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The saguaro cactus (Carnegiea gigantea) is a keystone species that grows only the Sonoran Desert of northern Mexico and the southwestern United States. Saguaros produce large, white, fragrant flowers near their crown during April–June, which bloom at night and close the following day.

Over a four-year period, Research Ecologist Daniel Winkler at the Southwest Biological Science Center, in partnership with Saguaro National Park, used historic and current data collected by National Park Service staff, USGS scientists, and community scientist volunteers to understand a phenomenon that was first observed in 1924, but not described, in which saguaro cacti produce flowers in a radial pattern. Their findings revealed that blooms emerge in the east at the beginning of their reproductive season, and continue to flower in a counterclockwise pattern around their stems — the only known flowering plant to do so. 

A key component to collecting data was the use of a collapsible flag pole (referred to as the "world's largest selfie stick") to photograph flowers throughout the spring.

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Flowers first appeared on the east side of all saguaro crowns at the start of the reproductive season, and then spread radially around the crown as the season progressed. And in contrast to previous reports, saguaro flowers were consistently more abundant on the northern part of the crown than in the eastern part.

These novel findings were published in the journal Ecosphere in 2022. This study is the first to document a seasonal, counterclockwise pattern of asynchronous flowering in saguaro, or any angiosperm (flowering plant). Winkler and colleagues are now analyzing the complete dataset to understand the environmental drivers of flowering in the species and predict how saguaros may respond to future climate change.

The study is valuable not only because it helps scientists and land managers better understand this iconic, keystone species but also because it highlights the exciting possibility of new discoveries in biology (even in our own backyards). The study also adds to the many examples of the mathematical beauty of nature, the usefulness of studying under-valued systems including deserts, and that community science can advance our biological understanding of complex systems.

Read the full study:  Foley, T., Swann, D.E., Sotelo, G., Perkins, N., and Winkler, D.E., 2021, Asynchronous flowering patterns in saguaro cacti (Carnegiea gigantea): Ecosphere, v. 12, no. 12, e03873, p. 1-14, https://doi.org/10.1002/ecs2.3873.

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