Brodiaea santarosae
The Santa Rosa Basalt Brodiaea

Tom Chester, Wayne Armstrong and Kay Madore

Press Release, Tuesday, 13 November 2007

This summary for the press was updated on 30 November 2007 with the discovery on 27 November 2007 that one population lives on basalt soil that might be derived only from the basalt of the Santiago Peak Volcanics instead of the Santa Rosa Basalt.

A new rare species of Brodiaea has been discovered that lives only on only on basalt soils in areas currently or recently covered by the Santa Rosa Basalt of southwest Riverside County and immediately-adjacent San Diego County. The association with the basalt makes it likely that this is an ancient species, perhaps five million years old, which is on the verge of natural extinction in the near-geologic future when the last of the basalt is eroded away.

Because this species lives only on that basalt, scientists have named the species Brodiaea santarosae, the Santa Rosa Basalt Brodiaea. It has beautiful blue-purple lily-like flowers as large as two inches across, and blooms in May and June when the landscape is parched and dry, and most other grassland species have faded away.

The past history of this species, gleaned from the association with the basalt, is fascinating.

Prior to about ten million years ago, southern California was flat, without the mountains and faults present today, with a relief similar to that of eastern Kansas today. About ten million years ago, the North American Plate overrode an oceanic spreading center. In its dying gasp, the spreading center broke through the continental crust and completely covered that flat landscape with a series of lava flows, the Santa Rosa Basalt.

That cap of lava kept the land over which it spread together as the surrounding landscape was greatly altered to produce the mountains present today. That land remained essentially level as it was elevated, and is today called the Santa Rosa Plateau.

Five million years ago is an important date in the evolution of southern California species. Prior to that time, southern California received summer rainfall, and the species found here were not very different from species found elsewhere in North America. After that time, due to changes in atmospheric circulation caused by the new mountains such as the Sierra Nevada, we lost our summer rainfall and the climate became Mediterranean.

Species had to gradually adapt to the lack of summer rainfall, and the new habitat of the basalt was available to plant species that could grow there. (Many plant species cannot grow on basalt, since it is missing many normal plant nutrients and is high in minerals that are toxic to many plants.) Brodiaea santarosae may be an ancient species which colonized the basalt perhaps five million years ago and has survived as a distinct species to the present time due to its confinement to the basalt.

As more of the basalt has eroded, the populations of Brodiaea santarosae have become isolated. Further studies may be able to pin down when these populations were last in breeding contact, and give a firm estimate of the minimum age of this species.

B. santarosae is doomed to go extinct in the wild in the near geologic future (~100,000 years or so) unless it can adapt to non-basaltic soils, or unless viable populations are found to be present on basalt soil not derived from the Santa Rosa Basalt. At least 97% of the basalt has been eroded in the 8-11 million years since it formed. It will take much less than another 300,000 years (3% of the previous erosion interval) to erode the remaining basalt since the basalt has now been broken up into small areas and is now being eroded on all sides.

The story of how this species was finally recognized is also amazing. This species had been "hidden in plain sight", seen and even collected by previous botanists. Its true identity had gone undiscovered because the flowers of most Brodiaea species look very similar, all having nearly identical petals. It takes detailed examination of small aspects of the inner parts of the flowers to discriminate the species. This species was especially cryptic, since it has some flowers that superficially resemble another Brodiaea species, B. orcuttii; other flowers that superficially resemble a different Brodiaea species, B. filifolia, and yet other flowers that appear to be a hybrid between those two species!

The uncovering of this masquerade came from a fortuitous coincidence of events. Tom Chester and Wayne Armstrong had been working on Brodiaeas since 2003, and had begun to work on hybrids in 2005. Kay Madore had spent two years with Tom on his intensive work on the Flora of the Santa Rosa Plateau, gaining much experience with other Brodiaea species there, including B. filifolia. When Kay was doing routine botanical work in May for the Nature Conservancy, she came across some plants that were different from the Brodiaeas she had previously seen, and brought them to the attention of Tom and Wayne.

Tom and Wayne immediately began an intensive program to study the new plants, along with B. filifolia and B. orcuttii, both in the field and in the collections of herbaria in southern California. Thanks to their extensive previous work on Brodiaeas it did not take long to establish that these plants were a distinct species.

Interestingly, while it was clear from the beginning that the vast majority of specimens of B. santarosae grew on basalt, it appeared initially that a small number of specimens grew just outside mapped basalt areas. A perceptive comment, from one of the Madroño reviewers of the scientific paper, led to further field work in 2007 that revealed that all specimens in fact grew only on soils derived from basalt.

Quotes from the authors:

Comments from people not associated with this work:

This news release is based on a paper published in the latest issue of Madroño: A West American Journal of Botany 54:187-198 sent out in late October 2007. A 4 MB PDF copy of the article is available here.

More information about this species can be found at this website, which contains the figures from the paper, and most of the key points:

Pictures of this species, which blooms in May and June, are available here:

Higher-resolution versions of almost all of the pictures are available on request.

Pictures of the Santa Rosa Basalt are here:

Additional references on geological history and past climates of this area:

Brief biographies of authors:

Contact information for people mentioned above can be obtained from Tom Chester,, 760-723-0087.

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Copyright © 2007 by Tom Chester, Wayne Armstrong and Kay Madore.
Comments and feedback: Tom Chester
Last update: 30 November 2007