Last June I hunted for an endangered species.

Photo by Mary Aline Stevens

Calochortus tiburonensis, the Tiburon Mariposa, is a bulb that grows wild in only one place on Earth - a single hillside in Tiburon, California, just north of San Francisco. It is federally listed as a rare and endangered species, and is almost impossible to obtain from other enthusiasts. Unlike a number of other endangered bulbs, such as Moraea Aristata, C. tiburonensis is notoriously difficult to grow in captivity. If you want to see it, you have to go look for it.

It's awkward to write about a rare species like this one, because the more people know about it, the more danger there is that someone irresponsible will go pick the flowers or dig up the bulbs. (For the record, don't do it. Wild-collected bulbs of Calochorti rarely survive in captivity; they just can't adapt to the change.)

On the other hand, anonymity can also be dangerous. A butterfly in southern California called the Palos Verdes Blue was well protected by its almost complete anonymity, until someone who didn't know better mowed the grassy area where it lived. Fortunately, it was rediscovered a few years later somewhere else.

So I'll tell my story, and hopefully help to keep the lawn mowers away. But I'll leave out some of the details on location.

C. tiburonensis has a strange history. Even though Tiburon is a heavily populated area, and has been for many years, the flower was only discovered in the 1970s. Its discovery is credited to a Dr. Robert West, who along with three other local residents brought it to the attention of science. Tiburon is a densely populated suburb of San Francisco, and it's amazing that the flowers not only survived but escaped notice for so long. The area had been thoroughly explored botanically several times.

I had read about C. tiburonensis for several years, and wanted to see it for myself. A business trip to the area in June, the height of the Calochortus season, gave me an opportunity. The heavy rains of 1994-5 had produced a bumper crop of bulb flowers, so this was the best time to look. The only trouble was that I didn't know where exactly to start. Tiburon is a peninsula, and it has a lot of hillsides. Because C. tiburonensis is so rare, the printed sources I checked were deliberately vague about where to find it. In fact, I had been told by someone knowledgeable that it was closly guarded. I pictured a razor-wire fence, guards armed with walkie-talkies, and maybe some trained attack dogs. I wasn't sure if I would be able to get near it, even if I did find the site.

All I had to go on was some vague hints. Combining them with a detailed map of the area, I made an educated guess to look along a particular road. The only problem was, the road I had found on the map didn't exist in real life. Instead there was a residential area that dead-ended into a hillside.

I was confused, but decided to take a look at the hillside anyway. There was a very old barbed wire fence, almost completely collapsed, and the vague outlines of a foot trail leading uphill along the fence. The ground was right - a thin layer of red-brown oxidized soil over solid serpentine. There were none of the European annual grasses that have taken over most of California, just native bunch grasses and a huge number of small Brodiaeas. Looking around, I couldn't see any Mariposas sticking up above the grass, which is the way you usually spot a stand of them.

Fortunately, I have learned to watch where I step, and so I didn't walk on the first Tiburon Mariposa I encountered. It was lying across the path, a small plant with a short stem and a flower about an inch and a half across.

It's hard to describe the flower of C. tiburonensis. Picture a flesh-colored radar dish covered in blond fur and you'll have a rough idea. There are three diamond-shaped petals, slightly cupped, straw-colored, and densely covered in curly hairs. The petals are stippled and lined in shades of brownish maroon. In the center of the flower is a thick style, with six canoe-shaped anthers sticking out of it at a 90 degree angle, parallel to the petals.

Most Calochortus flowers are indisputably beautiful. This one is indisputably odd. It has the same feeling of extra-terrestrial strangeness that you get from some Fritillarias.

Once I spotted the flower, it was easier to understand why they went undiscovered for so long. Because of their color, they blend in beautifully with the dry grass. But now that I knew what to look for, and I realized that they were actually low-growing (unlike a drawing I had seen), it was easy to pick out more. They dotted the hillside all around me. In some places, I had to step carefully to avoid crushing them. But they didn't extend for far - fifty yards away, they started to peter out, and I didn't spot any more. It's possible that there are other stands of them in the vicinity, but there can't be many.

I had carried a box lunch with me. I sat on an uncomfortable rock and ate lunch with the Mariposas.

They have a great view. Their hillside, about fifty feet away from a housing tract, faces San Francisco Bay and the hills beyond. It's literally a million-dollar view, and we're lucky that the whole hillside wasn't converted to houses years ago. I was surprised that there was no physical protection for the plants - no sign, no fence, and definitely no guard dogs. I had the spot to myself, and could have picked a bouquet of endangered species if I had wanted to.

Fortunately for C. tiburonensis, it's what most people would call ugly, and so probably no one will ever bother to do that.

This flower raises a lot of qustions. How did it get there? Why Tiburon, and nowhere else? Why is it so hard to grow? What did it evolve from - it looks vastly different from almost every other member of the genus. The petal shape is something like an exploded version of a fairy lantern (such as C. amabilis), but those grow in shade, among trees and bushes. This flower is out in the open, on a sunny and windswept hillside.

Why are they so pale-colored? The Calochorti are well known for their conspicuous colors. I wish I had thought to smell these - they look a little like some Tigridia species that smell dreadful and use flies for pollination.

The only scientific literature I could find on C. tiburonensis echoed my confusion. Albert Hill concluded that C. tiburonensis is difficult to fit in the current classifications used for the genus. Its leaf and flower shape seems to fit with the section Cyclobothra, but those species are generally found in southern California and Mexico. Judging by the shape of the gland (a diagnostic feature used heavily in classifying Calochorti), the plant might be closer to section Calochortus. But those generally grow further north. He speculated that it could be an ancient hybrid, but other tests discounted that.

I don't pretend to be qualified to judge these scientific questions. My point is that if there's a mystery plant like this in the middle of a housing tract in urban California, you have to wonder what still lurks out there in the less populated parts of the state.

The Tiburon Mariposa winks at us and dares us to go out and look.