Romneya coulteri, the Coulter's Matilija poppy or California tree poppy, is a perennial species of flowering plant in the poppy family. Native to southern California and Baja California, it grows in dry canyons in chaparral and coastal sage scrub plant communities, sometimes in areas recently burned. It is a popular ornamental plant, kept for its large, showy flowers.
This is a shrub which may exceed 2 m (7 ft) in height, its woody stem growing from a network of rhizomes. The gray-green, waxy-textured leaves are each divided into a few lance-shaped lobes, the blades growing up to 20 centimeters (7.8 in) long. The inflorescence is a large, solitary flower with six crinkly white petals each up to 10 cm (4 in) long. At the center of the flower is a cluster of many yellow stamens. The fruit is a bristly capsule, 3–4 cm (1–2 in) long, containing many tiny seeds.
While beautiful, this plant often grows aggressively once planted. It spread clonally by underground rhizomes and can pop up several feet away from the original plant.  Naturally, such a plant cannot be placed anywhere in a garden.
This plant bears the largest flowers of any species native to California, rivaled only by Hibiscus lasiocarpos. It was nominated for the honor of California state flower in 1890, but the California poppy won the title in a landslide.
- "Romneya coulteri". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 22 October 2015.
- California Native Plant Society Rare Plant Profile
- Harrison, Lorraine (2012). RHS Latin for gardeners. United Kingdom: Mitchell Beazley. p. 224. ISBN 9781845337315.
- "Wildflowers, NPS, SAMO NRA - Romneya coulteri detail page". www.smmflowers.org. Retrieved 2017-06-16.
- Flora of North America
- Clark, C. Genus Eschscholzia: History
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- Pink, A. (2004). Gardening for the Million. Project Gutenberg Literary Archive Foundation.
- Jepson Manual Treatment
- USDA Plants Profile
- Photo gallery
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