Wildlife of the James - Presquile’s Parasitic Plants

By Zack Lake,  JRA Field Educator

It’s the Halloween season, so here’s a plant that would make any vampire happy! Walking along the boardwalk at Presquile National Wildlife Refuge, if you look just to the left facing the creek, you will come across dodder, one of the 4,100 known species of parasitic plants. Dodder (Cuscuta sp.) is a genus of yellow, orange, or red parasitic plants which is comprised of 100 to 170 different species, only 9 of which have been identified in Virginia.

While certain species of dodder are capable of photosynthesis, other species are obligate parasites. This means it must have its host to survive and complete its life cycle. A host is needed because many species of dodder lack leaves and chlorophyll entirely, hence the yellowish coloration. The plant is rather inconspicuous, and appears as a thin yellow string. To compensate for its lack of chlorophyll, dodder penetrates the host plant with modified root structures known as haustoria, inserts itself into the vascular system of the host plant, and extracts carbohydrates. Although dodder can be germinated without a host, it has to reach a plant quickly to survive.

Here’s the fascinating part that makes this parasitic plant even creepier: dodder seeks a viable host through the use of airborne volatile organic compounds (VOCs) and then grows toward these cues to reach its host! To put that into simpler terms, the plant actually seeks out and finds its host by sense of smell. Like any good vampire who wants a meal, it is not advantageous for dodder to kill its host plant, and infestation is generally not deadly to the host plant, though infestations may prove fatal if severe enough.

While certain species of dodder are host species-specific, meaning that they can only grow on a particular species, most dodder species can grow on several different types of plants. Some host plants include Spotted jewelweed, Goldenrod, Black locust, and Blackberries. Even though it is a parasitic plant, dodder has such a seemingly relentless strategy for survival that it can actually be beneficial to plants other than the host. For example, dodder can control the growth of fast-spreading plants such as Virginia creeper and English ivy, which can often crowd out other plants. Dodder is an annual plant that spreads through seed dispersal. And it is extremely patient! Dodder’s seeds have a very hard coat and can remain dormant for as long as 5 to 10 years. Happy Halloween from Presquile National Wildlife Refuge, home of the James River Ecology School…and dodder!