Zannichelliapalustris – horned pondweed Distribution: Occurring on both sides of the Cascades crest in Washington; widely distributed throughout much of North America. Habitat: Fresh to brackish, standing to slow-flowing water, sea level to moderate elevations in the mountains.
Zeltneraexaltata – desert centaury, tall centaury Distribution: East of the Cascades in Washington; east to Nebraska and Colorado, south to eastern California. Habitat: Moist places, especially around alkaline lakes and hot springs.
Zeltneramuehlenbergii – Muhlenberg's centaury, Muhlenberg`s centaury Distribution: Occurring in scattered locations east of the Cascades crest in Washington; British Columbia south to California, east to Idaho. Habitat: Forest openings, wet areas at low to moderate elevations.
Zosteramarina – common eelgrass, seawrack Distribution: Widely distributed along the Washington coastline; Alaska south to California along the coast; also on the Atlantic Coast. Habitat: Sub-tidal area.
Zygophyllumfabago – Syrian bean-caper Distribution: Occurring east of the Cascades in Washington; Washington south to California, eastward in scattered localities to the Atlantic Coast. Habitat: Disturbed soil and wasteland.