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C. Hart Merriam, an American zoologist and ethnographer who studied the plant life around the canyon in 1889, grouped the species here into geographical ranges that he called "life zones." According to Merriam, different life zones resulted from "laws of temperature control" that corresponded to elevation change. Each life zone began and ended at a particular elevation, much like the rock layers that ring the canyon walls.

Merriam's theory was a good one at the time, but he didn't immediately recognize the significance of other variables. Today, naturalists understand that the Grand Canyon's flora is strongly affected by factors such as air currents, water flows, soil types, slope degree, and slope aspect (the orientation of the earth's surface in relation to the sun). Most naturalists now prefer to talk about "biological communities," avoiding the mistake of fixing species in any particular zone.

However, if your goal is to identify a few major plant species and the general areas in which to find them, life zones still work fairly well. So we'll use them, with thanks to Dr. Merriam. The canyon's five life zones are: boreal, from 8,000 to 9,100 feet; transition, from 7,000 to 8,000 feet; upper sonoran, from 4,000 to 7,500 feet; lower sonoran, from the bottom of the canyon to 4,000 feet; and riparian, along the Colorado River's banks and tributaries. Some of the more common or unusual plants in each zone are as follows:

Boreal Zone

Blue spruce -- The magnificent blue spruce, sometimes called the Colorado spruce, is native to the Western U.S. and grows at elevations of 5,900 to 10,000 feet. It is one of the most popular evergreens, even showcased as the national Christmas tree each year in Washington, D.C. It has silvery to blue-green needles, blooms in April and May with 3-inch cones, and grows 50 to 75 feet high, with a full spread of 25 feet at maturity.

Douglas fir -- Found on the North Rim (most often close to the rim itself) and on isolated north-facing slopes below the South Rim, this tree grows up to 130 feet high and 6 feet in diameter. Its hanging cones, which grow to about 3 inches long, have three-pronged bracts between their scales. Each of its soft needles is about 1 inch long. The Douglas fir is built for cold weather; its branches, while cupped, are flexible enough to slough off snow.

White fir -- You'll know you've moved into spruce-fir forest when you start tripping over deadfall and running into low branches. One of the more common trees in this high-alpine forest, the white fir has smooth, gray bark. Its cones grow upright to about 4 inches long, and its 2-inch-long needles curve on two sides. The white fir closely resembles the subalpine fir. But the subalpine fir's branches, unlike those of the white fir, grow to ground level, and its needles are about an inch shorter.

Transition Zone

Big sagebrush -- More common on the rims than in the canyons, this fuzzy gray-green shrub grows to 4 feet high on thick wood stalks. To make sure you haven't misidentified it as rabbit brush (another gray-green plant of comparable size), look at a leaf -- it should have three tiny teeth at the end. Or simply break off a sprig (outside the park) and smell it. If it doesn't smell divine, it's not sagebrush. Some Native American tribes burned sage bundles during purification rituals.

Gambel oak -- To find Gambel (or scrub) oak on the South Rim in winter, look for the bare trees. The only deciduous tree in the South Rim's immediate vicinity, its leaves turn orange before falling. To find Gambel oak in summer, look for its acorns, its long (up to 6 in.), lobed leaves, and its gray trunk. It grows in thick clumps that clutter the ponderosa pine forest's otherwise open floor. A plant with a similar name, shrub oak, grows lower in the canyon and has sharp, hollylike leaves.

Indian paintbrush -- You should be able to identify this rare plant from the name alone. Many of its flower-like bracts are colored red or orange at their tips, making them look as if they've been dipped in paint.

Lupine -- Common on both rims, this flower blooms from spring to late summer. You can spot lupine by its palmate leaves and tiny purple flowers growing in clusters at the top of its main stem.

