History of Agave Utahensis

Genetic research published in the Proceedings of the National Academy of Sciences of the United States of America in 2006 estimated that Agave is a relatively “young genus, between 7.8 and 10.1 million years old.” Another 2006 study from Aliso: A Journal of Systematic and Floristic Botany suggested that “the desertification of North America, which started ca. 15 [million years ago] was critical in the radiation of agaves.”

Both studies identified Mexico, particularly the Sierra Madre Occidental and the Chihuahuan Desert regions, as the geographic center of origin for Agaves, which then spread into Central and Northern South America, as well as the into southwestern United States and the Caribbean.

The desertification that helped spread agave to its present-day range took place during a period of global warming called the Miocene Epoch. During this time the Sierra Nevada, Cascade, and Andes Mountain ranges formed, each creating arid rain shadows. As moisture-rich air is driven up the mountain slopes on one side of these ranges, cooler temperatures at high elevations force the moisture to condense and precipitate, leaving the opposite side of the range dry.

The Miocene period was followed by the last ice age, called the Pleistocene Epoch, which began around 2.5 million years ago and ended 11,700 years ago. It is during the end of this period that most archeologists believe that humans began to migrate into North and South America.

Human-Agave Symbiosis

In the 1950s, Archaeologist Richard MacNeish discovered evidence of human use of agave in the Tehuacán Valley in eastern central Mexico dating back at least 10,000 years ago. A 2011 study Cordage, Textiles, and the Late Pleistocene Peopling of the Andes carbon dated rope made from agave fibers found in Guitarrero Cave in the Andes mountains in northern Peru to approximately 12,000 years ago. Both regions were home to some of the earliest examples of the cultivation and domestication of crop plants such as maize, beans, and peppers known in the Americas.

Groups such as the Maya in Mesoamerica and the Hohokam in what is now Arizona created domesticated species of agave, likely around 600ce. The Mayan domesticate agave fourcroydes (common name henequen) was grown for its fibers, used in rope making, while the Hohokham created cultivars like agave murpheyi as food sources.

The Spring Mountains

In his 2020 article in the Cactus and Succulent Journal, researcher Matthew Maggio called Southern Nevada’s spring mountains the “heartland” of agave utahensis. But what is it about this range that makes it the perfect habitat for my favorite plant?

Before the breakup of earth’s most recent super continent Pangea 250 million years ago, Southern Nevada was covered by an ancient sea, debris from which compressed over hundreds of millions of years to form the limestone that makes up most of the Spring Mountains—an important fact for limestone-loving utahensis. As Pangea disintegrated, tectonic movement pushed that fossil rich rock thousands of feet into the air, forming the Spring Mountains we see today to the west of the Las Vegas valley.

During the Miocene desertification between 15 and 10 million years ago, the Sierra Nevada, west of present-day Nevada, was one of the mountain ranges that rose up and caused the formation of a rain shadow, turning Southern Nevada into the arid habitat we know it as today.

Around 7 million years later, during the Pleistocene ice age, Southern Nevada was considerably cooler than it is today. But 11,700 years ago, the Pleistocene ended and the earther warmed considerably through a period known as the Younger Dryas.

Plant species like agave utahensis that could have survived at lower elevations during the Pleistocene became isolated in the higher elevations of the mountain ranges like the Spring Mountains during this warming. Today, the Spring Mountains are a sky island. They’re thousands of feet above the valley floor, and much cooler and wetter than the extremely dry rain shadow Mojave Desert that surrounds them. Populations that once extended through the valleys are restricted to this, and other similar sky islands.

Enter Utahensis

A large clump of agave utahensis subspecies utahensis.

There are four categories of utahensis currently recognized by botanists: subspecies kaibabensis, subspecies utahensis, variety eborispina, and variety nevadensis. In his seminal text Agaves of Continental North America, botanist Howard Scott Gentry mentions that the flowers of a. utahensis occur in three different forms: “spicate, racemose, or paniculate.” Though he didn’t mention it in his book, kaibabensis is the one exception to this rule as it is known to only produce paniculate flowers.

