A Guide to the Best of Southern California : TREKS : Desert Flower Beside the Sea

AS SAN DIEGO’S largest wildflower puts on a spectacular show this month, it delivers a message that global warming is nothing new. From late March into May, the Mojave yucca blooms in Torrey Pines State Reserve amid other plants from the dry inland desert--a magical sight to behold in the seaside Mediterranean climate. You can spot the Mojave yucca by its sword-shape leaves edged by curling fibers. In spring, it thrusts out an intricate maroon bud spike that swells into a luxuriant stalk of creamy, bell-shape blossoms.

Like many a city resident, this yucca is an in-migrant. We know from the fossil record that it came from afar to join the rare Torrey pine. Both are residents of the reserve because plants move--that is, their range expands or shrinks as climate changes. The pines remain from the last ice age, until perhaps 10,000 years ago, a cool, moist era when forests blanketed the California coast and its offshore islands. The Mojave yucca remains from the next climatic episode, a worldwide warming from about 8,000 to 3,000 years ago, at which time hot winds decimated coastal forests in all but a few spots like San Diego, which were kept mild by the sea. Wind-borne seeds impelled desert plants to the future site of San Diego. Six species remain today, with the yucca the star of the group. Will these survivors have new meaning if another global warming is indeed on the way?