Reconciling the perception of this misunderstood habitat from barren wasteland to botanical boon
by Elise Hinman
This post is the fifth in a year-long series celebrating the 40th anniversary of the Endangered Species Act. Read the previous post here.
One can often find beauty in the most unassuming places; sometimes even the mundane is worth a closer look.
Taking these words to heart on the watershed will likely lead you to some of the rarest and most fascinating plants around Mt. Tamalpais, like the Marin dwarf flax (Hesperolinon congestum). Its petite rose-colored flowers display unique deep purple anthers and emerge from dainty, slender stems between May and July. This wildflower is a threatened plant species endemic to serpentine soils in Marin, San Francisco and San Mateo counties. What does all of this mean? Allow me to explain.
Federal and state agencies list the Marin dwarf flax as “threatened” because it is likely to be at the brink of extinction in the future. Why? Because it occurs in one (and only one!) tiny and under-appreciated California habitat often destroyed for suburban development: serpentine outcrops. Since the Marin dwarf flax lives in this one specific habitat and is confined to the Bay Area region, it is termed a “California serpentine endemic.”
Why does the Marin dwarf flax need serpentine soil to survive? It’s complicated. Serpentine has a very unique geology that gives it a peculiar nutrient profile, which reveals a special niche occupied by only a handful of adapted plants. Serpentine forms at the bottom of the seafloor, where molten rock from the Earth’s mantle rises to the crust’s surface as tectonic plates move away from one another. Over millions of years, this rock originating from the seafloor has fragmented and been exposed throughout California. Be on the lookout for it along Ridgecrest Boulevard on Mt. Tamalpais; serpentine outcrops are a greenish blue in color, devoid of most plant life, and upon a brief glance, may garner the descriptors “unsightly” or “strange.” In my mind, however, they have a Martian mystique about them.
Serpentine is low in calcium, nitrogen, phosphorus and potassium: macronutrients essential for plant growth. It is also high in magnesium, nickel and other harmful heavy metals. For these reasons, serpentine presents a harsh environment in which to grow and proliferate, and successful plant species must possess adaptive traits for survival. For example, many serpentine endemics possess high tolerances for heavy metals. Still, many serpentine species are often characterized as “dwarf” plants because the nutrient-poor environment inhibits their growth. But the soil environment presents both challenges and rewards. Since few plants colonize serpentine soils, competition for resources generally remains low between serpentine endemics.
The Marin dwarf flax has special adaptations to flourish in serpentine soils and shares its habitat with few competitors for necessary resources. Unfortunately, beyond serpentine it is a different story. In non-serpentine soils, plants do not need the same specialized adaptations to acquire resources; when nitrogen and phosphorus abound, success depends upon efficiency. Serpentine adaptations become hindrances in non-serpentine environments, making serpentine-endemic plants poor competitors. In this way, the Marin dwarf flax is “stuck”—without serpentine, it will go extinct.
If you happen upon a serpentine outcrop on your next hike, take some time to study its inhabitants. As always, be respectful of native wildlife and plant life and do not set foot in their home; serpentine plants are extremely fragile and may be the last of their kind. Instead, peer inside these peculiar islands of habitat from the edge. Take a moment to appreciate the magnificence these unique, humble and well-adapted plants have to offer.
“Everything has beauty, but not everyone sees it”—Confucius