Romneya Harv., the Matilija poppy, is a genus in the family of Papaveraceae which is sometimes seen as monotypic, when the second species R. trichocalyx is reduced to a variety of R. coulteri. Both plants are native to California and bordering areas of Mexico. They are a rather common topic on the PBS list, including the question whether they fall into the geophyte scope or not. California authorities consider them shrubs or perennials and California wiki editors do not believe they belong on the wiki. To quote Dylan Hannon from the pbs list: "Romneya is a perennial with a branched, brittle crown and deep-growing, rather slender perennial roots. The stems are also perennial and green and may be leafy through the dry season." Once established in adverse conditions outside of where they are found in nature they are able to retreat to their extensive root system. They can travel several meters underground, coming up in places far from where they were planted and reach 2.5 meters (8.2 feet) in one season. Even when not in flower, the silvery leaves provide interest to the garden.
Matilija poppies are one of those plants many people struggle to establish, even in California in locations where others grow them successfully. In hot climates it is necessary to plant them in fall, after the heat of summer, to give them time to build up a root system. Quite surprisingly, they are perfectly hardy down to USDA zone 7 or maybe lower, moving their dormant time to winter, and making a spring planting mandatory. In any case, they might take 2-3 years to flower. On the other hand it's not unheard of them to send up shoots aggressively in a radius of several meters once they are happy. Substrate is another field of debate - there have been reports of thriving plants in both heavy clay and gravelly ground, and failures in both types, so water management seems to be the key aspect.
While there are climates where Romneya can be evergreen, it is most of the time better to cut them down to the ground both for looks and vigor of the new shoots.
Romneya coulteri Harv., the more common of both species, is a impressive solitary perennial with big white flowers, reaching 15-20 cm across. It grows in dry canyons in chaparral and coastal sage scrub plant communities, sometimes in areas recently burned. Despite being a Californian native, the seemingly ephemeral flowers cope well with summer rain in Martin Bohnet's German garden, where they flower in mid summer.
