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Modified 26-Mar-24
Created 29-Aug-21
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This is the final "Wildflower" talk this season, sponsored by the Nature and Science Committee of the Town of Portola Valley. In this warm dry season, given the sparsity of new wildflowers, I focus on the local oaks growing in Portola Valley.
Our local oaks belong to two lineages: the White Oaks (Valley, Blue, and Leather Oaks); and the Red Oaks (Coast Live Oak and Black Oak). Each lineage hybridizes only with others in the same lineage. Only the Red Oaks are susceptible to Sudden Oak Death. Each lineage contains both evergreen and deciduous species.
One favorite tree, with large individual specimens, is our Valley Oak. It is seasonally deciduous: losing its leaves according to the season and the amount of sunlight.
The Blue Oak is drought deciduous, losing its leaves in response to the availability of water. It is also the one most tolerant of the lack of water, almost able to go into suspended animation until sufficient water reappears. Blue Oaks often grow in woodlands, many trees all together.
The Leather Oak only grows in our serpentine soils. These soils are deficient in some plant nutrients, and have other chemicals that make it difficult for plants to grow. They have thus formed as a refuge for our native species, as European invaders sweep across the state. (The invaders are evolving the ability to tolerate serpentine soil, however, as nitrogen deposition from our cars' catalytic converters supplies some of the missing nutrients.) In this impoverished soil, Leather Oaks often remain small, bonsai-like, even at an advanced age.
The most prominent of the Red Oaks is our Coast Live Oak. Yes, it is "live", evergreen. Its tough leaves sport spines to keep browsing deer at bay. And as the young plants grow, their width eventually keeps deer from reaching the center, allowing a shoot to escape and rise up to form a tree: natural topiary.
The last oak I feature is the Black Oak, also in the Red Oak lineage. Black Oaks tend to grow at higher elevations in Portola Valley; in the fall, you can sometimes see a band of yellow or red across our hillsides, where deciduous Black Oaks predominate. Black Oaks are a feature of Yosemite Valley.
Though I found no prominent new wildflowers out this month, there are a few holdovers from previous months. Here are photos of fragrant Hayfields Tarweed; Green Everlasting; Birch-leaf Mountain Mahogany; and Wild Rose. Much of the color of this season does not come from true flowers, with their pollen and nectar to lure insects, but from seeds ready to spread, and colorful leaves. Only the tarweed and rose are true flowers.
My bonus for this final presentation is some photos of grinding mortars left by the local Native Americans. While they certainly did grind and eat acorns, they had a varied diet, tending many plants and plant communities to assure continued production.
