Healthy greasewood—dig here! (photo by Cory Maylett)
While traveling up the Missouri River through today’s northeast Montana, the great American explorer Meriwether Lewis came upon a shrub he didn't recognize, growing in large stands. "Hereafter I shall call it the fleshey leafed thorn” he wrote in his journal, on May 11, 1805. Lewis didn’t much like it, noting it was “extremely troublesome” and that animals avoided it (source).
“Fleshey leafed thorn” with succulent leaves, sharp-tipped twigs, and red winged fruit. It's now called greasewood (photo by Jim Morefield).
For the most part, folks agree there’s little to like about greasewood, including its eponymous habitat—wet greasy mud, where vehicles slide around before becoming firmly stuck. The scientific name, Sarcobatus vermiculatus, means fleshy bramble of small worms. Indeed, greasewood branchlets develop into stiff sharp painful spines, and the succulent leaves look like little green worms. And they’re toxic, fatal to any livestock that eat them. For greasewood grows where water is bad—salty, alkali, poison.
Many desert basins in southern Wyoming are closed—water runs in but not out, ponding at low points. Some soaks into the heavy soil, but much evaporates, leaving behind whatever chemicals were carried in—sodium, potassium, magnesium, calcium, and sometimes weird nasty things like boron and mind-altering selenium. Salty crusts encircle wetlands. When lakes dry up, brilliant white playas remain.
Amazingly, greasewood appears to thrive on these harsh sites! On basin margins it grows mixed with other salt-tolerant species, but on the chemical-rich heavy soils of the lowlands, it forms pure stands where few other plants can survive.
Alkaline and saline soils present insurmountable challenges to most plants, because their roots can’t absorb water with high concentrations of solutes (dissolved chemicals). But greasewood is a halophyte—a “salt plant.” The root cells contain high concentrations of solutes, and take up water even in these difficult situations. Greasewood stores toxic salts (oxalates) in its succulent leaves, and being deciduous, disposes of them at the end of the growing season, making the soil below especially salty.
Greasewood flat in southern Wyoming, by Dan Lewis, The Wyoming Naturalist. Used with permission.
Greasewood leaves, to 4 cm long (NPS).
From Meinzer 1927.
• • •
Let’s walk down into a closed desert basin to a healthy stand of pure greasewood in the very bottom, and start digging.
First we have to get through heavy fine soil laced with small roots—there to absorb any water that might soak in. The networks can be dense. Donovan and colleagues (1996) found 140 km of roots per cubic meter under greasewood canopies!
Next, we dig through fine roots for several feet while navigating around substantial lateral roots 3 to 12 feet long. These are equipped with adventitious buds that send up shoots (clones) when a plant is damaged. Burned or cut plants can crown-sprout as well. No wonder the US Department of Agriculture warns land managers to leave greasewood stands alone:
“… treatment of the site will most likely fail or be a very poor investment of capital. … Areas of black greasewood that are burned, crowned, brush beat, or shallow plowed and/or shallow disked will often result in a much higher density of black greasewood. … Thus extreme caution should be exercised when selecting which sites have the best potential for improvement.” (“treatment” and “improvement” mean eradication; more details here)By the time we’re six feet below the surface, we’ve left behind the fine roots, lateral roots and developed soil. But the tap root continues on. And it’s large—several inches in diameter:
“Near Moab, Utah, along a creek where the water had cut away the bank, exposing the roots, a greasewood 6 feet tall had roots down 18 feet, a taproot 3 inches in diameter down 6 feet, and abundant feeding roots, some 10 feet long, at a depth of 10 to 12 feet.” (Shantz 1940)How far do we have to dig to find the tap root’s end? Usually at least 10 to 15 feet, often 20 or 30 feet, and sometimes more:
“Near Grandview, Idaho, H.T. Sterns observed roots of greasewood penetrating the roof of a tunnel 57 feet below the surface.” (Meinzer 1929; italics added)Finally the tap root reaches its destination—the blessed capillary fringe! Here root hairs absorb sweet water that has seeped up from the water table. It's sucked up the tap root 10, 20, maybe even 50 feet—whatever it takes to reach the thirsty greasewood plant, standing in hot sun on an alkali mudflat.
“These plants have been called phreatophytes. The term is obtained from two Greek roots and means a ‘well plant.’” (Meinzer 1927; arrow added).
Old timers knew that a healthy stand of greasewood meant sweet water wasn't all that far away. They knew greasewood could help them site wells. But it wasn’t until the early 1900s that ecologists and hydrologists were convinced:
“Greasewood was not at first regarded as an indicator of ground water, because to a large extent it grows on land that lies some distance above the water table. Information now at hand, however, makes it practically certain that greasewood habitually sends its well-developed taproot to considerable depths … It is, thus, one of the most trustworthy of all ground-water indicators.” (Meinzer 1929; italics added)
Prickly, toxic and hardly photogenic, greasewood is helpful too—a most trustworthy groundwater indicator (photo courtesy BLM).
Sources (in addition to links in post)
Donovan, LA, and colleagues. 1996. Water Relations and leaf chemistry of Chrysothamnus nauseosus ssp. consimilis (Asteraceae) and Sarcobatus vermiculatus (Chenopodiaceae). Amer. J. Bot. 83: 1637-1646.
Groeneveld, DP. 1990. Shrub rooting and water acquisition on threatened shallow groundwater habitats in the Owens Valley, California in Proceedings: symposium on cheatgrass invasion, shrub die-off, and other aspects of shrub biology and management. Available here.
Knight, DK, and colleagues. 2014. Mountains and plains; the ecology of Wyoming landscapes, 2nd ed. Yale University Press.
Meinzer, OE. 1929. Plants as indicators of groundwater. USGS Water Supply Paper 577. Available here.
Shantz, HL, and Piemeisel, RL. 1940. Types of vegetation in Escalante Valley, Utah, as indicators of soil conditions. Tech. Bull. 713. Washington, DC: US Department of Agriculture. 46 p. Available here.
USDA NRCS Plant Guide: Black Greasewood.