In early May, botanists Christopher Thayer and Heath Bartosh walked transect lines at Rockville Trails in Solano County in search of western viburnum, a rare shrub never before documented in the county. Some theorize that viburnum is a relict of the last ice age, says Bartosh, and that the plant was widespread in lower latitudes until the glaciers retreated. “They started to wink out,” says Bartosh, “until they found a niche in deep-shaded, north-facing aspects.”
Thayer and Bartosh are assembling a Solano flora (a definitive key of this particular region’s plants) and are in year three of what they predict will be a 10-year project. It is the first for the county even though Willis Linn Jepson, the father of California botany, was born in Vacaville, and he botanized here as a boy. Jepson wrote the first flora of California, The Manual of Flowering Plants of California, and is the namesake of the Jepson Manual, a compiled flora for California that Thayer and other botanists consider their bible. A revised Jepson, 10 years in the making, was released in January 2012 with a large number of classification changes based on genetic analysis.
Thayer and Bartosh had reason to believe they would find the rare plant at Rockville Trails because it had been listed in a study for a housing development once proposed here. Bartosh says he saw the plant at the “magic hour, when shadows are long, and the landscape gets that golden feeling.” He found 20 blooming plants along the margin of an oak woodland.
A viburnum specimen will be placed in the University and Jepson Herbaria of the University of California at Berkeley. “Finding and collecting western viburnum in Solano County is a significant documentation on a statewide basis for a very rare native shrub,” says Thayer. It’s also just one plant of the many that they will document for the flora, and one more reason to help Solano Land Trust protect Rockville Trails. Learn more about Rockville Trails at solanolandtrust.org/SaveRTE.aspx or the flora project at email@example.com.