Tiburon mariposa lily (Calochortus tiburonensis)

While looking for an answer to my own question, I discovered, to my surprise, that rarity in the animal and plant world is quite common. Conservation scientist Eric Dinerstein estimates that 75% of the species on earth are rare.  The US Forest Service guesses that a third of the native plants in the U.S. can be considered rare. And we have no idea how many species science hasn’t yet named; those remaining are most likely rare, since large populations would have been identified by now.  Some of these yet-to-be classified plants may be right at our feet: the tiny population of the Tiburon mariposa lily, in bustling suburban San Francisco, and a plant I consider to be pretty showy, was only ‘found’ and named in 1971.

Tiburon mariposa lily (Calochortus tiburonensis)

There are reasons. The main one is that it only grows on one serpentine outcrop on Ring Mountain, in Tiburon, California, and nowhere else on earth. I’ve written about serpentine and celebrated Ring Mountain; its mariposa lily is another thing that makes it special. One of the first Spanish land grants in this area, Ring Mountain and its environs were grazing land from 1834 until the 1960’s, when the remaining ranch land began to be sold to developers. I’m sure that the Coast Miwok tribe members, who were displaced by these land grants, knew and had a name for the Tiburon mariposa lily, which was both food and medicine for them. And I can imagine that the few cowboys who came to the top of the ridge to find stray cows would notice the flower but feel no need to find a name for it.

Oakland star tulip (Calochortus umbellatus)

As showy as the flower is up close, its modest height, single leaves close to the stem, and mottled flowers do blend in with its grassy, rocky surroundings. It can take some focusing to find them, even when they’re right in front of you. So it wasn’t until the land was being explored for preservation that the flower was ‘found,’ classified as a calochortus, and given its official scientific name: Calochortus tiburonensis. The species name comes from the Greek words ‘kalos’ and ‘chortus’: beautiful grass. Mariposa is the Spanish word for butterfly. There are lots of mariposa lilies in the west, over 70 species, 28 of them endemic to California. Two others grow on and around Ring Mountain: the also rare Oakland star tulip and the yellow mariposa lily.

Yellow mariposa lily (Calochortus luteus)

And there’s still more rarity: tiny, delicate Marin dwarf flax grows among the mariposa lilies on the serpentine, and Tiburon paintbrush grows on the next hill to the west. One subspecies of the otherwise not-rare jewel flower, the black Tiburon jewel flower, grows in a neighboring preserve, along with the rare Tiburon buckwheat. As long as a plant population can keep itself healthy and reproducing, rarity itself is not a threat. But, with the exception of the yellow mariposa lily, all the plants named here are considered endangered, defined as ‘a species in danger of extinction within the foreseeable future throughout all or a significant portion of its range.’  If your range is a few hundred square yards of rock, it’s easy to be threatened with extinction.

Marin dwarf flax (Hesperolinon congestum)

Why all this endangered rarity in one small area? In this case, serpentine is the first limiting factor. Any plant growing on it has to be adapted to its toxic qualities, but those skills enable survival, not abundance. So you start with a small population. Then, in the case of wealthy Tiburon, you build roads, houses, driveways, stores, tennis courts. Gardens and lawns are planted in dirt carted in to circumvent the toxicity in the soil. Even in the preserved areas, fire roads have to be built and maintained to protect the nearby houses, which disturbs the soil and opens it to a flood of opportunistic invaders, usually annual seeds that sprout quickly on small root systems, taking water, nutrients, and light from the slower natives. According to the U.S. Forest Service, nearly 20% of the plants on the endangered list got there because of invasive non-natives, and half of at-risk plants have been affected by them.

Black jewel flower (Streptanthus glandulosus, subspecies niger)

The more an environment changes from its original ecology, the fewer plants native to that place will be able to grow. And it’s not just the actual ground the plant is growing on. Pollinators like bees, birds, bats, beetles and butterflies need space for their own environment, which isn’t necessarily the same as the plants they pollinate. They may have come from a neighboring field, or upland woods, now houses or a shopping center. Animals and birds leave areas that are too cut up, which don’t allow them the contiguous space they need to feel safe when building nests and foraging for food. So the ancient, intricate relationships of animal—plant—place are severed.

While human activity does the bulk of this severing, natural forces have a role. Floods, fires, droughts, landslides, and insects can all come in forms devastating to small plant populations, rendering them unable to reestablish. And intrinsic qualities make a difference. The Tiburon mariposa lily’s seeds are too heavy to be wind borne, so they fall at the feet of the existing plants, replenishing the colony, but not increasing its area.

Tiburon buckwheat (Eriogonum caninum)

Despite all the threats, rare plants continue to bloom in Marin, which is in one of the few ‘rarity hotspots’ in the U.S. Because each individual plant’s numbers are low, there’s room for a variety of species, and the tasks of that ecological niche can be shared among them, along with their interdependent creatures, like bees, butterflies and beetles. One of the great glories of our planet is the wild abandon with which it has come up with species of animals, insects and plants. And we only know of 1.7 million of them! Of those, only a tiny percentage has been studied; we have no way of knowing how many more there are.

Given that abundance, the fact that 20,000 species are on the verge of extinction may not seem disastrous. But, if that rate continues, we could lose 75% of the earth’s species in the next few hundred years, a mass extinction on par with the disappearance of the dinosaurs.  Many ecologists refer to our current rate of species loss as the sixth great extinction, and fear it will only accelerate as the climate continues to change.

Tiburon paintbrush (Castilleja affinis, subspecies negecta)

Conservation scientists and organizations the world over are working on this challenge. There’s no one answer. All of the possible mitigators have a place: habitat preservation and restoration, nature-centered design, sustainable agriculture, renewable energy, cradle-to-grave manufacturing practices, scientific literacy, etc. We need both a lot of grand schemes, and millions of small gestures that we can make in our own kitchens and gardens, in our neighborhood, in our local parks.

On my last visit to Ring Mountain I went early in the morning, to beat both the heat and the wind. As I was leaving, I met two of the county naturalists, setting up a table of snacks and literature. It was a volunteer day, and people were arriving to pull out one particular invasive thistle, which was new to the preserve, and very aggressive. When we look at the scale of the challenges we face, it’s hard to have faith that small actions will help. But, as I found out later, 7 people showed up and pulled 1500 invaders, a huge difference in a small preserve. Grand schemes are enacted exactly this way, stem by stem, person by person, each one of us carrying one of the delicate threads in the whole.

Tiburon mariposa lily (Calochortus tiburonensis)

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