Monday, November 16, 2020

Tweedy's Pussypaws' Tortuous Taxonomic Journey

Tweedy's pussypaws has long challenged plant taxonomists. Should they abandon Darwinian evolution for an alternative? Photo by Hike395.

Tweedy's pussypaws lives here! Tronsen Ridge, Wenatchee Mountains. Photo by brewbooks.

In the summer of 1883, in the Wenatchee Mountains of Washington Territory, Frank Tweedy and T.S. Brandegee went exploring, perhaps hoping to climb Mt. Stuart. En route they spotted striking plants among the rocks, with thick roots, broad fleshy basal leaves, and salmon-pink flowers an inch across. They collected one plant, and once back in camp, arranged it carefully in a plant press for drying. It would be sent to the great North American botanist, Asa Gray, at Harvard.
Specimen 37514, Gray Herbarium, Harvard. Washington Territory, 1883 ("Mt. Stewart" is Mt. Stuart).
Minor damage and loss of color due to long drying time (no other option on early expeditions). Material was removed from the fragment packet for imaging.

Frank Tweedy was a civil engineer, with a degree from Union College (New York). After graduation, he worked as a surveyor in the Adirondack Mountains, followed by a stint as sanitation engineer in Newport, Rhode Island. All the while he collected prodigiously, publishing notable finds in the Bulletin of the Torrey Botanical Club. Then in 1882, he boarded a train and headed west.

Townshend Stith Brandegee was a civil engineer with two degrees from Yale, the second in botany. By the time he collected with Tweedy in the Wenatchees, he was well-respected for his botanical knowledge of the American West, having been on four survey expeditions. Several of Brandegee's articles in the Botanical GazetteFlowers and Snow and Timber Line in the Wasatch Range—show his attentiveness to plant ecology as well as floristics.
Left: Frank Tweedy, 1875. Union College Special Collections. Right: Townshend Stith Brandegee, date unknown. Jepson Herbaria Archives, U. California, Berkeley.
In 1882, Tweedy and Brandegee were hired by Richard U. Goode of the Northern Transcontinental Survey (NTS), which was established to lay out a route for the nation's northern railway. Both men were surveyors professionally, but it was no secret that plants were their passion. In fact, they were encouraged to collect [1]. On August 5, 1893, Goode wrote in his diary, "Yesterday Mr. Tweedy collected for me over 60 kinds of flower-bearing plants within a few rods of camp. They are now being dried ...".

Frank Tweedy found himself in an exciting new botanical world. Not only was the flora unfamiliar to him, it was poorly-known in general, thereby offering fresh thrills—novelties! Unfortunately this term has largely fallen out of use; now we call them "species new to science".

We don't know what Tweedy and Brandegee thought of the plant they found near Mt. Stuart. The oldest label on their specimen (see image below) indicates they didn't realize it was a novelty. Based on the label, it appears Brandegee thought it was Claytonia megarhiza, the fell-fields claytonia—a related plant also found in talus and scree in western mountains.

But attached to the upper right corner of the sheet is a message from botanist William Marriott Canby (head of Economic Botany for the NTS) absolving Brandegee. There was a mixup in labels! Canby wrote, "Tweedy has just sent me his #s 898 and 900 Coll[ected] 1893. #898 is Calandrinia Tweedyi and 900 is Claytonia megarrhiza."

The next oldest label (bottom right corner, below Brandegee's) documents Professor Gray's decision that the plant was a novelty. He named it in Tweedy's honor, writing "Calandrinia tweedyi" on the label—but only after crossing out "brandegei"!
Brandegee label above, Gray annotation below; note edit (red arrow). "TYPE" (blue arrow) marks this specimen as the holotype, the basis for describing the new species, Calandrina tweedyi.
What was the reason for Gray's edit? Perhaps friction between Brandegee and Gray was already developing, one more example of the growing rift between field botanists and "experts" in academic institutions. "they held Gray in high esteem and generally agreed with his scientific principles, [but] the Brandegees [2] eventually claimed a superior ability to classify and appropriately name the plants they had collected ..." (Carter 2011).
Specimen V211615, U. British Columbia Herbarium. Washington, 1996. Faster drying makes better specimens. Note the different name on the label.

In school, budding botanists are taught to use standardized plant names made of Latin(ized) words—known as scientific names. Whereas common names vary from region to region, a plant has only one scientific name ... or so we're assured. But that's only true if taxonomists keep their mitts off it.

Scientific names are intended to reflect evolutionary relationships. For example, species in a given genus are thought to be closely related, evolved from a common ancestor. But sometimes it's hard to decide in which genus a species belongs, and as our understanding evolves, name changes may be needed [3]. Tweedy's pussypaws has been especially difficult in this regard.

Click on image for a "clearer" view.
Asa Gray (far left above) devoted his last decade to his life goal—the Synoptical Flora of North America, a compendium of all known species ordered by evolutionary relationships (Gray was a strong proponent of Darwinism). Several volumes were published before his death in 1888, but volume 1 part 1, which included Tweedy's pussypaws, wouldn't appear until 1895-97 (published in fascicles).

