by Roseann Hanson, Art and Science Program Coordinator 

A wave of yellow is washing up the slopes of Tumamoc . . . our spring harbinger, the brittlebush (Encelia farinosa). Since early February, I have been sketching the floral sequence: buds, then the first rays, and now the more fully emergent flowers heads unfurling.

As I sketched and studied the flower buds and leaves, I noticed that the younger leaves are more greenish-yellow, where the more mature leaves become the classic silver-blue, most likely because of the dense fuzz on their surface (during hot and dry times of the year, they also appear more silver-blue; the dense fuzz helps conserve moisture and provide protection from sun). The plants around the lab buildings and farther up the hill are blooming for robustly—most likely because they received more rain.

Brittlebush is a signature plant of the Sonoran Desert, thriving along washes, roadsides, desert flats, and up hillsides, to 3,000 feet. They will bloom from March through June, though I’ve seen a few opportunists bloom most months of the year if a good rain and enough warm days pass.

And does anyone else see a Fibonacci spiral in the tiny disc florets that make up the flower center? (Brittlebush have ray florets—the long yellow ‘petals’—and a center made up of tiny disc florets.)

Left: a sketch of the Fibonacci’s geometry. Right: agave leaves show Fibonacci spiral growth patterns.

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Within a week or so, given a bit more warmth and sunny days, we should be seeing a full tidal wave of yellow washing up our Hill.