Coyote Crossing

One of the steadiest jokes in the plant world — for rather nerdly definitions of the word “joke” — is the degree to which a person must constantly relearn the proper Latin names of plants. Just as soon as you get used to calling something a Zauschneria, it becomes an Epilobium. When I first started paying attention to such things, older works of reference still referred to Mahonia species as Berberis; now there are some advocating that Mahonia be stripped of its rank and re-subsumed into Berberis.

The general impression seems to be that the scientists change the names because they have nothing better to do, that they spend hours in academic symposia arguing whether a cholla is an Opuntia or a Cylindropuntia or an Austrocylindropuntia, for no more reason than that their academic reputations are staked on the outcome: a counting coup on the giant shaggy beast of taxonomy. Or maybe it’s the influence of the multinational nursery plant label printing cartel, who respond to sluggish third-quarter earnings by pushing for a whole slew of renamings so that sales will rise as nurseries relabel their stock.

One renamed genus of special interest here in Southern California bears the common-names Lord’s Candle or Spanish Bayonet, names inconveniently shared with related species in other parts of the country. It’s a prominent denizen of the chaparral, or at least it’s prominent when it sends up ten-foot-tall spikes of creamy white flowers. It’s also prominent when you walk into one. There is just about no way to touch a Hesperoyucca whipplei without feeling pain. You can bring your fingertip up to a leaf’s terminal spine as asymptotically as Zeno’s tortoise approached the finish line, and in all likelihood you’ll still yelp when the fiendishly sharp point makes contact.

Calling the plant “Hesperoyucca whipplei” can prompt almost as many yelps among SoCal botanizers. The plant is still widely known as Yucca whipplei, not just in hikers’ conversation but in august references such as the Jepson Manual. Despite the unfamiliarity of the longer name, people have been using it for almost as long as the shorter alternative. It was 1871 when botanist Georg Engelmann divided the genus Yucca into two “sections,” Hesperoyucca and Euyucca, the first comprising nothing but Yucca whipplei. Assigning Hesperoyucca the rank of genus was first suggested in 1892 by Kew Gardens botanist John Gilbert Baker.

In 1902 William Trelease, in the Annual Report of the Missouri Botanical Garden, seconded Baker:

Yucca whipplei is the name proposed by Dr. Torrey, and still commonly employed, for a plant which, when in bloom, forms one of the most striking and beautiful features of the Coast-range vegetation of southern California. From all other Yuccas it differs in the slender style rising abruptly from the top of the ovary and capitately enlarged into a papillate stigma, and in possessing somewhat glutinous pollen, as well as in certain capsular characters, which led Dr. Engelmann to give it the sectional name Hesperoyucca, which both Mr. Baker and the writer have proposed to employ as a generic name.

The Yucca queen Susan McKelvey — a compelling historical figure who renounced an affluent life and marriage to botanize in the desert Southwest — disagreed with Baker and Trelease in her out-of-print, impossible-to-find-a-copy-of magnum opus Yuccas of the Southwestern United States, demoting “Hesperoyucca” to a mere division of genus Yucca.

My own true love the Joshua tree, Yucca brevifolia, was also split out of genus Yucca by Trelease in that self-same 1902 paper:

The Joshua tree of the Mohave desert region, the largest and most imposing of the Yucceae of the United States, which was first called Yucca draconis arborescens by Torrey, subsequently Y. brevifolia by Engelmann, and which is now commonly known as Y. arborescens, differs in its collective flower and fruit character about as much from typical Yuccas as does Hesperoyucca. In separating it from Yucca, I have thought best to apply to it as a generic name the sectional name Clistoyucca under which Dr. Engelmann separates it from the other species of Yucca, since there can be no question as to the applicability of that name to this particular tree, though Dr. Engelmann subsequently found it desirable to add Y. gloriosa to this section, to which the writer afterwards added Y. gigantea. Only the one species is known.

Clistoyucca arborescens is a pretty name, but it was rejected by McKelvey as well, and Clistoyucca, minus Y. gloriosa and Y. gigantea (now Y. elephantipes), was relegated to reduced status within Yucca, as “section Clistocarpa.”

