The varieties of perception and powerful opinions can make a tortuous history of taxonomy. Taxonomies give us names, and biological taxonomies, we hope, reflect entities, such as species and varieties, that exist in nature. How to define such entities, especially those things we would call species, has engendered a voluminous debate, which has raged ceaselessly since the Enlightenment, but I’m less concerned here with those definitions than I am with perception and opinion.
Whatever definition we use for species, varieties, and other taxonomic ranks, it is the characters of organisms that provide the data for our decision-making. There have been, however, those taxonomists who have had such intuitive power that characters seem to have been superfluous to their decision-making. All knowledge, I suppose, comes ultimately from some opinion, but taxonomy has suffered from the opinions of powerful taxonomists who have used intuition more other than characters. Perception, too, is influenced by opinion, but I want to think of it here as an issue of weighting—that is, some taxonomists may focus undue attention on one or a small set of characters to the exclusion of other variation, which effectively weights those few characters more in the process of decision-making.
I have a loan of specimens of Fendlerella (little fendlerbush), a genus in the hydrangea family, from major herbaria, and I wanted know whether the specimens were identified correctly. That sounds like a simple-enough problem, but behind that lies the issue whether the taxonomic names for species of Fendlerella correspond to discrete patterns of character variation found in the distribution of the genus in nature.
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The name Fendlerella was first used by E. L. Greene in 1881 to describe what he thought was an undescribed, new species. Here’s Greene’s description of the discovery: “Last September, while exploring the highest rocky summits of the San Francisco Mountains of South-eastern Arizona, I came upon some bushes growing in the rocky crevices, and the first sight of which called forth the exclamation: ‘A second species of Fendlera!’”
The taxonomy that Greene created with the name Fendlerella was not a new genus but a part of the existing genus Fendlera. That suffix –ella connotes something diminutive, and Greene was telling us that this new species was a second, small species of Fendlera which he called Fendlera cymosa.
By 1881, however, “one of my correspondents,” Greene wrote, had told him the new, diminutive Fendlera—the Fendlerella—had already been described by Sereno Watson as Whipplea utahensis. Whipplea was, by this time, a genus known already from a species, Whipplea modesta, that was found in shady forests of the hills and mountains along the Pacific Coast of North America, as well as Watson’s Whipplea utahensis, which was described from a collection made on the Colorado Plateau. In one of those little circles of natural history personalities, it is curious that the first specimen of Whipplea utahensis was collected by Ellen Thompson. Ellen lived in Kanab, a small town in southern Utah, but the collection was made while she was exploring canyons with her brother John Wesley Powell. Powell, a one-armed, visionary explorer, is known, of course, for his adventures on the Colorado River and description of the Grand Canyon.
Greene accepted that his Fendlera cymosa was the same kind of plant that Watson had earlier described Whipplea utahensis, but he didn’t accept that the plant from the Colorado Plateau could be in the same genus as the Pacific coastal Whipplea modesta. Taxonomically, Greene made what is called a new combination—he “combined” Whipplea utahensis with Fendlera to make the name Fendlera utahensis. In Greene’s mind Fendlera utahensis would now include the plant he had originally called Fendlera cymosa and this plant would be more closely related to the other known species of Fendlera (Fendlera rupicola), which as was also distributed in the southwestern U.S., than to Whipplea modesta.
Amos Heller was one of the early botanical gypsies of the American West. He roamed the west in the late nineteenth and early twentieth centuries. Heller had round cheeks and glasses, thin hair and a thick mustache, and he was a prolific plant collector and writer. Heller enters our story in 1898, when he wrote that Fendlera (or Whipplea) utahensis “is not a Whipplea” but “neither does it agree much better with the genus Fendlera. He listed the characteristics of Fendlera that made it much at odds with the plant that Watson’s Whipplea utahensis and Greene’s Fendlera utahensis. Heller’s solution was to leave us with a genus Fendlera that had the single species, Fendlera rupicola, with a genus Whipplea that had a single species, Whipplea modesta, and to make a new genus for the plant from the Colorado Plateau. Heller reached back to Greene’s name Fendlerella for this new genus, creating Fendlerella utahensis as the name for the plant that Watson had called Whipplea utahensis and Greene had called first Fendlera cymosa and then Fendlera utahensis.
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While the name Fendlerella utahensis established itself, the idea of Greene’s Fendlera cymosa was not lost. Wooton and Standley in 1913 described a new species as Fendlerella cymosa, curiously attributing the name to Greene. To further confuse things, Wooton and Standley based the new species on plants collected in the mountains of southeastern Arizona, especially the Huachuca Mountains, but also the San Luis and Organ Mountains of New Mexico, and Guadalupe Mountains of Texas. This constrasts with Greene’s sense of cymosa as a plant of the Colorado Plateau from the northern Arizona region (San Francisco Peaks). What Wooton and Standley didn’t tell us was how their Fendlerella cymosa was different from Fendlerella utahensis.
