Vibrant green with lustrous leaves in the Spring, Poison Oak (Toxicodendron diversilobum) generally becomes less vivid with age, eventually turning red in the late Summer and Fall. The red color is due to anthocyanin pigments in the plant’s sap that become unmasked as the leaf loses chlorophyll.
Anthocyanin pigments are responsible for the reds and purples in Autumn leaves, and in common fruits and vegetables such as apples, plums, cranberries, grapes, tomatoes and strawberries. Some studies suggest anthocyanin pigments may contribute to the health benefits of these foods.
While the chemistry of Fall colors is fairly well understood, the role the yellow and red pigments play in the physiology of plants is not as clear. In The Warm Hues of Fall Foliage (2002), Geoff Brumfiel summarizes competing theories, ranging from sun and frost protection to acting as a bug repellent — or attractant.
As a starting point for more information regarding poison oak and it’s allergen urushiol, see Poison Oak: More Than Just Scratching The Surface (Wayne’s Word) and Allergies: Poison Plant Allergies: Poison Ivy, Oak, and Sumac (WebMD).
The photograph of poison oak is from a run in Dayton Canyon in the Simi Hills northwest of Los Angeles.
Related post: Poison Oak Along the Garapito Trail
Sylvan Hairstreak (Satyrium sylvinus) on California Goldenrod (Solidago californica) at Sage Ranch Park.
In late September 2005, the Topanga Fire burned many thousands of acres in the Simi Hills. One of the side effects of the fire was to reveal the extent of the refuse that was in the creek bed that runs east-west between Boeing’s Santa Susana Field Laboratory and Sage Ranch Park.
The rusty storage drum in the photograph above is just one of several drums and other refuse I saw partially buried in the sediments of the creek.
These photographs are from a run at Sage Ranch on October 21, 2005. In March and April 2006 some restoration and other environmental work was done in this area, and some of the refuse pictured may have been removed. The area is recovering from the fire, and the section of the creek bed pictured is now so overgrown it is difficult to tell.
This topographic map shows the location of the creek relative to Sage Ranch and Rocketdyne, and (in red) the Sage Ranch loop trail. The creek is part of the Meier Canyon drainage, which flows into Simi Valley.
Here are some additional sources of information regarding environmental issues in the area:
Department of Toxic Substances Control Santa Susana Field Laboratory Site Investigation and Cleanup Web Site
Department of Toxic Substances Control Project Documents: Santa Susana Field Laboratory
Boeing: About Us – Environment – Santa Susana Field Laboratory
Wikipedia: Santa Susana Field Laboratory
A bracket fungus (prob. Laetiporus gilbertsonii) on a burned eucalyptus in the Simi Hills.
A native of the Mediterranean, Milk Thistle is an invasive weed that appears to be increasingly profuse in roadside areas of Upper Las Virgenes Canyon Open Space Preserve. Generally considered detrimental in the wild, the plant has been used medicinally for at least 2000 years, and is cultivated in Texas, Canada and Argentina.
According to the Washington State Noxious Weed Control Board, Milk Thistle (Silybum marianum) produces about 190 seeds per flower, and over 6000 seeds per plant. Dense stands are reported to produce 1.4 million viable seeds and four tons of vegetation per acre! Here is a closer look at an individual Milk Thistle seed.
This photograph was taken on a run at Ahmanson Ranch on July 13, 2006. The posting Convoluted includes a photograph of the white-veined leaf, and a photo of a dense stand of Milk Thistle in Las Virgenes Canyon. Additional information regarding Milk Thistle, including its history, laboratory studies, clinical trials, and adverse effects can be found in the National Cancer Institute’s Milk Thistle (PDQ®).
Cucumber Beetles (Acalymma trivittata) munching on the pistillate blossom of the wild gourd Calabazilla (Cucurbita foetidissima). The photograph is from Sunday’s Ahmanson-Cheeseboro run.