Yucca draconis is an even prettier name, and the shame of its having been previously assigned to the species now known as Yucca aloifolia can scarcely be withstood. (John Torrey, in first describing the Joshua tree, had apparently guessed it to be an arborescent form of the already kinda arborescent Y. aloifolia.) But for a chance arrangement of historical events, Southern Californian rock climbers might revere Dragon Tree National Park as their local mecca. As it is, one can only gaze at historical documents and sigh wistfully, as with this 1880 photograph by Landscape Photography Patriarch Carleton Watkins:

In any event, the arguments over whether a given species, or group of species, best fit one generic pigeonhole or another may seem a bit arbitrary to the lay person. And in the past, the justifications for the rearrangements could tend toward the subjective. Taxonomists chose one characteristic or another — often floral or fruit anatomy, as those tend to vary more among related species, and Old Two-Name himself, Karolus Linnaeus, used floral morphology as the basis of his plant classification system anyway — and sorted species into genera based on sets of those characteristics. Many of the judgments were subjective. If half the plants in your sample have a floral tube three inches long, and the other half have a floral tube a millimeter long, is that difference enough to justify two genera? What if half of each group has spongy fruit, half the remainder of each group have gelatinous fruit, and one or two species in each group never sets fruit but reproduces vegetatively? The arguments could last for centuries. It’s hard enough, sometimes, to determine whether two groups of plants belong to the same species, and species at least have one possible objective standard: members can usually interbreed and produce fertile offspring. Determining a genus adds another layer of abstraction to the mix. 

A genus is a hypothesis more than anything else. Until a couple decades ago, a genus was a hypothesis that attempted to answer a rather vague set of questions: given available data about physical characteristics, are the species in the potential genus more like one another than not, are they more like each other than they are like species outside the potential genus, and is the potential genus relatively compact? I know: my eyes are glazing over too. It’s a pretty good system nonetheless, once you get away from the abstract and start talking actual traits. Take several dozen examples of each species, measure the multiple traits you have in mind, plot them all on a scatter chart, and the clumps of dots might just support your contention that species X and Y deserve to be split out into their own genus, or that genus A ought to be folded into genus L.

But two technological advancements happened in the early 1990s that changed everything. One was the advent of powerful computers cheap enough that a biology lab at a small state-funded college could afford a dozen of them. The other was the development of DNA replication by way of the polymerase chain reaction. Suddenly, it became rather straightforward to generate huge amounts of a given organism’s DNA, which could then be read — “sequenced” — with any of a number of complex technologies. The sequences of different organisms could then be compared, with the number crunching done by shiny new, massively powerful 486es and Apple Quadras.

Biologists could thus take equivalent stretches of DNA from groups of related organisms, say 500 base pairs or so at a time, compare and contrast the sequences, and figure out which groups shared which accumulated mutations.

This may seem unduly wonkish, a mere shift of the plants’ compared physical characteristics to the molecular level. But the DNA information is more than mere physical makeup: it is a map of the organism’s ancestry.

This changed everything. As evolutionary theory quickly spread through the world of the biological sciences in the late 19th and early 20th centuries, biologists had increasingly sought to make their taxonomic pigeonholes bear some relationship to actual ancestry. With DNA sequencing an everyday reality, they could do so accurately. There was a sort of internecine war for a few years between the old-line, compare the gross morphologies taxonomists (pheneticists) and new-wave DNA-sequencing taxonomists (cladists), which the cladists soon won. A lot of things get called a paradigm shift that don’t really deserve the label. This really was one.

It was a new approach to how we even think of taxonomy. The whole notion of Linnaean taxonomy was subtly undermined. It had long been accepted that the definitions of different taxonomic ranks were fuzzy, somewhat arbitrary, at best close approximations of the diversity of life. It was the closest thing we had to an accurate system, and it served us well. But with the advent of cladistics, an alternative loomed: instead of a categorizing system that described what possible relationships among organisms could well be, we could now start mapping the actual lines of descent of each living thing on Earth. Linnaean taxonomy was the bitmap, cladistics is the vector art — or maybe the better allegory would be fractal generator.

The seemingly constant renamings, then, rather than being a source of irritation and resentment of one-upmanship by show-off botanists, become a cry of joy.  We thought there was such a thing as a Zauschneria, but it turns out we were misled by surface appearances and thought they were distinct from Epilobiums, and they’re not, so we correct our earlier error. We have discovered something new about the relationships among all living things! We got it wrong before, and now maybe we have it right, and it’s not about the names so much as it is about the unique history of each species, each genus.

And the definition of a genus has been affected profoundly. It now has a discrete physical model: a genus is a clade. A clade, the notion from which cladistics derives its name, is essentially a common ancestor and all its descendants. The clade “pine trees,” for instance, contains the most recent common ancestor of all pines, and every one of its descendants that has ever lived.

That “every one of its descendants” thing is important. If you exclude any descendents, the group becomes what the cladists call “paraphyletic,” and thus not a clade. Take reptiles, for instance: the class Reptilia, one of the four canonical groups of vertebrate land animals (birds, mammals and amphibians being the other three) is paraphyletic. The most recent common ancestor of all reptiles has descendants that are generally left out of the set of “reptiles”: the birds, who are the descendants of dinosaurs. Unless you include birds in the category reptiles, “reptiles” isn’t a clade.

