Deinandra is a genus of annual and perennial flowering plants in the tribe Madieae, family Asteraceae (the daisy family), order Asterales. The genus belongs to a group of plants commonly called tarweeds — a name reflecting the sticky, resinous glands that cover their stems and leaves and produce a characteristic pungent odor, particularly strong in warm conditions.
The genus is not universally recognized as distinct: many taxonomic authorities treat its species within the broader genus Hemizonia, and the boundary between the two has shifted repeatedly. Plants in Deinandra are mostly annual herbs, typically bearing yellow ray and disc florets arranged in small heads. The glandular hairs that give tarweeds their common name serve as an adaptation to dry-summer Mediterranean climates, helping to reduce water loss and deter herbivores.
Deinandra is native to the Western United States — primarily California, with species also found in Arizona — and extends into northwest Mexico, including Baja California and Baja California Sur. The approximately 20 recognized species occupy a range of habitats across this region, from coastal grasslands and chaparral slopes to desert margins and island outcrops. Several species have very restricted ranges and are considered rare; Deinandra minthornii, for example, is listed as a rare species by both the State of California and the California Native Plant Society.
Notable members of the genus include Deinandra fasciculata (clustered tarweed), widespread through southern California and Baja California; Deinandra mohavensis (Mojave tarweed), found across inland Southern California counties; and Deinandra bacigalupii (Livermore tarweed), restricted to Alameda County.
Distribution
Deinandra species are native to the Western United States, with the majority concentrated in California; the range also includes Arizona and extends south into northwest Mexico (Baja California and Baja California Sur). Individual species vary from broadly distributed across the state to highly localized single-county endemics.
Taxonomy Notes
Deinandra is placed in the tribe Madieae within Asteraceae and is not universally accepted as a genus distinct from Hemizonia. Many taxonomic treatments, including some major flora works, subsume Deinandra into Hemizonia, making the genus boundaries dependent on the authority followed.
Ecology
Tarweeds in the genus Deinandra are adapted to the dry-summer Mediterranean climate of California and northwestern Mexico. Their glandular, resinous stems and leaves reduce desiccation and deter herbivory, allowing them to remain active and bloom through the hot, dry summer months when most co-occurring annuals have set seed. They are characteristic plants of grasslands, disturbed roadsides, chaparral margins, and coastal scrub.
