A larger-than-life grasslands profile offers an unusual venue to study the serpentine soil complex and explore the foundation of Edgewood’s unique biota. Set against a painted mural, the exhibit tells the above-ground story in terms of the below-ground structure, revealing the geologic composition (iron-magnesium silicates) that created Edgewood’s unique soils. The community of serpentine grassland plants, including blow-wives, blue dicks, large-fruited lomatium, California plantain, goldfields, and serpentine linanthus, is magnified to 20 times life size. Can you spot three life phases of the Bay checkerspot butterfly?
In this Exhibit
The Bay checkerspot butterfly is a threatened species that lived at Edgewood until 2002. This butterfly is endemic (native and confined) to serpentine-derived soil. The primary host plants for Bay checkerspot larvae are California plantain and, later in the season, purple owl’s clover. The Bay checkerspot butterfly has a wing span of about 2 inches (5 cm). Since 2007 there has been an ongoing program to reintroduce the Bay checkerspot butterfly to Edgewood, along with habitat restoration to remove the exotic plants that crowd out the butterfly’s food source plants.
Bay checkerspot larvae emerge from eggs in early spring. The tiny caterpillars feast on California plantain and grow quickly. Some may move to other food plants such as purple owl’s clover. As the food plants die off in late spring, the caterpillars stop eating and survive the dry summer in a resting state, known as diapause. They remain in this state, in shallow cracks in the dried earth, until the plantain germinates following fall rains. The caterpillars resume eating, form pupae in early spring and later emerge as adult butterflies.
Blow-wives are unusual because they are easily missed when in full bloom, but hard to ignore when fully in fruit. They don’t “open” until ready to deploy seeds, then produce a showy round head. Each ripe seed is equipped with shiny white scales that create a propeller-like parachute that catches the wind. If you find one of the seeds on the ground near the plant, pick it up and let it drop to watch it twirl to the ground—or catch and ride the wind. Blow-wives bloom from April to May in Edgewood’s grasslands.
From March to May, blue dicks provide bright spots of blue in Edgewood grasslands, chaparral, and open woodlands. This herbaceous perennial sprouts from a bulb (corm) with two or three grass-like leaves and a tall flower stalk. The flower stalk can reach to two feet tall with a tight cluster of blue/violet flowers at the end of the stalk. Flower color can vary from deep violet to white.
Each of the five lomatiums that grow in Edgewood have flat-topped clusters of many tiny, cream-colored flowers that provide landing pads and nectar for adult butterflies. Except for California lomatium, which grows to 4 ft. in dappled shade, these members of the Carrot family are all low-growing perennials in the serpentine grasslands. Large-fruited lomatium (Lomatium macrocarpum) is the most common lomatium in the preserve, and it flowers in early spring. By mid spring, you’ll see this plant holding up its flattened, winged fruits along the upper Clarkia trail and Ridgeview trail.
California plantain grows low to the ground, with long fuzzy leaves at its base and upright stems that terminate in groups of small white flowers. California plantain blooms at Edgewood from March to June in serpentine grasslands. This plant is critical caterpillar food for the Bay checkerspot butterfly. Female Bay checkerspot butterflies lay clusters of eggs at the base of California plantain so that the newly-hatched caterpillars will have quick access to food.
At Edgewood, which is relatively dry, goldfields do not get much taller than 3 inches. Goldfields is in the Sunflower family (also known as the Daisy or Aster family). In this family, what appears to be a single flower is actually a collection (bouquet) of many small flowers. In a goldfields flower, the central area is a cluster of yellow star-like disk flowers encircled by a fringe of yellow ray flowers. One blooming goldfields may be inconspicuous; however, when hundreds bloom at the same time, goldfields form a spectacular golden-yellow carpet in the serpentine grassland. Along with lomatiums and tidy-tips, goldfields provide nectar for adult Bay checkerspot butterflies.
Serpentine linanthus is a small annual that blooms from March to June. Its flowers have five petals, ranging in color from blue to purple to pink, at the end of a tube. As its name suggests, serpentine linanthus will only grow on serpentine soil. It can be found most easily on the Edgewood Trail between Canada Road and I-280.
Serpentinite is a weathered metamorphic rock brought to the surface at Edgewood through seismic activity along the San Andreas fault. Serpentinite has a gray, mottled appearance a bit like snake skin. Soil derived from this rock contains heavy metals, like nickel and chromium, that can be toxic to plants, along with low levels of nitrogen, calcium, and other nutrients that plants usually need to grow. However, a number of plants have managed to adapt to this soil and thrive–as evidenced by the profusion of flowers that bloom in Edgewood’s serpentine grasslands each spring.