T Nuhfer | December 11, 2024

If you spend much time in Eastern deciduous forests, you’ve probably encountered several notorious local parasites. Chances are you’ve been bitten by mosquitos, ticks, or even leeches. But unless you’ve been looking very closely, you might not have noticed some of these forests’ most interesting parasites hiding in plain sight.

Epifagus virginiana (Fig.1a) , also called beech drops, is a small flower that exclusively parasitizes American beech trees (Fagus grandifolia) (Fig. 1b)

Figure 1a (left) – Beech drops (E. virginiana). (Source: Gilles Ayotte via Wikimedia Commons)

Figure 1b (right) – American beech (F. grandifolia) (Source: Katja Schulz via Wikimedia Commons)

 E. virginiana is the only species in its genus. Most plants, including beech trees, get their energy from photosynthesis, where solar energy triggers a chemical reaction in the chloroplasts inside their cells. This process also gives beech leaves their green color. But while beech trees drink up the sun, beech drops take their sugars straight out of their host trees. Beech drops and other parasitic plants have a special organ that pierces the tissues of the host plant and diverts or absorbs resources, called a haustorium. 

The word “symbiosis” is often used to describe a mutually beneficial ecological interaction (also called mutualism), but parasitism is also a type of symbiosis. Symbiosis literally translated means “living together”. Parasitism represents a finely-honed and intimate ecological relationship between parasite and host, where the parasite benefits and the host does not. 

Beech drops aren’t the only plants using this clever resource-acquisition strategy – dodders, ghost pipes, and mistletoes also parasitize. Parasitism in plants has evolved independently at least 12 times [1]. While some parasitic plants engage in both photosynthesis and parasitism (also known as hemiparasitism), beech drops don’t photosynthesize at all. For that reason, these little plants have no chlorophyll – the stems and flowers are striped cream and purplish brown, and they have only tiny, vestigial leaves (Fig. 2). From a distance, they look like dried twigs or sticks. Because these flowers die in the winter, they can’t continue to grow and feed from the same host year after year. For that reason, they don’t seem to do any significant damage to their hosts. In fascinating and rare cases, beech drops have been observed in autoparastic relationships, ‘feeding’ from other members of their own species (Fig. 3) [2].

Figure 2 – Flowers of E. virginiana. (Source: Douglas Goldman via Wikimedia Commons)

Figure 3 – Herbarium specimen of E. virginiana engaged in autoparasitism, rooted in another member of the same species instead of a beech tree. (Source: Teixeira-Costa, 2024).

These plants are very poorly understood. Only two papers about the species were published in the last year. Beech drops mostly self-pollinate, and though they make a few flowers which may cross-pollinate, those cross-pollinating flowers are mostly sterile [3]. Little is recorded about the pollination ecology of beech drops, though in 2013, researchers in North Carolina found ants visiting beech drops and carrying pollen [4]. If there are animals that eat the seeds or browse the plants, those interactions are undocumented – and may be entirely unknown. In the last few years, scientists have begun to document the microbiomes of beech drops in an attempt to better understand how the haustorium functions [5].

For scientists, beech drops are an interesting lens into evolutionary processes because of how parasitism has allowed them to evolve away from photosynthesis [6]. Because beech drops are sensitive to disturbance and prefer old, dense beech stands, they’ve been used as indicators to assess forest community health [7]. But another parasite is putting beech drops at risk. 

Litylenchus crenatae mccannii is a parasitic nematode responsible for Beech Leaf Disease [8] (Fig 4). This new disease rapidly spreads and kills young beech trees at high rates [9]. This will lead to a massive shift in Eastern deciduous forests in the United States, where beech trees are foundational species [9]. Since beech drops depend on the health of their beech tree hosts, these mysterious flowers may begin to disappear. 

