Beechdrops (Epifagus virginiana) are annual flowering plants which parasitize beech tree roots all over Eastern North America. They completely lack chlorophyll and have smooth, brownish stems and branches that reach a height of about 30cm (Musselman, 1982). During our own observations, they were very easy to miss under all the autumn leaf litter, because they blended in so well.
In late summer and early fall, beechdrops produce two types of flowers called cleistogamous and chasmogamous flowers. Cleistogamous flowers are produced first, on the lower part of the stem. These fertile flowers remain closed and self-fertilize.
Chasmogamous flowers, on the other hand, are produced only occasionally. They grow higher on the stem and are fully open. They bear petals fused into a bell-shaped structure and possess a bright yellow functional nectary to attract pollinators (Musselman, 1982; Thieret, 1969). We actually found a few beechdrops with these flowers and we were able to observe the small but vivid nectary.
Chasmogamous flowers are mostly considered sterile, but there have been reports of them bearing fruit, possibly with the help of ant pollinators (Abbate & Campbell, 2013).
Relationship with Beech Trees
Beechdrops depend on their host species, the American Beech tree (Fagus grandifolia) for survival. The parasite attaches itself with a structure called a haustorium, which is the part of the plant’s root that penetrates the tissue of the tree (Musselman, 1982).
Through this process, beechdrops are able to obtain water and food from beech tree roots. As they mature, new roots called ‘grapplers’ form, which stabilize the plant in the leaf litter (Musselman, 1982). Since beechdrops are annual plants, their parasitic effect on beech trees is minimal and the relationship is not considered detrimental to the host.
Beechdrops can occur anywhere beech trees grow, because they adapt to a wide range of habitats (Grafton, 2008). However, Tsai and Manos (2010) demonstrated that when the range of the beech tree changes, the parasite’s range does not. Instead, beechdrops depend more on tree density. Since we only sampled the Morgan Arboretum, we couldn’t compare the densities of different forests. However, we did notice that certain areas within the forest that contained a higher amount of beech trees subsequently had more beechdrops.
Beech Bark Disease
Beech Bark Disease (BBD) is an infection comprised of two parts; the scale insect Cryptoccocus fagisuga and one of two fungi from the genus Nectria (Morin et al., 2007). The infection starts with beech scale insects that weaken the bark by inserting their tubular stylets into the beech tree to feed (Houston & O’brien, 1983). A stylet is the part of the insect’s mouth that penetrates the tissue of whatever it is feeding on, in this case tree bark. This renders the bark susceptible to invasion from either N. coccinea or the N. galligena (Houston & O’brien, 1983). There were many trees in the Morgan Arboretum infected with BBD. The symptoms we observed were large holes, soft bark as well as some of the red spores from the fungus during its reproductive stage.
The fungi spores which look like red hollow circles
BBD first appeared in Europe around 1849 then crossed over to North America in the 1890s (Houston & O’brien, 1983). The first sightings were in Halifax and it has been spreading outward ever since. Morin et al. (2007) estimate the disease spreads approximately 14.7 km/year and that BBD reached the Saint-Lawrence lowlands between 1960 and 1975.
We thought it would be interesting to recognize any factors that might contribute to beechdrop growth. Since their survival is dependent on the host tree, we wanted to understand whether the size or the health of the beech tree affected the height of the beechdrops. We also wanted to discover if the distance from the host tree influenced the beechdrops in any way. In the end our question became: Is there any correlation with the health and/or size of a beech tree, as well as the distance from the tree, all versus the size of the beechdrop?
To carry out our experiment, we sampled a total of 20 trees in four separate sections of the Morgan arboretum. We preferred solitary beech trees in order to make sure it was the only host tree supplying nutrients to the surrounding beechdrops. Otherwise, our samples were completely random. We measured the height of each beechdrop around the tree, as well as their distance, up to a maximum of 15 randomly selected beechdrops. In addition, we measured the diameter of each tree at breast height (DBH).
A demonstration of how we measured the DBH of each tree:
A tutorial showing how we measured the distance and height of each beechdrop:
Lastly, we came up with a scale in order to rank how healthy each beech tree was, 1 being the healthiest and 5 being the most diseased and dying beech trees.
Despite obtaining a large amount of data, there was no significant correlation between the health of the beech tree and the size of the beechdrop. Additionally, we did not find any correlation between the size of the tree and the size of the beechdrop nor the distance from the tree and the size of the beechdrop. However we did notice that many beechdrops preferred to grow near disturbed trails.
This entire experience of gathering data in the autumnal forest was a pleasure. Though we may not have found any significant correlations, we hope that another group will take up the challenge next year.
Abbate, A. P., & Campbell, J. W. (2013). Parasitic Beechdrops (Epifagus virginiana): A Possible Ant-Pollinated Plant. Southeastern Naturalist, 12(3), 661-665.
Grafton, Emily. “Beechdrops.” Mountain State Flora. 2008. Web. 27 Sept. 2015. <http://www.wvdnr.gov/wildlife/magazine/archive/08fall/Vol8No2msfBeechdrops.pdf>.
Houston, D. R., & O’brien, J. T. (1983). Beech Bark Disease. Retrieved from Invasive and exotic species of North America: http://www.invasive.org/symposium/houston.html
Morin, R. S., Liebhold, A. M., Tobin, P. C., Gottschalk, K. W., & Luzader, E. (2007,
June 9). The spread of beech bark disease in the eastern United States and its relationship to regional forest composition. Canadian Journal of Forestry Research(37), 726-736. doi:10.1139/X06-281
Musselman, L. J. (1982). The Orobanchaceae of Virginia. Castanea, 47(3), 266-275.
Thieret, J. W. (1969). Notes on Epifagus. Castanea, 34(4), 397-402.
Tsai, Y., & Manos, P. (2010). Host density drives the postglacial migration of the tree parasite, Epifagus virginiana. Proceedings of the National Academy of Sciences, 107(39), 17035-17040. doi:10.1073/pnas.1006225107.