What does Southern California have in common with central Chile and south Australia? They are three of only five small regions of the world that have what is termed a Mediterranean climate, UCLA Professor Philip Rundel said. That means mild, wet winters, dry summers and a wealth of biodiversity.

All five regions are part of a select group of 25 regions of the world "designated as key ecological hot spots," Rundel said. The five unique areas include the Mediterranean Basin of southern Europe and northern Africa; the Cape region of South Africa; and southwestern and south Australia. These spots are defined not only by climate, but by unique plant relationships, Rundel said.

California's unique status is attributable in part to geological forces that have contributed to the emergence of mountains and other topographical features that have allowed the diversity to flourish, Rundel said. And "dynamic fire cycles" are another natural component of change and renewal of the land.

Plant life

The Southern California region includes about 2,200 species of native plants, constituting nearly half the flora occurring anywhere within the state, he said. About one-fourth of them are rare, endangered or highly restricted in distribution, according to Rundel's guide, "Introduction to Plant Life in Southern California, Coast to Foothills."

The largest number of rare and endangered species in the U.S. outside of the Hawaiian Islands are in San Diego County, he said. Some of them are discussed in his text, but space limitations confined the book to only about 300 plant species, he said.

California is one of the 25 most significant areas in the world for biodiversity, Rundel said. And within California, San Diego County is the most diverse.

"The highest number of (flora) species occur there and nowhere else," Rundel said. "The Pacific Northwest is beautiful, but you see the same species over and over."

Rundel, a biology professor in the Department of Ecology and Evolutionary Biology at the University of California, embraces his subject with all the affection of a fifth-generation California native. His family moved to the state in 1850, he said.

Rundel, 62, has worked extensively in South Africa and Chile, and is also director of a research and teaching reserve called the Stunt Ranch Santa Monica Mountains Reserve, a 310-acre area open to university classes and docent tours for schoolchildren. The reserve, part of the state UC system, is open to the public by arrangement. Visit the Web site at http://nrs.ucop.edu for information.

After years of scientific and technical writing, Rundel wrote his pocket-sized book to help others share his view of the beauty of the land, laying the groundwork for their own love affair with nature.

"The UC press said we could have 250 pictures, and we squeezed them to get 320 in there," Rundel said. "A book is much more interesting if it has pictures."

Most of the photos were shot by photographer Robert Gustafson, a retired collections manager of the Botany Department of the Natural History Museum of Los Angeles County, according to his biography. Gustafson has been studying and photographing California flora for more than 30 years.

Change and renewal

Wide areas of San Diego County, in the third year of recovery from the Cedar and Paradise fires, are experiencing the natural post-fire recovery process that Rundel describes in his book.

"A lot of our biodiversity is hidden in the soil, and it only comes out after wildfire," he said. "The seeds of the annual species are stimulated after fire. There's a nitrogenous compound stimulated by ashes. The seeds can wait up to 100 years, sitting in the soil for the next fire."

The first year after a fire, beautiful flowers play an important role holding the nutrients in the soil that would otherwise be lost. Such flowers have evolved, because otherwise they would be under the canopies of the great trees and wouldn't survive, Rundel said.

"There are lots of plants that have these specialized niches," he said. "Like the desert plants that wait for that one rain in a century that make them germinate."

The flowers become fewer, and the short-lived plants fade. Then the shrubs return, he said. Deerweed, a key species, is one of the most common. A member of the legume family, it fixes nitrogen to the soil using bacteria in its root nodules. That's important to prevent the soil from being depleted, as other plants become re-established. Deerweed is also important as a food source for deer and other animals, as the land replenishes itself.

The mission

Rundel's field guide provides an ecological framework to learn about the state's abundant flora and fauna from the woodlands to the wetlands. It covers areas from Santa Barbara to the Channel Islands, and includes parks and other areas where the public can view "plant communities."

"All five Mediterranean areas have good wines and nice beaches," Rundel said. But people need to be aware that urban expansion poses a strong and continuing threat to regional biodiversity.

"We're on a mission to get people to see how unique our systems are," Rundel said.

Contact staff writer Agnes Diggs at (760) 740-3511 or adiggs@nctimes.com.