About halfway along the road from Twentynine Palms to Cottonwood Springs in Joshua Tree National Park, there is an interpretive stop called Ocotillo Patch. It consists, predictably, of a patch of ocotillos, tall woody plants that for most of the year are simply clusters of spiky poles. The patch might seem redundant for a roadside attraction, since ocotillo typifies California’s Sonoran Desert and pervades vast areas. Yet the few big specimens at Ocotillo Patch are remarkable because they are the only ones around, as I found one morning when I walked to the nearest foothills looking for more.
The patch lies where the road descends from the Mojave’s Joshua tree zone into the Sonoran’s Pinto Basin, so I expected to see more ocotillos in that direction. But the only others I saw that day were after I drove six miles south toward Cottonwood Springs and then walked for three hours up a canyon called Porcupine Wash. Just before I turned back, as startlingly turbulent black clouds abruptly filled half the sky, I found another ocotillo patch about the same age as the first—mature plants, quite large for the species. One had fallen over recently, exposing shallow roots.
I don’t know why ocotillos are so patchy there. But the patchiness was striking, particularly since they were undergoing their annual few weeks of growth. Small triangular leaves along their stems and sprays of tubular scarlet flowers at their tops made them a nexus for hummingbirds, mockingbirds, and other life that seemed incongruous in the ambient scrub and evoked a sense of isolation echoing Mary Austin’s: “Go as far as you dare into the heart of a lonely land.” They might have been holdovers from a stranger world than that of the smoke trees and catclaw acacias that sprawled everywhere along Porcupine Wash. They seemed like vegetable dinosaurs looming fantastically among botanical burros and bighorns. A chuckwalla sunning lumpishly nearby might have been some weird Cretaceous land crocodile.
Smoke trees (Psorothamnus spinosa) and catclaw acacias are bizarre enough by nondesert standards. Smoke trees are gray tangles of thorny stems that indeed resemble puffs of smoke; catclaw acacia’s newly sprouted leaves are such an improbably garish green that they might be plastic. But both species are in the huge pea family and are so surrounded by relatives even in the loneliest desert that they evoke a sense of familiarity.
Ocotillo (Fouquieria splendens) is quite alone in the Alta California desert as far as family relations go, although it has a few congeners in Baja like the “Adam tree” that puzzled Miguel del Barco. The head of the family is Baja’s cirio, Spanish for “candle,” a word that aptly describes the plant’s shape and the spray of yellow flowers at its tip. Growing up to seventy-five feet tall, cirio (either Idria or Fouquieria columnaris depending on the authority) is so odd that a botanist nicknamed it the boojum after a mysterious creature featured in Lewis Carroll’s nonsense poem, The Hunting of the Snark. Barco considered cirio the ultimate in desert peculiarity:
Finally, there belongs to the class of pulpy plants a tree which we do not know if it exists in any other part of America or the world, nor was there any notice of it in California until the year 1751, when Father Fernando Consag, as result of a trip made to the north between the Sierra and the ocean, published its existence and properties. . . . It grows without any branches whatsoever, and it grows straight and to a great height like the palms, but it does not have (like these) a crown even on its highest reaches. It only has some thin twigs all over its trunk clear to the top . . . these are full of little leaves, each of which ends up in a thorn. At the very top of these trees grow their flowers in a bouquet, but they have no fruit at all, nor can any use be made of them, not in wood for construction, and also not even firewood.
When Consag tried to make a campfire of “that scant and extremely light wood,” the smoke had given him a headache.
Nobody knows why the ocotillo family is so lonesome, but one possibility is that it is the last of a formerly much larger group now nearly extinct. This suggests that it may be very old, and although known fossils don’t prove this, ocotillos do appear antiquated because their characteristics are so idiosyncratic. They reach tree size but it’s hard to see them as trees because they’re so skeletal, which makes it just as hard to see them as shrubs. They seem to predate current vegetable categories. There is nothing quite like them, although people often think they are spindly cactuses because their “wood” is similar. As Barco wrote, “They are made of nothing else but a pulp or mass that is supported by a framework of tubes similar to that of the cardon.” But their flowers are quite different from cactuses’, and they have no surviving relatives away from North American desert and semiarid habitats.
