What it means
Brittlebush is the most common shrub on a Scottsdale hillside that is not creosote: a tidy, rounded mound of silver-gray leaves, knee to waist high, that looks dusty for ten months and then, for a few weeks in spring, holds up hundreds of bright yellow daisies on long bare stems. When locals say the hills are yellow in March, this is the plant they mean, and the desert plants field guide names it as the reason.
The silver is the clever part. The leaves are coated in dense white hairs that reflect sunlight and keep the leaf cool, and the plant grows a smaller, hairier set of leaves for summer than it does for the wet winter. In a bad drought it drops them all and waits.
You will hear the word from a hiker in spring (“the brittlebush is going off on Tom’s Thumb”) and from a nursery, where it is the cheap, fast answer to a bare slope.
Where you’ll meet it
Everywhere rocky and sunny: the slopes of the Preserve, especially the old burn around the Tom’s Thumb trailhead; freeway shoulders, where it is planted for restoration; the Xeriscape Garden. It also names a golf-clubhouse pub at Kierland, Brittlebush Bar and Grill.
Where the word came from
The English name is plain description: the stems are brittle and snap at a touch. Nobody has claimed coining it. The older name is Spanish, incienso, incense, because early Spanish missions in the New World burned the plant’s dried resin in place of frankincense. The resin oozes from the stems as golden beads and smells sweet and sharp when warmed.
The peoples who were here first had more uses for it than the missions did. Two kinds of resin come off the plant: a darker one near the base and a clearer, gummier yellow one on the upper stems. The Seri used the gummy resin to seal pottery, and both the O’odham and the Seri used it to haft points to arrows and harpoons; resins also served as varnish and waterproofing and as remedies for toothache. The botanical name, Encelia farinosa, means floury Encelia, for the mealy white coat on the leaves.
The Scottsdale chapter is about fire. In 1995 the Rio fire burned about 5,000 acres of what is now the Preserve, from Fraesfield Mountain south to Windgate Pass, including the East End and Tom’s Thumb. The McDowell Sonoran Conservancy’s survey found those slopes now covered primarily with brittlebush, a shrub that thrives on disturbed ground. The yellow hills hikers photograph above the Tom’s Thumb lot are, in part, a 30-year-old burn scar recovering.
What it is not
Not creosote, which is green, taller and smells of rain. Not a wildflower in the strict sense either: brittlebush is a perennial shrub that blooms every spring it gets enough rain, while poppies and lupine are annuals that appear only in good years. In a superbloom they share the hill.
The fine print
The Forest Service’s species review puts numbers on what locals see. Flowering follows at least about 20 millimeters, roughly three-quarters of an inch, of cool-season rain plus enough warm days afterward, and the share of plants that bloom swings from none to all of them depending on the winter. Average lifespan in the northern Sonoran Desert is about 16 years; the oldest recorded plant, in an area protected from grazing, reached 72. Frost sets its northern and upper limits: a hard freeze, around 23 degrees Fahrenheit, can strip a plant of every leaf, which is why yard brittlebush looks dead after a cold January and fine by March.
Fire is double-edged. Brittlebush usually comes back quickly after a burn and is often more abundant afterward, as the Preserve shows. But fires carried by invasive buffelgrass kill it at higher rates than fires in native annual grasses, and recovery depends on rain in the seasons after the burn.
Its leaves contain a growth inhibitor, 3-acetyl-6-methoxybenzaldehyde, that, by the Forest Service’s account, may inhibit seedlings and kill young plants nearby; it may help explain why brittlebush stands look evenly spaced. In a garden, do not expect seed sown right underneath to thrive. Give it full sun, rocky soil and little water, cut it back after bloom if it gets leggy, and let it do the one thing it does better than anything else on the hill.