The trails at East Point Sanctuary in Biddeford Pool are a spectacular place to walk on a late summer afternoon. While it’s difficult to look away from the panoramic ocean views or abundant sea life, if you look carefully along the trailside, you can see some of Maine’s parasitic plant species.
There are many parasitic plants in Maine, but they often go undetected because their parasitism is not quite as obvious as animal parasites, like ticks or lice. Most parasitic plants attach to other plants or fungi, and draw some or all of their nutrients from their host; generally, this harms the host species without killing it. In fact, many parasitic species are signs of a healthy, diverse ecosystem, and can help to moderate aggressive species while allowing other species to flourish. You can contrast this with the effects of invasive species, which often overgrow and kill other plants around them, leading to less diverse ecosystems.
The most well-known parasitic plants are probably Ghostpipes (Monotropa uniflora); their ghostly white appearance is due to a lack of chlorophyll, the green pigment responsible for photosynthesis. These members of the Ericaceae (Blueberry family) are usually found in the forest understory, where they attach to mycorrhizal fungi (mostly in the genus Russula), which are themselves attached to tree roots in a symbiotic relationship. They draw nutrients directly from the fungi, and indirectly from the plants.
The species of parasitic plants at East Point Sanctuary are more typical of open habitats, and also more directly parasitic on other plants. Dodders are a common group of parasitic plants found worldwide; at East Point, you can see Common Dodder (Cuscuta gronovii).
This vining species is easy to spot from its golden, stringy appearance, like a handful of string tossed on top of other plants. You have to look very closely to see the tiny, scale-like leaves, which is a common feature of fully parasitic species, in addition to white or yellowish coloration. Like Ghostpipes, this species belongs to a family (Convolvulaceae) with many nonparasitic species, including morning glories and sweet potatoes.
When Common Dodder starts growing, it has a small root and can photosynthesize at very low levels, but as soon as it can, it attaches to a host plant and inserts haustoria into the plant’s vascular system. These haustoria are the structures that most parasitic plants use to take nutrients from their hosts. Dodders will continue to vine over other plants as long as the growing season allows, and are capable of attaching to many different host species, including the Poison Ivy in the photo.
An even less obvious group of parasites are the false foxgloves in the genus Agalinis. Pictured above, Purple False Foxglove (Agalinis purpurea) is the most common representative of this group found at East Point. You can see that this looks mostly like a normal plant, with green foliage indicating its ability to photosynthesize. Purple False Foxgloves, and most of its relatives in the Orobanchaceae (Paintbrush family), are hemiparasites that both photosynthesize and produce haustoria that attach to the root system of host plants. Earlier in the summer, you can see other members of this family, like Narrowleaf Cow-wheat (Melampyrum lineare) and Yellow Rattle (Rhinanthus minor).
While it may seem like cheating, parasitic species are almost always adapted to environments with low nutrients and/or high disturbance. It is not hard to see both of these factors at play at East Point, with sand and rock underfoot and constant wind and salt spray. Keep an eye out for these fascinating plant species on your next walk around the sanctuary!