Not surprisingly, ocotillos are among the plants Jerzy Rzedowski cited as evidence that today’s California desert evolved in Mexico, perhaps as long ago as the dinosaur age, instead of in California a few million years ago. His critique of Daniel Axelrod’s Madro-Tertiary theory, published in 1962, might seem to have complicated the desert origin problem sufficiently. But the problem got more complicated a few years later, when G. Ledyard Stebbins published a paper that also questioned the role of plants like ocotillo in Axelrod’s theory.
As Stebbins’s recollection of his attempts to get Axelrod into the National Academy of Sciences suggests, the two were friendly, having met at Berkeley in the 1930s. Academic unorthodoxy eventually propelled both to the University of California, Davis, a Sacramento Valley agricultural school that might have seemed rustic for scientists of their stature. But both found it congenial and stayed for the rest of their careers. Stebbins moved there in the 1950s when invited to create a genetics department, and he made it a center for field-oriented evolutionary studies. Axelrod arrived in the 1960s when, according to Stebbins, the geologist with whom he was closest at UCLA “couldn’t get along with the other people in the department there, and Dan followed him up.”
Axelrod’s fossil evidence on the age of California floras impressed Stebbins: “I have discussed all these questions with him very extensively, particularly since he’s come back here to Davis but even before then. I have the greatest admiration for him.” Although discussion with Axelrod didn’t invariably lead to agreement, that did not cause acrimony in this case, perhaps partly because Stebbins was one of the century’s more modest, generous scientists.
His own estimation of his best-known achievement suggests the modesty: “So, my book that really put me on the map, Variation and Evolution in Plants, did not have any really new ideas that others hadn’t talked about, but it put a whole lot of things together in a coherent picture which caused everybody to read it excitedly.” I can attest to the generosity. Encouraging comments that he made about a book of mine incited me to present him one of the first copies, a prospect he probably found less exciting than I did. But he met me in his office at the appointed time, although I noticed pajama bottoms under his trousers. He was in his late seventies then and absentminded—he once drove across California with a dead rattlesnake left on his car during a field trip. He must have remembered my visit at the last minute and rushed over so as to not disappoint me.
Stebbins’s kindness didn’t obscure his critical faculties. In 1965, he and another UC Davis botanist, Jack Major, published an article, “Endemism and Speciation in the California Flora,” that addressed themes not unlike Rzedowski’s in relation to Axelrod’s ideas. It observed that there are two main concentrations of relict plant species in the state: “one in the Siskiyou-Trinity mountain area of northern California, and the other along the northern and western margins of the Colorado [Sonoran] desert, from the Little San Bernardino Mountains along the east slope of the San Jacinto and Santa Rosa Mountains, the Borrego Valley area, and southward into Lower California.” The northern relicts include trees like weeping spruce and Sadler’s oak; the southern relicts include shrubs like turpentine broom, creosote bush, and ocotillo.
Stebbins and Major agreed with Axelrod that the Siskiyou-Trinity tree species are relicts of the Arcto-Tertiary flora, the forest that once covered most of North America and Eurasia with a greater plant diversity than today’s. But they disagreed with his idea that the Sonoran Desert relict shrubs evolved from a Madro-Tertiary flora of oak woodland, savanna, and thorn scrub in the last few million years. They thought them too numerous and desert adapted to be such recent scions of woodland vegetation, even an arid-adapted one. The shrubs seemed more likely to be relicts of ancient, widespread desert floras:
In the first place, several of the relict species . . . have their closest relatives in the arid regions of southwestern Eurasia and northern Africa, while others, although possessing relatives elsewhere in the southwest, belong to groups which are represented also in the arid and semi-arid regions of the Old World. Because of the close relationship between the Old and New World representatives of these groups, and the fact that the entire genus, or in some cases the family to which they belong, is adapted to semiarid or arid conditions, the possibility that these elements became adapted independently in the two hemispheres to arid conditions, and that their common ancestor belonged to a mesic flora, is very remote. . . .
Secondly, some of the most common species of the area are relict types related to species of the arid areas of temperate South America. . . . In all of these examples, the great similarity of the North American species to those of South America and in some instances also Africa suggests that they have evolved very little since these vicarious elements became separated from each other, and that they existed essentially in their present form when the Madro-Tertiary flora developed in the middle of the Tertiary Period. Furthermore, they are adapted to arid or semiarid conditions wherever they occur, and they have no recognizable connections with any genera of the humid tropics. Consequently, these groups probably also migrated from one continent to another as members of an ancient xeric or semi-xeric floristic element, which preceded the development of the Madro-Tertiary Geoflora.
