Tall swamp onion is an interesting and fairly attractive perennial wildflower. The scape is stout but flattened in cross-section, rising 40-80 cm from a cluster of bulbs on a short rootstock. The 3-6 leaves are flattened or channeled, and range from 4-12 mm wide and usually shorter than the scape (See photo at right.).
The 2-4 bracts are united at the base and subtend the many-flowered umbel. The individual bracts are membranous, broadly ovate in outline, and 5-7 nerved. The umbel consists of 15-30 flowers. Each flower contains 6 rose-purple tepals from 6-10 mm long. Each tepal is lanceolate in outline with acuminate tips. The stamens surpass the perianth. The anthers are purple or yellowish. The ovary is crestless. The style is exserted with a capitate stigma. The pedicels are thin and from 10-18 mm long.
Tall swamp onion may be found in wet meadows and in swampy soils from medium to high elevations in the mountains.
Tall swamp onion may be found in the Cascade Mts. from southern British Columbia south to northern California and hence further south in the Sierra Nevada Mts. to Sequoia National Park. It is also found in the Coast Range from southwestern Oregon to northwestern California. It is also found east of the Cascades in mountainous areas from eastern Oregon to western Idaho and northeastern Nevada.