Hibiscus trionum
Flower-of-an-hour
(c) Tony Rebelo, some rights reserved (CC BY-SA) · licence
Family: Malvaceae · Type: Herb · Not Native
Hibiscus trionum (Flower-of-an-hour) is a non-native California herb in the Malvaceae family, recognized by size, habitat, and flower color.
Flower-of-an-hour is a naturalized annual found in California's Central Valley and Foothills in disturbed places at elevations generally below 350 meters. Flowering from April to November, this plant produces delicate yellow flowers with a distinctive purple-black base, each bloom approximately 2 centimeters wide. Growing with erect stems 30 to 60 centimeters tall that can develop prostrate branches, it has a bristly texture. Its leaves are roughly 5 centimeters long, deeply 3 to 5-lobed, with coarsely toothed edges and stellate hairs on the underside. The fruit is enclosed within an inflated, papery calyx, measuring 1.5 to 2 centimeters long.
Identification and appearance
Key characters: 1 sympatric species - distinguished by size, habitat, and flower color
Habitat and range
Habitat: Uncommon. Disturbed places
Elevation: generally < 350(1450) m
Outside California: native to Europe, central Africa
Bloom period
Hibiscus trionum blooms Apr-Nov.
How to tell it apart
vs Malva: Hibiscus has 5-12 bracts and 5-branched style; Malva has 3 bracts and numerous style branches (as many as fruit segments).; vs Rosa: Hibiscus has a central column of fused stamens and 5-branched style; Rosa has separate stamens radiating from center.; vs Rhododendron: Hibiscus has fused stamens forming a central tube; Rhododendron has 5-10 separate stamens and woody stems.; vs Alyogyne: Hibiscus has bracts separate to base; Alyogyne bracts are fused into a cup around the flower base.; vs Pandorea: Hibiscus has a column of fused stamens; Pandorea is a woody vine with tubular flowers and paired opposite leaves.
Frequently asked questions
Is Hibiscus trionum native to California?
No. Hibiscus trionum is not native to California (recorded as not native).
When does Hibiscus trionum bloom?
Hibiscus trionum blooms Apr-Nov.
What plant family does Hibiscus trionum belong to?
Hibiscus trionum is in the Malvaceae family, genus Hibiscus.
What habitat does Hibiscus trionum grow in?
Hibiscus trionum grows in Uncommon. Disturbed places.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · 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.