A World of Opportunists: The Parasitic Plants by Sydne Record One of the rarest wild plants in Massachusetts belongs to a group that must tap into the roots of nearby host plants in order to survive. Research reveals that the health of the parasite depends on the origins and life forms of the host species that are available. When we hear the word ‘parasite,’ our sucks food and water up through the minds conjure up images of animals feed- handle from the host to the parasite. ing on our own flesh. We might think of Parasitic plant species vary in the de- the recent bedbug outbreak in New York gree to which they depend upon their City or of the ticks that we hope do not host plants. Holoparasitic plants rely latch onto us as we stroll through the completely on their host plants for ob- woods. Perhaps less likely to come to taining carbohydrates because they are mind is a whole other world of equally unable to convert water, nutrients, and interesting and important opportunists, sunlight into sugars by performing photo- the parasitic plants. With nearly 4,500 synthesis. This inability to photosynthe- species spread across the globe, parasitic size is apparent in the coloration of the plants are one of the largest and most stems and leaves of holoparasites, which widespread groups of plants. Though lack chlorophyll. Dodder, for instance, is unfamiliar to many, there is an entire also known as “love vine,” because it is taxonomic family devoted to parasitic often bright red-orange and wraps itself plants: Orobanchaceae. tightly around its hosts. Unlike bedbugs and ticks, whose nour- Hemiparasitic plants are green and ishment comes from mammals, the nu- capable of performing photosynthesis, merous parasitic plants acquire mineral but they require additional water, mineral nutrients, sugar, and water by sucking nutrients, or sugars from their host plant on the roots or stems of other plants. All to reach reproductive maturity. Both ho- plants have an intricate series of pipes loparasites and hemiparasites may also called the xylem and phloem that distrib- vary in their reliance on any particular ute water and food, respectively, from one host species. Specialist parasitic plants part of the plant to another. These tissues only form haustoria with a single host mirror the plumbing system in a house species, whereas generalist parasitic that brings water from the well to the plants have a mixed diet comprised of tap. To steal resources from their hosts, resources acquired from connections to parasitic plants form haustoria – special several different species of hosts. disc-shaped structures that resemble the round rubber end of a toilet plunger (see The curious relationships between photo on facing page). The haustorium parasitic plants and their hosts pique grows into and engulfs the stem or root the interest of Congress, farmers, and of the host plant, then creates a direct conservation agencies across the world connection between the pipes of the for various reasons. For instance, Witch parasite and those of the host. Weeds (Striga species) parasitize several important crop species such as corn, sug- Once this connection is made between arcane, and sorghum. In the mid-1950s, the plumbing systems of the two plants, the United States Congress budgeted the haustoria, operating much like toilet funds for the Department of Agriculture plungers, generate a uni-directional flow. to study the infestation of Witch Weeds, Instead of pushing nutrients down the which led to a nationwide eradication drain, however, the haustorial plunger effort that significantly reduced the  Photo © Noah Charney Parasitic plants suck on their host plants’ roots with disc-shaped structures called haustoria. This picture depicts Swamp Lousewort haustoria attached to the roots of Common Rush. hemiparasite’s impact on American crop coastal beaches to alpine meadows. production. Unfortunately, in Africa, Many parasitic plants in New England are where subsistence farmers cannot af- considered rare by federal and/or state ford Witch Weed control methods, these agencies. Furbish’s Lousewort, Pedicu- plants continue to ravage harvests. In laris furbishiae, a federally Endangered contrast to the ubiquitous Witch Weeds, hemiparasite that grows only on the other parasitic plants are extremely rare. border of the United States and Canada For instance, Corpse Flower (Rafflesia along the banks of the St. John River in arnoldii R. Br.) is an elusive species that Maine, is perhaps the most famous para- grows in the jungles of Borneo. With no sitic plant found in the northeast. leaves or stems, Corpse Flower is only The story of Furbish’s Lousewort is detectable for the short time when its best told by Roy Gardner, a youthful gigantic, three-foot-diameter flowers white-haired man who has lived on the emerge. (The plant, which relies on flies shores of the St. John River for most of for pollination, was so named because the 20th and all of the 21st centuries. A it produces the fly-attracting aroma of couple of summers ago, my husband and rotting flesh.)Sustaining these species’ I had the opportunity to visit Roy while populations and the host plants that researching the louseworts. Listening to they rely upon is a primary objective of Roy as we sat watching the sun set over parasitic plant conservationists. the river on the front porch of the