Emex australis
Southern three-cornered jack
(c) Margaret Burger, some rights reserved (CC BY-SA) · licence
Family: Polygonaceae · Type: Herb · Not Native
Emex australis (Southern three-cornered jack) is a non-native California herb in the Polygonaceae family.
Southern three-cornered jack is a naturalized annual found in the Central Coast bioregion in coastal sandy areas at elevations below 200 meters. Flowering from May to December, this plant produces small, inconspicuous flowers with distinctive triangular fruit. Growing with stems 1 to 5 decimeters tall, it spreads across sandy ground with a sprawling habit. Its leaves have petioles 1 to 6 centimeters long, with blades 1 to 5 centimeters long and 0.5 to 3 centimeters wide. The fruit is particularly notable for its three-cornered shape, with each face bearing 3 to 4 elongated depressions and sharp spines 3.5 to 6 millimeters long.
Identification and appearance
Key characters: 1 sympatric species; key differentiators are plant size, fruit depression patterns, and spine length
Habitat and range
Habitat: Coastal, sandy areas
Elevation: < 200 m
Outside California: introduced in Hawaii, West Indies, Africa, Asia, Australia, native to southern Africa
Bloom period
Emex australis blooms May-Dec.
How to tell it apart
vs Rumex: Emex has fierce three-pronged spines on fruits; Rumex fruits have smooth papery wings.
Frequently asked questions
Is Emex australis native to California?
No. Emex australis is not native to California (recorded as not native).
When does Emex australis bloom?
Emex australis blooms May-Dec.
What plant family does Emex australis belong to?
Emex australis is in the Polygonaceae family, genus Emex.
What habitat does Emex australis grow in?
Emex australis grows in Coastal, sandy areas.
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.