Stebbins and Major thought it “highly unlikely” that closely related desert plants occurring on two or more continents could have reached such a wide distribution within the time when Axelrod said the Madro-Tertiary Geoflora evolved. They pointed out that most such plants remain confined to warm climates today. If the plants had migrated between the Old and New Worlds, they would have had to do so across areas such as the Bering Strait, which were too cold for them during at least the past thirty million years:
Another group of genera which are hard to reconcile with the hypothesis that the Madro-Tertiary Geoflora is derived from the humid neotropical flora includes Lyonothamnus [ironwood], Crossosoma [one of the genera I mentioned earlier that has an entire family to itself], Simmondsia [jojoba], and the two genera of the Fouquieriaceae [ocotillo and cirio]. The relationships of these genera are so obscure that they are best explained as remnants of distinctive groups which flourished before the modern families had reached their present state of development. They, also, probably existed in their present form when the Madro-Tertiary flora arose. Their connections with families of the humid neotropical flora are tenuous at best.
In effect, Stebbins and Major suggested that plants like ocotillo don’t just seem like vegetable dinosaurs, they are vegetable dinosaurs. They maintained that the presence of so many such relicts in California desert was “best explained by assuming that their ancestors were for a long time confined to a restricted, homogeneous area, and isolated from their nearest relatives by long stretches of territory unfavorable to them.” This led them to a different hypothesis than Axelrod’s:
During the early part of the Tertiary Period and the latter half of the Cretaceous Period when the dominant floras of the middle latitudes in the northern hemisphere were mesic and tropical, subtropical, or warm temperate in character, the existence is postulated of several small pockets of xerophytic or semi-xerophytic floras, similar to the caatingas [areas of scrub or dry forest growing on poor soils] of modern Brazil, and some of the valleys of the Colombian Andes. . . . Such isolated patches of xerophytic species existed not only in southwestern North America, as postulated by Axelrod (1958: fig. 2). They probably extended also from central North America to Alaska, and across Eurasia to the shores of the Tethys Sea, which occupied the present Mediterranean region. . . .
The Madro-Tertiary flora is postulated as having derived through an amalgamation of these isolated elements through spreading from these isolated areas, as aridity increased and conditions for them became more favorable. Some genera had already lost so much of their stored genetic variability that they were unable to react to these more favorable conditions by evolving new species and genera. These became the relict groups. . . . Others were able to resume active speciation, and became the large complex of the Madro-Tertiary flora.
Combined with Rzedowski’s challenge, Stebbins and Major’s article might seem a crushing rejoinder to ideas that Axelrod had been elaborating for two decades. Like Rzedowski, they brought up an entire group of plants that his confident fossil analyses had ignored. Of course, Axelrod had to ignore them because he found no fossils of them. But it is harder to see how plants like creosote bush and ocotillo could have come from the Madro-Tertiary woodland-savanna vegetation that Axelrod postulated than mesquite and acacia. For all their adaptations to drought, acacia and mesquite are “normal” looking shrubs or small trees that can compete in woodland shade, not bunches of spiky poles.
Still, Stebbins and Major didn’t reject Axelrod’s work. They didn’t challenge his fossil analyses or his idea that the Madro-Tertiary Geoflora evolved in southwestern North America. They merely suggested some adjustments of its geographical and geological elements, as they diplomatically observed at the end:
The hypothesis just presented differs little from that proposed by Axelrod (1958). He did not, however, consider evidence suggesting early migrations of semi-xerophytic warm temperate or subtropical types from the Old World to the new and vice versa. That such migrations took place seems rather likely. Once that assumption is made, then many elements of the Madro-Tertiary flora which are congeneric with elements in the Old World steppe and Mediterranean scrub floras . . . are best explained as having migrated to North America from Eurasia, or vice versa, by means of the ‘stepping stones’ provided by these small pockets of semi-arid conditions. In view of this possibility, it seems more appropriate to postulate that the Madro-Tertiary Geoflora had a diverse origin, rather than a principal derivation from a humid New World tropics.
In any case, challenges to his ideas did not discourage Axelrod. On the contrary, they stimulated him, judging from the volume of work he would produce in the next four decades. Few scientists have published in quite such bewildering abundance. The pre-1960s publications seem almost meager compared to the later ones.