This becomes important in defining which genus the SoCal Bayonet belongs to. Yucca, to be a valid genus, should be a clade. That’s not a hard and fast rule, but biologists do try to follow it. If the common ancestor of Yucca whipplei and all other Yuccas has any descendants that aren’t Yuccas, then there’s a problem.

And in fact it turns out, based on data from DNA seqencing, that Yucca whipplei seems to be much more closely related to plants in the genus Hesperaloe than it is to any other Yucca. (Hesperaloe, a genus with about half a dozen species, was tentatively included in Yucca in the 19th century but Engelmann split it out in 1871, and as far as I know no one’s tried to put it back.) So either we have to move all Hesperaloes to genus Yucca, it would seem, or Yucca whipplei needs to come out. And given the Law of Priority, in which the earliest valid name takes precedence over more recent names, Hesperoyucca whipplei the SoCal Spanish Bayonet must become. (It’ll probably take another century for the name to catch on among the public.)

As for Yucca brevifolia, a.k.a. Clistoyucca arborescens, a.k.a. Yucca draconis arborescens? It turns out that once you exclude Hesperoyucca, genus Yucca with Joshua trees included is a perfectly good clade. Joshua trees will not be getting their own genus anytime soon.

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An excerpt from Walking with Zeke:

March 23, 2004
We’ve named the rabbit Thistle. Or he named himself: that was the one name he responded to at all. Smart bunny: the second-runner-up name was “Stu.”

Thistle was running around in the back yard this morning. We’re trying to acquaint him and Zeke in a controlled fashion, so that they can keep each other company without us watching every second. But it seemed, this morning, like several million years of racial memory were manifesting themselves in Zeke’s pointy little brain. The rabbit would run up the cinder block path, and every hair on Zeke’s body would stand at attention.

I trust Zeke not to inflict deliberate harm: he’s always been very gentle with small pets. But after a couple laps around the garden, nose just inches behind Thistle’s tail, I started worrying about an accidental stomp, not to mention inflicting too much stress on the rabbit. Rabbits do die of fright.

So I called Zeke, and after a minute, when the commands finally registered on his rabbit-addled mind, he came running toward me.

With Thistle in hot pursuit, nipping at his heels. I think they’ll be fine.

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The third installment of Carnival of the Arid will appear here on Wednesday, April 1. That’s a week from tomorrow! You still have plenty of time to submit your desert-themed blog posts by Tuesday the 31 of March, which you can do by leaving a comment here or by .(JavaScript must be enabled to view this email address)

The canonical description of Carnival of the Arid: Submissions should have something to do with a desert somewhere in the world. (If you’re not sure whether your work is desert-related, check out this definition at Wikipedia, and if you’re still not sure, send it in anyway.) Submissions can be scientific in nature, or history, or travelog. Images are welcome, photographic or otherwise. Discussions of culture and politics are welcome if they’re desert-related. The one restriction, other than geographical, is that — at least when I’m compiling it — paeans to destroying the desert probably won’t make it. (Developers and ORVers take note.) Paeans to preserving or protecting the desert are fine, as are alerts of current pressing issues.

And if you’re so inclined, please alert readers on your own blog or Twitter feed of this coming deadline with a link to this post. The more submissions we receive, the more fun CotA#3 will be!

(For the reference of those of you who missed the first two Cs ot A, you might want to spend a few moments cruising through some of the wonderful submissions in Carnival of the Arid number one and number two.)

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One day melds into the next. I sleep fitfully, wake late, write nothing for days on end. I stare at the screen, get up, get more coffee, fall asleep drinking coffee.

We walked into the hills three days ago, my gaze turned sullen inward. Ceanothus bloomed white by trailside and the scent of Boronia, hidden somewhere, rain not-yet-fallen and a craving at the top of my spine, and we found a place to sit.

The city spread below us. This is the prettiest city I have lived in, if I look at it in a certain light; granite peaks mantling murals, pupusas for sale next to the gay thrift store, signs advertising хлеб, the smell of poppy seeds and cologne. And I long for the creosote.

I long for the creosote, these days when the sun climbs in the sky, the espresso and boronia distracting me only a little. I burden my love by not talking about it. I carry it around in me instead.

We watched the sky for a while and then climbed again.

Wheeling overhead, two black forms: ravens. I stopped, watched them circle behind the eucalyptus. I lost them in the foliage for a moment, then one of them stepped from the brush not ten feet away from us. It sized us up. It looked us up and down. And then it jumped into the canyon, swooped, gained on a thermal and whirled above us again, and just as I was thinking to myself how pleased I was that it inadvertently chose a spot to alight where I had a good view, it landed again, closer to us this time.

We looked at each other for awhile, raven and man, and I felt something in myself release. “I think I got what I came for,” I said, and the bird followed us down into the city streets for a while.

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