by Andrea Williams
The Marin Municipal Water District and the California Academy of Sciences recently wrapped up year two of a three-year citizen science project to catalog the plant life of Mt. Tamalpais. In keeping with new tradition, those who participated in the process were invited to a gathering at the Academy. This year, we were also treated to a tour of the herbarium and the process our plants go through after they are collected and squished flat (see photos 1-5 from the tour).
Seeing our specimens added to the Academy’s herbarium reinforced, to me, the purpose of the project: to use this snapshot in time as a way to compare with past and future plant assemblages. The information we contribute is added to the larger pool (or cabinet, in this case) and can be combined, manipulated or extracted to form knowledge. How is the mountain today different from 100 years ago? When did a particular weed show up? Is this the last stand of the tanoak (Notholithocarpus densiflorus)?
Tanoaks are dying off on the mountain from Sudden Oak Death (SOD), caused by the water mold Phythophthora ramorum. I don’t know that tanoaks will be around in another 100 years, if they will disappear from the wild and live on as botanic garden curiosities and herbarium specimens. A study came out this year looking at the pathogen responsible for potato late blight, Phythophthora infestans, which caused the Irish potato famine. To help us understand plant epidemics, the researchers took DNA from herbarium specimens of infested potato (Solanum tubersoum) leaves from the 1840s and sequenced the pathogen, then compared it to modern strains. Like SOD, the pathogen spread quickly and clonally. But it was soon replaced by a separate strain, which is now the dominant type. Unlike SOD, the potato late blight pathogen and its hosts share a similar root and centers of diversity—plant breeders could use the related dwarf wild potato (Solanum demissum), which evolved with P. infestans in Mexico, to breed in resistance to the blight. While there are other species of Lithocarpus in China, where P. ramorum is from, our tanoaks have diverged into a new genus, and their situation is more like the eastern chestnut and its blight—a native tree decimated by a non-native disease.
However it turns out for tanoaks, a portion of their history is now preserved (likely along with the SOD pathogen) in the California Academy of Sciences, along with the hundreds of other plants from the mountain and the millions of plants in the Academy’s collections; history that will be accessible and shared with researchers for decades or centuries to come.