Plants 12-57 cm. Stems basally swollen above tuberoid, 0.7-4.5 mm diam. distal to leaves; bracts 3-15. Leaves prostrate; blade 6-19 × 1-4.5 cm. Inflorescences ± densely flowered, 3.5-32 cm; rachis ± length of peduncle; bracts 3-12 mm. Flowers ± white with green or yellow-green midveins, fragrance nocturnal, strong, clovelike; sepals 2.5-4.5 × 1-2 mm; dorsal sepal projecting forward between petals, oblong to lanceolate; lateral sepals reflexed-spreading, obliquely oblong-lanceolate; petals reflexed-spreading, oblique to falcate, oblong, 2-5 × 1-2 mm; lip straight to ± deflexed, oblong to ovate-elliptic, 2.2-5.3 × 1-2.5 mm; spur ± horizontal, straight, 7-12 mm; viscidia oblong, 0.5-0.7 × 0.2-0.3 mm; rostellum blunt. Capsules 4-13 mm. Seeds cinnamon brown. 2n = 42. Flowering late May--Aug. Conifer and mixed evergreen forest, oak woodlands, chaparral; 0--2600 m; B.C.; Calif., Oreg., Wash. Piperia transversa is pollinated by geometrid moths (J. D. Ackerman 1977).