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!
In the 40 years since the Clean Water Act was passed, we have
made great strides toward fishable and swimmable waters. The James is arguably
one of the rivers that has been the most improved – coming back from a 13-year
fishing ban to recently being lauded as the river that runs through Outside Magazine’s Best
River Town.
