Updated: Oct 14, 2022
In the southern woodland canyons of California, you are likely to come across two particularly interesting plant species that are native to the region. These species are the Pacific Poison Oak (Toxicodendron diversilobum) and the California Mugwort (Artemisia douglasiana). These two plant species are often found in close proximity to each other in a variety of habitats across the Western United States, but favor the oak woodlands and riparian habitats. The plants within California’s oak woodlands have adapted to a unique Mediterranean climate, and to wildfires that occur seasonally. The frequency of wildfires aid the vegetation in this habitat and help in its growth. However changes in climate can bring more intense wildfires, leading to some changes in how these species thrive. Oak woodlands are near but not necessarily adjacent to water sources, whereas riparian habitats are found directly adjacent to a water source- such as a river, lake, estuary, or streambank. Riparian means living or located on the bank of a natural watercourse, such as a river or sometimes a lake. Riparian habitats are considered a transitional zone between terrestrial and aquatic systems, making its native plants directly shaped by the presence of water. Adaptations include their ability to filter out excess nutrients and stabilize the sediments to help decrease land erosion.
Diagram showing the connection between riparian and woodland zones as the habitats change the farther from water they go. Credit: Oliver & District Heritage Society.
Pacific Poison Oak, also known as Western Poison Oak, is a perennial deciduous shrub that grows quickly in the early winter months and has its blooming season from April to June. Perennials are plants that continually grow each year and do not die after they have bloomed. Deciduous shrubs are plants that shed their leaves during a certain season or development stage in their life cycle. For poison oak, that is typically in the late summer and early fall. Many plants in California are deciduous and drop their leaves during the summer to preserve their energy in the dry months, these plants are called drought deciduous.
New leaves on Pacific Poison Oak will be shiny with a red tint, maturing into a shiny green during the summer, and finally turning into a yellow or bright red before dropping in the fall. Credit: Poison-Ivy.org
It is important to note that, while they are in the same family, poison oak is different from poison ivy with regards to their locations and plant structure. However, both plants are known for their toxic effects on humans when exposed to the leaves. Poison oak is known for its allergen urushiol, an oil that excretes from the leaves and causes contact dermatitis (a strong, maddeningly itchy rash, leading in a couple of weeks to blisters which can spread by contact to other areas of the body) when touched or brushed up against. For this reason, it is very important to be able to identify the plant and steer clear from it when hiking in our natural environment. Poison oak becomes even more dangerous when burned as inhaling the smoke can cause severe lung issues.
With all that said, one may not see a benefit to Poison Oak. But, just because it can harm us, does not mean it is harmful to the rest of the environment. Interestingly enough, Poison oak serves a multitude of benefits and uses for native wildlife as the urushiol oil does not negatively affect them. The leaves of the plant are enjoyed by the black-tailed deer for grazing and the berries are enjoyed by smaller mammals and birds, such as the California towhee. The plant as a whole also serves as shelter for small mammals and birds. In past research, the federally endangered least Bell’s vireo was found using poison oak plants in oak woodlands as nest sites. In conclusion, while poison oak might scare us, the plant is very important for other native wildlife, contributing to biodiversity and a healthy ecosystem for oak woodlands.
Unaffected by the urushiol oil, small mammals and birds will be seen enjoying the leaves and berries of both Poison oak and Poison ivy. Credit: Gary P. Bell
If you have ever had an unfortunate encounter with poison oak, there is a high chance you also encountered the plant known as California Mugwort! Even if you were unable to identify it, California mugwort (also known as Douglas's sage/mugwort) is commonly found growing nearby or directly next to poison oak. California mugwort is an herbaceous perennial forb native to the western United States and grows in Riparian habitats. A relative to California Sagebrush, the plant grows in upright strands and blooms between the months of May to October. The sturdy stems of the plant protects underlying soil from erosion, which allows mugwort and other riparian plants to thrive along the streambanks. In Riparian habitats, mugwort seeds are foraged by a handful of native birds and its leaves can be used as nesting material for some bees.
Credit: Plant Material
California Mugwort provides an abundance of helpful uses for humans- most known for its medicinal uses. Even more interesting, mugwort is considered an antidote against the rash caused by urushiol oil from poison oak and works best when applied to the exposed skin directly after contact with the allergen. Native Americans (the Chumash tribe) ground fresh mugwort leaves between the hands and rubbed the crushed plant matter onto the affected area. Another way was boiling fresh leaves to make a tea, which was applied to the rash or sometimes consumed. Mugwort was and is still used today for relieving joint pain, headaches, and can sometimes be used to treat female reproductive issues. It is important to note that there is still more research needed to be done in the effectiveness of using mugwort and if there is any harm in using large quantities of the plant. While some plants can be beneficial to our health, remember to consult a doctor before practicing any new home remedies.
California Mugwort holds cultural significance as it was sometimes used for physical and mental healing by Native Americans. Credit: GardenTags
Pacific Poison Oak and California Mugwort are two very different plants that each play a crucial part in their respective habitats, but also in our lives as humans. They each provide a number of benefits to us and the native environment, while also having an interesting relationship in one being the antidote to the other. They serve as vital plant species for the overall ecology of Southern California. The next time you are hiking through these habitats, see if you can spot these two incredible species yourself!