The Prince of Plant Collectors and the Largest Cactus in the World

By Audrey Clark

When the Prescott College coastal ecology class for which I was a teaching assistant left the field station on the shores of Kino Bay in early January, the sun shone and the sea was calm.  We loaded the students into a couple fiberglass fishing boats and sped off toward the Midriff Islands.

Kino Bay is about a third of the way down the Gulf of California, in what is known as the Midriff Island region.  There, the coasts of Baja and mainland Mexico pinch in slightly and islands are scattered across the waist of the Gulf.  The Midriff Islands cause cold, nutrient-rich waters to well up from the trenches to the south, which feed an abundance and diversity of life.  Many bird species breed almost exclusively on islands in the Gulf of California, often just on one or two.  The Sonoran Desert blankets the land around the Gulf, so that the largest cactus in the world, the cardon (Pachycereus pringlei), towers next to the dunes and waves.

Cardon cacti are the icons of the Mexican Sonoran Desert.  They form forests, have a trunk that can be over seven feet in circumference, grow up to 50 feet tall, and can have upwards of 80 branches.  You can even climb them like trees because the aged, leathery, lower trunks lose their spines.  Cardon look very much like saguaros, those quintessential cacti popularized by Western films and Mexican restaurants.  The main difference between the two species is that a rather large saguaro might have 10 arms, whereas a cardon can easily have 80.

When we circled the cactus-covered island called Cholludo, we looked up into the backlit cardon cacti to see thirty turkey vultures sunning themselves, their silvery primary feathers glowing against their black silhouettes.  Later, we sped out to Isla San Pedro Martir, the most isolated island in the gulf, on a glassy sea.  San Pedro Martir appears perpetually covered in snow—but the “snow” is actually bird guano and the reek is, at times, choking.  The professor told us that the Yaqui Indians were once enslaved on small islands in the Gulf, forced to harvest the guano for its phosphorus, which was then used by the Mexican military to make explosives.  I thought of the sun, and the lack of fresh water, and the stench.  Now, the island hosts the northernmost breeding colony of red-billed tropicbirds and a substantial blue-footed and brown booby colony.

We sat on the gently rocking boat in a nook near shore, surrounded in the water by curious cavorting sea lions.  We took in with all of our senses the white, cardon-covered black volcanic rocks while hundreds of boobies wheeled above the island’s peaks and tropicbirds circled us like angels.  San Pedro Martir hosts only a few plant species, due to its caustic burden of bird feces.  The cardons survive somehow, even though they are coated with the stuff like paint-splattered furniture.  On our way home, a humpback opened its maw not ten feet from our boat, so that we looked down into its mouth of baleen.

A year later, I came to the University of Vermont for graduate school and was awarded a research assistantship at the university’s Pringle Herbarium.  An herbarium is like a library, but full of pressed plants instead of books.  Botanists use herbarium specimens to understand the differences between species, their ranges, population trends, and more.  Darwin used the specimens he collected on his voyage to develop the theory of evolution by natural selection.

My job at the herbarium was to dig through archives, read books, and interview former employees and then write up a comprehensive history of the herbarium.  In my diggings, I came across an article that mentioned cardon cacti.  The February 6, 1889 edition of Garden and Forest, a horticultural journal, read:

One of the most interesting of Mr. Pringle’s numerous Mexican discoveries is the great Cactus [sic] which now bears his name, and which he found during the summer of 1884 growing among the hills and mesas south of the Altar River in north-western Sonora.

The stems of this remarkable plant, which divide irregularly above the base into numerous large branches, do not attain the great height of its near relative, the now well known Suwarrow [sic], the Cereus giganteus of Arizona and Sonora.  They are sometimes, however, more than thirty feet high and thicker and more ponderous than those of any Cactus known….

Nothing more was seen of this plant until October, 1887, when Dr. Edward Palmer, the well-known explorer of Mexican botany, visited San Pedro Martin [sic] Island, in the Gulf of California, which he found covered with a forest of these trees…one of the strangest and most remarkable forests which has yet been seen in any portion of the North American Continent.

It appears from Dr. Palmer’s notes that San Pedro Martin Island…is partly covered in a deep deposit of guano, which Mexicans and Yacqua Indians are now engaged in collecting for export.  The Cereus is called Cordon by the Indians, who gather the fruit in great quantities.

