Mistletoe is a hemi-parasitic plant, meaning that it draws some, but not all, of its nutritional requirements from its host plant. They attach to the host plant through its haustorium, the root-like structure that penetrates into the host’s vascular tissue to slurp up water and sugar. Infections can be so bad that they can kill the host tree, either by drawing too much from the host plant or by outcompeting the foliage of the host, practically replacing all of the growth but in most circumstances mistletoe adds complexity and diversity to our forests.
There are over 1,300 species of mistletoe worldwide, and California is home to many native species, including the oak mistletoe, American mistletoe, western dwarf mistletoe, Douglas fir dwarf mistletoe, and fir dwarf mistletoe. Some of their names suggest their preferred host, others are more generalist, like the American mistletoe that can infect ash, alder, oak, willow and more. Despite being a numerous and varied species, the physical form of mistletoe is generally similar: evergreen leaves and white fruit. California is now home to some invasive mistletoes as well, including the European mistletoe.
Given that mistletoe co-evolved with the wildlife of California, it comes as no surprise that mistletoe plays an important role in forest ecosystems. Mistletoe brooms provide an excellent structure for nesting birds, including the northern spotted owl and marbled murrelets, which appears to have a particular fondness for the dense foliage–so much so that 90% of owl nests in Southwest Oregon are reported to be in mistletoe.