Figure 4a (left) – Beech leaf disease caused by L. crenatae mccannii. You can report sightings of Beech Leaf Disease in Massachusetts at this link. Many other states have similar reporting programs. Source: Sandy Wolkenberg via Wikimedia Commons

Figure 4b (right) – Microscope images of  L. crenatae mccannii. (Source: Carta et al., 2020)

The words host and guest both come from the proto-Indo-European root word ghos-ti [10]. Ghos-ti meant guest and host, since it was assumed that hospitality was always broadly reciprocal. Beech trees host beech drops, and beech drops host their own secret ecosystems of microbiota and symbionts. As I’ve learned more about mycorrhizae, soil microbes, and the human microbiome, the term ghost-ti has increasingly influenced my understanding of ecological interdependence. Beech drops, like the rest of us, take their turns as guests and hosts.

And beech drops, amazing little flowers that they are, have intrinsic value. They can remind us of the multitudes of unseen organisms living in strange, fascinating ways all around us. For every beech tree that is lost in this biodiversity crisis, we may lose many more living beings, and we lose the chance to understand them. But it isn’t too late to get to know beech drops better. The other early meaning of the word ghos-ti was stranger. Who is a stranger but someone you haven’t met yet? Want to study beech drops? Please – be my guest!

References 

[1] Westwood, James H., John I. Yoder, Michael P. Timko, and Claude W. dePamphilis. “The Evolution of Parasitism in Plants.” Trends in Plant Science 15, no. 4 (April 1, 2010): 227–35. https://doi.org/10.1016/j.tplants.2010.01.004.

[2] Teixeira-Costa, Luiza. “Cannibal Plants: Intraspecific Autoparasitism among Host-Specific Holoparasites.” Botany 102, no. 3 (March 2024): 176–83. https://doi.org/10.1139/cjb-2023-0081.

[3] Thieret, John W. “Notes on Epifagus.” Castanea 34, no. 4 (1969): 397–402.

[4] Abbate, Anthony P., and Joshua W. Campbell. “Parasitic Beechdrops (Epifagus Virginiana): A Possible Ant-Pollinated Plant.” Southeastern Naturalist 12, no. 3 (September 2013): 661–65. https://doi.org/10.1656/058.012.0318.

[5] Lafferty, Jasmine, Aida Jimenez Esquilin, and Desiree Evans. “Microbiome Associated with the Haustorium of Epifagus Virginiana.” Proceedings of the West Virginia Academy of Science 93, no. 1 (April 1, 2021). https://doi.org/10.55632/pwvas.v93i1.804.

[6] Hida, Shintaro, Marie Nishio, Kazuma Uesaka, Mari Banba, Nobuyuki Takatani, Shinichi Takaichi, Haruki Yamamoto, Kunio Ihara, and Yuichi Fujita. “Microevolution toward Loss of Photosynthesis: Mutations Promoting Dark-Heterotrophic Growth and Suppressing Photosynthetic Growth in Cyanobacteria.” bioRxiv, April 12, 2024. https://doi.org/10.1101/2024.04.08.588626.

[7] Wesche, Spencer L., Elizabeth L. Barker, and Alice L. Heikens. “Population Ecology Study of Epifagus Virginiana (L.) W.P.C. Barton (Beechdrops) in Central Indiana.” Proceedings of the Indiana Academy of Science 125, no. 1 (2016): 69–74.

[8] Carta, Lynn Kay, Zafar A. Handoo, Shiguang Li, Mihail Kantor, Gary Bauchan, David McCann, Colette K. Gabriel, et al. “Beech Leaf Disease Symptoms Caused by Newly Recognized Nematode Subspecies Litylenchus Crenatae Mccannii (Anguinata) Described from Fagus Grandifolia in North America.” Forest Pathology 50, no. 2 (2020): e12580. https://doi.org/10.1111/efp.12580.

[9] Ewing, Carrie J., Constance E. Hausman, John Pogacnik, Jason Slot, and Pierluigi Bonello. “Beech Leaf Disease: An Emerging Forest Epidemic.” Forest Pathology 49, no. 2 (2019): e12488. https://doi.org/10.1111/efp.12488.

[10] Watkins, Calvert. The American Heritage Dictionary of Indo-European Roots. Houghton Mifflin Harcourt, 2000.