5 (sometimes 4 or none), shorter than sepals, sepals 4, to 0.25 cm long; flowers solitary or few, on glandular-hairy stalks in axils or tops of stems; blooming March-May.
Fruit a dry capsule rounded, to 0.3 cm long, cupped in old sepals, splitting open at top to release minute dark brown seed.
Wetland status: NL.
Frequency in NYC: Very infrequent.
Habitat: open waste sites, gravelly soil of roadsides, driveways, in dryish soil.