By that time, the pussypaws had been renamed twice! In 1893, Thomas Jefferson Howell, a well-respected self-taught botanist in the Pacific Northwest, moved it and several thick-rooted relatives to a new genus, Oreobroma—"a natural genus, named in allusion to the edible fleshy roots." He made the name change himself, being long frustrated with decisions by experts far away. "... the books and papers [of the experts] relating to these plants present many incongruities, according to the views of field botanists who are better acquainted with the real characteristics of the plants."

But Oreobroma tweedyi didn't last long. The next name change appeared just a few years later in Gray's Synoptical Flora, by then under the leadership of protégé Benjamin Lincoln Robinson. Robinson saw no need for a new genus, instead assigning Tweedy's pussypaws to Lewisia, where it rested for almost a century.

In the mid 1990s, Rafaël Govaerts at the Royal Botanic Gardens, Kew, moved the pussypaws from Lewisia to Lewisiopsis, another new genus. This was one of many name changes he published in the World Checklist of Seed Plants, without explanation! This drew loud criticism, understandably (see Schmid 1996).

Govaerts's decision was not accepted. In Flora of North America (FNA, 2003)—considered the definitive treatment for North American plants—Tweedy's pussypaws became Cistanthe tweedyi [4], based on work by Mark Hershkovitz. However, the FNA authors finished with a warning: based on DNA analyses, "inclusion of [Tweedy's pussypaws] appears to be somewhat equivocal and it might best be treated as a distinct genus."
Tweedy's pussypaws is popular with gardeners, and has received the Royal Horticultural Society’s Award of Garden Merit. From Curtis's Botanical Magazine, 1899 (more here).

This story ends (for now) in Santiago, Chile, where Hershkovitz, who had studied Cistanthe and its relatives for years, was dismissed from the University for lack of funding. Living on the streets with support from friends, strangers, McDonalds employees, and the Reshet Foundation, he "abandoned mathematical interventions and statistical analyses" and considered alternative evolutionary models. Tweedy's pussypaws is likely a hybrid, explaining its similarity to both Lewisia and Cistanthe. Hershkovitz called it Lewisiopsis tweedyi.

Speciation by hybridization is not some wild idea from a crazed street person. In fact, it's now (finally) widely accepted that "The origin of species is more complex than Darwin envisaged ..." For more, see How hybrids have upturned evolutionary theory in The Economist.
Tweedy's pussypaws by any name would be just as lovely! Photo by Richard Droker.

Notes

[1] In the mid to late 19th century, natural history was at its heyday in North America. Exploratory expeditions often included a botanist.

[2] Wife Katherine Brandegee also was a botanist. The couple made many important and long-lasting botanical contributions, especially in California and Baja California (see Carter's excellent article).

[3] It has been proposed that plants be given names independent of evolutionary relationships. Then they wouldn't have to be changed as our understanding changes. I have just a vague memory of this, from systematics classes 40 years ago. If you're familiar with such proposals, please leave a Comment.

[4] Currently, three names are commonly used: Lewisia tweedyi; Lewisiopsis tweedyi, e.g., in Wikipedia and among gardeners; and Cistanthe tweedyi, which seems to be the most popular one among taxonomists, at least for now.

Acknowledgements and Sources (in addition to links in post)

Once again, a huge "thanks" to Biodiversity Heritage Library for providing quick and easy access to older botanical literature. I couldn't have done this without you! Tropicos Name Search was essential for tracing the tortuous path of Tweedy's pussypaws—both its names and the characters involved. 

Carter, Nancy Carol (2011). "The Brandegees: Leading Botanists in San Diego." Journal of San Diego History. 14 (4): 191–216. PDF

Goode, R.U. 1883 (1990). Ed. C.W. Tazewell. The Goode Diary: A personal journal of the Northern Transcontinental Survey, 1883. Virginia Beach: WS Dawson Co., 1990.

Govaerts, Rafaël. 1999. (ca. 1996 originally). World Checklist of Seed Plants 3(1): 21. (Lewisiopsis tweedyi)

Gray, A. 1887. Contributions to American botany. Proc. Amer. Acad. Arts 22:270-314. (Calandrinia tweedyi)

Hershkovitz, M.A. 1990. Nomenclatural changes in Portulacaceae. Phytologia 68:267-270. (Cistanthe tweedyi)

Hershkovitz, M.A. 2019. Systematics, evolution, and phylogeography of Montiaceae (Portulacaceae). Phytoneuron 2019-27:1–77. Don't miss the Acknowledgements, p. 65 (Lewisiopsis tweedyi)

Howell, T.J. 1893. Rearrangement of American Portulacaceae. Erythea 1(2): 32. (Oreobroma tweedyi)

Lesica, P., and Kruckeberg, A. 2017. Frank Tweedy (1854-1937); in Potter, R., and Lesica, P., eds. Montana's Pioneer Botanists. Montana Native Plant Society.

Robinson, B.L. 1895-97. Lewisia; in Gray, A. Synoptical flora of North America, v. 1 pt. 1. (Lewisia tweedyi)

Schmid, R.C. 1996. Govaerts, Rafael. "World checklist of seed plants" [book review]. Taxon 45:579-580.

1 comment:

  1. Fascinating stuff. Interesting the rift between the field botanists and the academics. And in addition, the plant is beautiful!

    ReplyDelete