The Latin name of cardon, Pachycereus pringlei, means “Pringle’s thick columnar cactus.”  Cyrus Pringle, one of the most famous and prolific plant collectors of all time, was the first botanist to collect a specimen of the cactus.

Pringle lived in Charlotte, Vermont for most of his life (1838-1911).  For the last nine years of it, he lived on the University of Vermont campus, next door to his herbarium.  Nearly every year for the last 30 years of his life, he spent several months collecting plants in Mexico.  His specimens are still admired for their completeness and careful arrangement.

Pringle collected the cardon cactus in 1884, on one of his first visits to Mexico.  When I learned that Pringle collected this cactus, I wanted to know two things: how did he collect a specimen of such an enormous cactus without mutilating either himself or his plant press?  And what did he think of his grand “discovery”?

To answer the first question, I went to the Pringle Herbarium.  On the third floor of the 200 year-old building I wandered among creaking wooden cabinets until I found the section containing specimens of Cactaceae, the cactus family.  I poked through folders of spiny specimens until I found the one containing the genus Pachycereus.  It contained one specimen, that of pecten-arboriginum.  Not P. pringlei.  I was shocked.  How could the herbarium that Cyrus Pringle founded not contain a specimen of his most striking collection?  Could it be that botanists just don’t care about charismatic megaflora as much as I do?

Then I remembered that the plant used to go under the name Cereus pringlei.  I shuffled through the Cereus folders until I found “p.”  With mounting dismay I sorted through the “p” specimens, not finding pringlei.  But then—there it was.  Just one specimen of one of the most dramatic plants on earth, in an herbarium containing over 350,000 specimens.  It consisted of a couple strips of cactus flesh and a few fruit sewn to a 12 by 18 inch piece of whitish cardboard, with a yellowed label in the lower right corner.  The label was one of Pringle’s, written in pen and ink in his barely legible hand.  The cardboard was coated in coal dust, a vestige of former herbarium heating systems.

The answer to my question of how Pringle collected the giant cactus was that rather than uprooting an entire individual, as is common when collecting other, smaller plants, Pringle simply cut a few pieces off of it and grabbed a handful of fruit—carefully.  These he squashed in his plant press (having pushed the spines sideways), dried, and then sewed onto the piece of cardboard.

What did Pringle think of his enormous cactus?  At the very least, he wanted it named after himself.  When Asa Gray, a famous Harvard botanist, immortalized Pringle in early 1884 by naming a shrub after him, Pringle wrote, “Well, I am glad not to be commenorated [sic] by some insignificant little weed under the diminutive name of Pringella.  Dr. Gray asked me if I preferred to wait to find some more showy plant; but I thought this as appropriate as anything could be….”  This was probably the first plant to be named after Pringle.  A short time later, Pringle got his showy plant, for in late 1884 he wrote to a friend about cardon: “Please throw out [the name] Cereus ponderosus; [the botanist Sereno] Watson indulged me, and gave the plant my name; it is as large as C. giganteus and only some 70 miles south of the Boundary.”

It didn’t take long for more botanists to name plants after Pringle.  He quickly gained fame for his superb and abundant specimens.  By the end of his career, Pringle had at least 4 genera, 75 species, and nearly 30 varieties and subspecies named after him.

I think Pringle loved cardon because he loved plants and desert Mexico.  He loved plants so much that he collected over 500,000 specimens in his lifetime (“I find complete happiness in this botanical work,” he wrote).  He certainly loved the desert at least as much as I do.  Though friends urged him to make his way toward lusher environs, where plants would be more abundant, he refused, saying that there was still much to discover in the desert.  In spite of the difficulty of traveling by train, wagon, mule, and on foot across Mexico’s arid landscape, into cañons and onto mesas that are still wildly difficult to access, he spent most of 26 years doing so.  In 1884 he wrote, “I spent nearly a month—March 17^th to April 12^th, on a trip through Sonora to the Gulf. [sic] of Cal.  It is a fearful country to travel, water scarce and forage for horses scarcer still.  It was like a race for life with us.”  He did it, I am sure, for the thrill of discovery and love of plants.

I love cardon for different reasons than Pringle.  I love cardon not just because they are dramatic—though I do love them for that reason.  I love them because they give the coastal Sonoran Desert a character and dimension unlike anywhere else on Earth.  I love them because vultures perch on them and boobies and tropicbirds circle them.  I love them because they are the biggest and strangest trees in the desert.