Ponderosa pine -- Found on both rims and in isolated places in the canyon, this is the park's only long-needled pine. It dominates the forest at elevations between 6,000 and 9,000 feet, can live 120 years, and reaches heights of 100-plus feet. The ponderosa pine can also withstand forest fires (provided the fires come often enough to keep flammable brush on the forest floor to a minimum); its thick bark shields the inside of the tree from the heat. And once the tree's low branches have burned off, fire can no longer climb to the crown. So the trees that survive grow stronger. When the fires are over, they thrive on the nutrients in the ash-covered soil. Mature ponderosa pines have thick red-orange bark (younger ones have blackish bark), 6-inch-long needles in groups of three, and no low branches. Once you've identified one, smell its bark -- you'll be rewarded with a rich vanilla-like scent. This tree provides shelter for the Kaibab and Abert squirrels.

Quaking aspen -- The ponderosa pine may smell better, but tree-huggers should save the last dance for the quaking aspen, which grows alongside it in many North Rim forests. Its cool, dusty white bark feels great against your cheek on a hot day. Its green, shimmering leaves -- on long, twisted stems -- shudder at the very idea of a breeze, creating the impression of a tree that's "quaking" in the wind. If you hug one aspen, you're probably hugging many: Dozens and sometimes hundreds of these trees have been known to sprout from a common root system, meaning they're technically one plant. In fact, one of the world's largest organisms is a quaking aspen in Utah.

Upper Sonoran

Cliff rose & Apache plume -- These flowering shrubs, which grow on both the rims and in the canyon, have much in common. Both are members of the rose family, grow tiny five-lobed leaves, and send up numerous delicate flowers from which feathery plumes sometimes protrude. However, a few differences do exist: Cliff rose is larger, growing up to 25 feet, compared to 5 feet for the Apache plume. The cliff rose's blossoms give way to seeds whose white plumes allow the wind to scatter them some distance. The flowers are a creamy yellow, as opposed to white for the Apache plume. And its leaves, unlike those of the Apache plume, are hairless. The Apache plume blooms a few weeks longer -- from early spring into October.

Mormon tea -- Common throughout the park, this virtually leafless plant has hundreds of jointed, needlelike stems that point skyward. Once the plants are full-grown, they remain largely unchanged for as long as 500 years. Photos of desert scenes taken more than 50 years apart show the same Mormon tea plants with every stem still in place. The only difference between young and old plants is their color -- the more ancient plants are yellow-green or even yellow-gray; younger ones are light green. The early Mormon pioneers and the Native Americans used the stems, which contain pseudoephedrine and tannin, for medicinal purposes.

Piñon pine -- Wherever a new juniper tree sprouts, a piñon pine usually takes root in its shade (junipers are more heat-tolerant), growing to about the same size (30 ft.) as the juniper. Shorter and rounder than most pines, the piñon grows 1-inch-long needles, usually in pairs, and often lives more than 2 centuries. Together, the piñon pine and the Utah juniper dominate much of the Southwest's high desert. Piñon (or pine) nuts, packing 2,500 calories per pound, have always been a staple for Native Americans in this area. Now they're also popular in Italian restaurants, where they're used to make pesto.

Utah agave & banana yucca -- The plants consisting of 3-foot-long spikes are most often agave or yucca. Agave leaves have serrated edges, while yucca leaves have rough, sandpaper-like sides. Native Americans used these plants' fibers and leaves to make sandals, baskets, and rope. If you were to break off a particularly sharp leaf and peel away the fibers from its edge, you would eventually end up with just a thread with a needlelike tip. The agave blooms only once every 15 to 25 years. When it does, it's easy to spot -- its spiky base sends up a wooden stalk, about 14 feet high, atop which yellow flowers grow. Because this flourish occurs so rarely, the agave is often referred to as the century plant. After flowering, it dies. Some naturalists theorize that the agave, whose leaves become rich in nutrients just before it flowers, evolved to bloom rarely so that animals would not grow accustomed to eating it. This trick didn't fool the Ancestral Puebloans, who discovered that the roasted hearts of the plant were always nutritious. Unlike the agave, the banana yucca, one of the Southwest's most common and useful plants, blooms every 2 to 3 years, sending up 4-foot-high stalks off which yellow flowers hang. Its fruit, which tastes a bit like banana, ripens in late summer.