Spicate flowers are unbranched. Spicate agave have their flowers growing directly off their main stalk. Racemose agave has branches extending off the main stalk that each hold a single flower. Paniculate agave feature branches extending off the main stalk, which then subsequently split into multiple branches themselves, each of those sub-branches holding a single flower.

Experts typically agree that this variability suggests that the three utahensis groups other than kaibabensis—utahensis, nevadensis, and eborispina--are the result of a relatively recent hybrid of two or more other agave species, rather than the product of another type of speciation, such as geographic isolation. A similar hybrid, agave arizonica, was shown in that 2006 Aliso paper to have evolved around 200,000 to 100,000 years ago.

Some experts assert that kaibabensis is the ancestral parent species of the uthaensis complex because it only grows a single type of flower, and thus is likely not the result of recent hybridization.

Carbon dating studies of rodent droppings show that agave utahensis (possibly kaibabensis or utahensis) was present around the Grand Canyon at least as far back as 20,000 years ago, during the Pleistocene ice age, when it had a much larger and lower range.

It is difficult, and perhaps impossible, to know for certain which species contributed to utahensis’s gene pool. The experts who believe kaibabensis is the older parent contend it was that subspecies which mixed with other older species, like a. parryi or a. mckelveyana, both of which probably shared habitats with utahensis in northwestern Arizona during the Pleistocene.

It is also difficult to determine exactly when the hybrid utahensis forms evolved. But I think it is reasonable to assume that they did so sometime during the late Pleistocene, somewhere in the range of 200,000 to 20,000 years ago, when it could spread across much lower elevations than the 4,000 feet plus heights it requires today.

Indigenous Use of Utahensis

An ancient agave roasting pit in the Spring Mountains.

Human presence in the Spring Mountain area dates to at least 10,000 years ago, and possibly longer. Roasting pits sites used by archaic desert cultures and ancestral Puebloans to cook agave utahensis also contain lithic debris--evidence of the manufacture of rock tools, including mescal knives used to harvest and process agave hearts--have been dated to approximately 7,000 years ago. Agave was one of their most important food sources as big game hunting became more and more difficult because of warming temperatures.

Around 1,000 years ago, the Southern Paiute began moving into the area. Their descendants still live in the here and their oral tradition details their use of agave utahensis. Living a semi-nomadic lifestyle--in the warm valleys during the winter and the cooler mountains during the summer--they travel to their agave sites in the early spring to harvest and cook a. utahensis, often using the same roasting pits that pre-dated them for thousands of years.

Botanists “Discover” Utahensis

From left to right: agave utahensis var Nevadensis, agave utahensis ssp utahensis, and agave utahensis var eborispina.

Botanist George Englemann was the first European researcher to describe agave utahensis in 1871 in Botany of the United States Geological Exploration, 40th Parallel from a sample collected in 1870 in St. George, Utah.

Variety Nevadensis was the next to be formally described in publication by J.M. Greenman and Eva M Roush in 1929 in the Annals of the Missouri Botanical Garden. There they referred to the unpublished notes of Englemann, which labeled a sample collected in 1882 in Ivanpah, California as “A. utahensis var. nevadensis.”

Next up was var. Eborispina, which was first described by botanist J. Pinckney Hester in 1943 in Cactus and Succulent Journal (now called the Journal of the Cactus and Succulent Society of America), from a sample collected at Peak-a-boo Peak in Nevada.

And finally, 7 years later, Kaibabensis was the last of the complex to be described by Susan Delano McKelvey in her 1949 paper A New Agave from Arizona, based on a sample she collected on May 15, 1934, on the Kaibab Plateau on the north side of the Grand Canyon. Earlier botanists had collected and photographed this plant but considered it just to be a “colossal form” of utahensis.

Utahensis Today

A cultivated agave utahensis var nevadensis in a Japanese pot.

Today, agave utahensis is a collector’s favorite and social media celebrity. At some point in the 20th century a Japanese collector successfully propagated an especially wavy spined individual and nicknamed it “kagerou” or “heat haze,” a reference to heat waves that can be seen rising from hot asphalt in the summer. This kick-started a global demand for the plant that has driven up prices and may have led to some illegal poaching of utahensis plants from habitat. I’ve yet to find direct evidence of this practice, but I’m still investigating, and experts assure me the problem is “rampant.”