Not enough different was the answer of T. H. Kearney and R. H. Peebles. In 1939, they combined Fendlerella cymosa with Fendlerella utahensis to create the variety Fendlerella utahensis var. cymosa. They are effectively telling us that the plants from southeastern Arizona, southern New Mexico, and western Texas are different from the Colorado Plateau Fendlerella utahensis but not different enough to be a separate species. Kearney and Peebles explained that “leaves are normally narrower and more acute in variety cymosa than in typical F. utahensis and the two forms are widely separated geographically. . .”
Although Kearney and Peebles did not provide data to support their contention, their ideas are easy to test. The specimens I have on loan cover the geographic range of the cymosa and utahensis forms. To test the ideas that leaves of the cymosa form are narrower than those of the utahensis form, I simply measured leaf lamina lengths and widths to calculate a length to width ratio and plotted those ratios with populations segregated by the regions where Wooton and Standley as well as Kearney and Peebles recognized the entities utahensis and cymosa as differing.
The results of this simple test show that many, but not all, individuals from the southern part of the range, where the cymosa entity has been recognized by some botanists, have much narrower leaf laminas than are found among populations to the north on the Colorado Plateau and in Nevada. The results, however, show something unexpected based on the writing of Kearney and Peebles: leaves of both Colorado Plateau/Nevada region and the southern area (Mexico, Texas, New Mexico, and southern Arizona) have extensively overlapping ranges for length:width ratios. We find simply a greater range of length:width ratios, including far narrower leaves, among more southern populations than among those of the Colorado Plateau and Mohave Desert. The contention of Kearney and Peebles that the southern populations have narrower leaves than the northern is only partly, perhaps insufficiently, true—it might be better to say that both regions have continuous variation in leaf length:width ratios with considerable overlap in the range of values.
This differing range of variation between northern and southern populations may point to genetic differences or simply different environmental selection regimes. We would need to conduct further research to distinguish between those alternatives.
As for the contention of Kearny and Peebles that northern and southern populations are geographically widely separated, this also is not strictly true. The extensive collections that are now available show that populations extend continuously from the Colorado Plateau to those in the south through the mountains of western New Mexico.
What does all of this mean for the taxonomy of Fendlerella? The results show greater ambiguity than some of the earlier perceptions and opinions might have led us to expect. The greater variation in the leaves of the southern populations may have a genetic and evolutionary basis, which would be interesting to investigate. Even if this is discovered to be true, it might not be sufficient to accept that all southern populations form a species or variety different from the Fendlerella utahensis on the Colorado Plateau.
Rather than focusing on leaf variation, the next research might better investigate whether we can identify genetically unique sets of populations across the geography of Fendlerella. For example, my survey of leaf variations recovered distinctive populations in a handful of geographic enclaves. Each of these distinctive population sets may be reproductively isolated and genetically differentiated—each possibly representing different species.
I would also like to harken back to Heller’s idea that Fendlerella is something different from both Fendlera and Whipplea. Our molecular phylogenetic studies have shown that Greene was wrong to ally his Fendlerella with Fendlera rather than with Whipplea. Our studies show that Fendlerella is more closely related to Whipplea than to Fendlera. Although Fendlerella and Whipplea, as they have been distinguished now for many decades, differ in vegetative form and geography, they have nearly identical flowers. We need further research to test whether the Pacific coastal Whipplea evolved from Fendlerella, especially its populations in Mexico. If Whipplea modesta evolved from ancestral Fendlerella, then Watson may have been correct after all in naming originally populations from Utah as Whipplea utahensis.
The taxonomic problems of the Utah little fendlerbush may not be resolved, but I believe we can go beyond the limitations of opinion and the weight of perception by testing ideas with data.
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Notes
The photograph is Fendlerella utahensis.
Click on the graph to see an enlargement.
I quote E. L. Greene from "Emendation of the Genus Fendlera" in Bulletin of the Torrey Botanical Club 8: 25-26 (1881) and T. H. Kearney and R. H. Peebles from "New Species, Varieties, and Combinations" in Journal of the Washington Academy of Science 29: 474-492 (1939).
I discuss information from A. A. Heller (1898) Bulletin of the Torrey Botanical Club 25: 626-629 and Wooton and Standley (1913) Contributions to the U. S. National Herbarium 16: 109-196.
Biographical information for selected botanists was taken from John H. Thomas (1979) "Botanical Explorations in Washington, Oregon, California, and Adjacent Regions" Huntia 3(1).
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