The Channel Island of southern California are the home of some highly interesting and useful plants. Many of these are endemic to one or more islands, and many are suitable for the mainland home garden. First, a brief overview of the islands. They include (from south to north) San Clemente Island, Santa Catalina Island, San Nicholas Island, and five others that comprise Channel Islands National Park. See nps.gov/chis for info on the islands in the National Park.
Because of their separation from the mainland, the island species have evolved in unique ways. In the recent past (and to some extent in the present) these islands were subjected to military activities, grazing by livestock, hunting, tourist development (primarily on Catalina), and other human activities that have negatively affected their fragile ecology to varying degrees. Yet, they retain many of their important features and are receiving much better management today.
One of my favorite plants from the Channel Islands is Santa Cruz Island Ironwood (Lyonothamnus floribundus ssp. asplenifolius). Remarkably, it is in the rose family. It is fast growing to roughly 50 ft. in height with an upright form and not too much spread. Mine is in the back yard where it can provide some afternoon shade for the house in the summer.
It has large, compound leaves that look rather fern-like, and it produces huge clusters of white flowers in the Spring.
One of the many appealing features of this tree is its bark which resembles a redwood but peels off in long strips. This bark can look shaggy after awhile so you can either peel it off to clean it up or just leave it alone.
The amount of leaf drop is considerable so be prepared for that if you intend to plant one. I believe that the mulch provided by the fallen leaves is beneficial to the tree and to suitable understory plants, so I leave it all in place. When dry, the leaves crumble up nicely.
I think the best plants to have under the ironwood are other island natives. I have some Giant Coreopsis (Leptosyne gigantea) which is found on several of the islands, Santa Barbara Island liveforever (Dudleya traskiae), Santa Cruz Island Buckwheat (Eriogonum arborescens), and St. Catherine's Lace (Eriogonum giganteum).
In the photo above, the Dudleya traskiae is in the foreground and the Leptosyne gigantea is the funny looking thing on a woody stalk. The Leptosyne used to be included in the Coreopsis (sunflower) genus and it has typical sunflower flowers, but the taxonomists have recently moved it into a new genus. This plant grows only on the Channel Islands and a few spots on the mainland, primarily near the LA/Ventura County line. It wants to be very near the coast. In the summer it will lose all of its greenery and become a naked, somewhat sculptural stalk. When the winter rains come it will leaf out again and produce flowers. Mine have not flowered yet because they have only been in the ground a few months. They will next Spring. I love this plant because it reminds me of my visits to Anacapa Island.
The two buckwheats are shown below. First is St. Catherine's Lace, showing overall habit, leaves, and flower buds. The flowers have not opened yet (June 5) but should soon.
Next is Santa Cruz Island Buckwheat. This one really belongs where I have planted it because it is from the same island as the ironwood. I can easily imagine them growing together like this in some sheltered canyon on Santa Cruz Island.