Pilularia americana
American pillwort
Photo by Chez Brungraber
Family: Marsileaceae · Type: Herb · Native
Pilularia americana (American pillwort) is a native California herb in the Marsileaceae family, recognized by Only genus in water clover family (Marsileaceae) with simple rather than 4-parted leaves - represents ancient lineage.
American pillwort is a California native perennial found in northern Coast Ranges, Cascade Range, Sierra Nevada, Central Valley, Central Coast, San Francisco Bay Area, southern Coast Ranges, southern California, Transverse Ranges, Peninsular Ranges, and Modoc Plateau in vernal pools, mud flats, and lake margins at elevations below 2,000 meters. Lacking typical flowering information, this small aquatic plant grows as a low-profile green organism with leaves typically 2 to 6 centimeters long, occasionally reaching 11 centimeters. Growing with delicate, grass-like linear leaves emerging directly from the ground, it forms compact clusters in wet seasonal environments. Its leaves are slender and uniform, emerging in dense, low-growing clumps that spread across moist substrate. In wet habitats, the plant produces small round sporangium cases approximately 2 to 3 millimeters in diameter, supported by tiny stalks 1 to 3 millimeters long.
Identification and appearance
Key characters: Only genus in water clover family (Marsileaceae) with simple rather than 4-parted leaves - represents ancient lineage
Habitat and range
Habitat: Vernal pools, mud flats, lake margins
Elevation: < 2000 m
California counties: Riverside, San Diego, San Luis Obispo, Shasta, San Joaquin, Placer, Tulare, Ventura, Fresno, Lassen, Orange, Butte, Colusa, Contra Costa, Lake, Los Angeles, Madera, Mendocino, Merced, Modoc, Monterey, Sacramento, San Bernardino, Solano, Stanislaus, Marin, Yuba, Sutter, Glenn, Calaveras, Yolo, Santa Clara, Tehama, Alameda, Napa, Tuolumne, San Benito, Sierra, Sonoma, Santa Cruz, Santa Barbara
Outside California: Oregon, Baja California, also scattered central and southeastern United States, South America
How to tell it apart
vs Marsilea: Pilularia has simple grass-like blades, not Marsilea's distinctive four-part clover leaves.; vs Juncus: Look for the hard, round pill-like sporangium cases at leaf bases - rushes lack these.; vs Subularia: Pilularia leaves uncoil at tips like fiddleheads and have pill-like cases at the base.; vs Triglochin: Check for the spherical pill-like cases at leaf bases - arrow-grass lacks these structures.; vs Isoetes: Pilularia leaves uncoil from coiled tips; quillwort leaves emerge straight from a bulb-like base.
Frequently asked questions
Is Pilularia americana native to California?
Yes. Pilularia americana is native to California (recorded as native).
Where in California does Pilularia americana grow?
Pilularia americana occurs in Riverside, San Diego, San Luis Obispo, Shasta, San Joaquin, Placer, Tulare, Ventura and other counties, at elevations of < 2000 m.
What plant family does Pilularia americana belong to?
Pilularia americana is in the Marsileaceae family, genus Pilularia.
What habitat does Pilularia americana grow in?
Pilularia americana grows in Vernal pools, mud flats, lake margins.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.