Utah juniper -- This tree, which seldom grows higher than 30 feet, looks as though it belongs in the desert. Its scraggy bark is as dry as straw, its tiny leaves are tight and scalelike, and its gnarled branches appear to have endured forever. Burned in campfires since the dawn of time, juniper wood releases a fragrant smoke that evokes the desert as much as the yipping of coyotes. Its dusty-looking blue berries are actually cones, each with one or two small seeds inside. Juniper is a traditional flavoring for game meats and for gin.

Lower Sonoran

Barrel cactus -- The barrel cactus does indeed resemble a small, green barrel. One of the more efficient desert plants, it can survive for years without water. Contrary to the popular myth, however, there's no reservoir of drinking water inside.

Blackbrush -- The Tonto Platform's blue-gray color doesn't derive solely from the Bright Angel Shale. It also comes from blackbrush, a gray, spiny, 3-foot-high bush that dominates the flora atop the platform. Blackbrush grows leathery, half-inch-long leaves on tangled branches that turn black when wet. Because the plant's root system is considerably larger than the plant itself, each one commands plenty of area; there are usually 10 to 15 feet between blackbrush plants.

Hedgehog cactus -- The hedgehog cactus looks like a cluster of prickly cucumbers standing on end. Of the four species in the canyon, the most colorful is the claret cup, which sprouts crimson flowers every spring.

Honey mesquite & catclaw acacia -- These two tree species, which favor the walls above rivers or creek beds, show us the heights reached by the Colorado River's predam floods. After a flood recedes, mesquite and acacia seedlings take root in the moist soil. Later, the maturing trees send pipelike roots down to the river or creek bed. Both species, which have dark branches and leaves with small paired leaflets, reach heights of about 20 feet, and grow seedpods several inches long. The mesquite's leaflets, however, are longer and narrower than the acacia's. And while the acacia has tiny barbs like cat claws for protection, the mesquite grows paired inch-long thorns where leaves meet the stems. Mesquite beans were a staple for the Ancestral Puebloans.

Opuntia cactus -- Most members of this family are known as prickly pear. Although prickly pears do grow on the South Rim, the most impressive are lower in the canyon. There, the prickly pear's flat oval pads link up in formations that occasionally sprawl across 40 or more square feet of ground. Look closely at each pad and you'll notice that, even in the most contorted formations, the narrow side always points up, reducing the amount of sunlight received. Because this cactus tends to hybridize, it produces a variety of yellow, pink, and magenta flowers from April to June. Put a finger inside one of these flowers, and the stamens will curl around it, a reflex designed to coat bees with pollen. This plant's cactus pads can be roasted and eaten (once its spikes are removed), and the fruit, which ripens in late summer, is edible, too; it's often used to make jelly. There are several opuntia species, ranging from very prickly (grizzly bear) to spineless (beavertail).

Riparian

Fremont cottonwood -- To cool off in the shade, look for this tree's bright green canopy, which grows near many of the Colorado River's tributaries but seldom by the large river itself. The tree's spreading branches and wide, shimmering leaves shade many of the canyon's springs. Its trunk, covered with grooved, ropelike bark, can grow as wide as a refrigerator. Its flowers, which bloom in spring, drop tiny seeds that look like cotton and can ride breezes to distant water sources. A nice grove of these trees shelters the picnic area at Indian Garden.

Tamarisk -- The CCC once used this exotic species for flood-bank control. Today, it is the plant that boaters and hikers love to hate. Before Glen Canyon dam was built, the Colorado River's annual spring floods thinned or wiped out most of the tamarisk along its banks. Now, tamarisk and coyote willow have taken over many beaches, creating thickets that can make hiking miserable. Other animals don't mind the thickets; they're home to a diverse population of birds, lizards, and insects. Soft as ostrich feathers, the plant's stems grow tiny, scalelike leaves and sprout small, white flowers in spring. While young tamarisk consists of skinny, flexible stalks, older plants have wood trunks.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.