house he grew up in was like taking a trip in a Rare Parasitic Plants time machine. in New England He recalled his mother selling loaves of bread for a nickel along the street during New England is home to several spe- the Great Depression, the subsequent cies of parasitic plants that span a di- paving of the road, and Franklin Roos- versity of habitats ranging from sandy  One of the rarest parasitic plants in the United States, Furbish’s Lousewort, perhaps the most famous parasitic plant found in the northeast, grows along the St. John River in Maine. Photo © Noah Charney evelt’s New Deal that eventually landed dam came to a standstill and was quite him a job working on various hydroelec- controversial given the then relatively tric projects around the country. In the recent passage of the Endangered Spe- mid-1970s, there was an opportunity for cies Act. Today, Furbish’s Lousewort Roy to work on a proposed hydroelectric remains one of the rarest parasitic plants project just upstream from his home. in the United States. Simultaneously, a botanist working on One of the rarest plants in Massachu- an environmental impact assessment for setts is also a hemiparasitic species of the proposed dam, Dr. Richards, rented a the same genus as Furbish’s Lousewort: riverside cabin on Roy’s property. Swamp Lousewort (P. lanceolata). Swamp At the time, Furbish’s Lousewort had Lousewort is a late-blooming plant that not been seen for years along the St. John grows in open sunny areas that experi- and was deemed extinct, but while Dr. ence flooding in the late fall through Richards was looking out across the river early spring. The documented range of from his cabin porch he rediscovered Swamp Lousewort spans from Massachu- the rare plant. The Gardners embraced setts to Georgia on the east coast of the the presence of the rare species. They United States, and west to Missouri and housed the many researchers who came Manitoba, Canada. The species is listed to study the plants in their riverside as rare by most states along the eastern cabins and set up a sign that proudly seaboard, but it is considered common proclaimed, “Home of Furbish’s Louse- by many states in the Midwest. Historic wort.” The construction of the proposed records indicate that Swamp Lousewort  used to be more common in Massachu- An Academic-Agency setts, with several populations scattered across the state. Yet today, there is only Partnership for one extant population. Although there Swamp Lousewort is no evidence to determine precisely In 1991, the New England Wildflower how these populations became extinct, Society (NEWFS) founded the New given their documented localities, many England Plant Conservation Program of them were likely lost as a result of (NEPCoP), a group of over 65 organiza- habitat destruction due to development. tions, to prevent the extinction of the For instance, the site of one historical region’s Endangered plants. Together, population now lies beneath the waves NEWFS and NEPCoP coordinated the of the Quabbin Reservoir, which supplies production of non-regulatory conserva- drinking water for the city of Boston. tion and research plans for New England’s Currently, the management of the single Endangered flora written and reviewed by population of Swamp Lousewort in Mas- academics and conservation profession- sachusetts by the DFW’s Natural Heritage als. By proposing interesting research and Endangered Species Program relies questions relevant to the region’s rare upon understanding what the major plants, these plans encouraged collabora- threats are to the population so that its tions between students, professors, state extinction can be averted. Photo © Noah Charney The flowers of the Swamp Lousewort spring from spires of buds at the apex of the plant’s stems and do not open until quite late in the season. Several populations were once scattered across the state, but only one remains today.  Photo © Noah Charney A wild Swamp Lousewort in bloom. Looking at the plant, few would realize it is a parasite that cannot live without crucial root connections to a host species.  and federal agencies, and conservation forming connections with multiple host professionals. Several success stories species including Reed Canary Grass. resulted from this program where aca- We did not, however, know whether or demic-agency partnerships have formed not these non-native grasses were high around species with a conservation and quality hosts for Swamp Lousewort. research plan. As a generalist hemiparasitic species In 2001, Dr. Dorothy Allard wrote a NEP- that both photosynthesized and para- CoP conservation and research plan for sitized for resources, the value of any Swamp Lousewort that identified prob- particular host plant depended on the able threats to existing populations of degree to which the hemiparasite benefit- Swamp Lousewort in Massachusetts and ted from water and nutrients acquired Connecticut. Some of the possible threats from the host, versus the amount that the to the species mentioned by Allard includ- host plant shaded out the hemiparasite, ed deer or beetle herbivory, competition thereby preventing it from photosyn- with invasive species, shading by woody thesizing. To determine whether or not native plants, and habitat modification non-native invasive species growing near as a result of activities such as grazing, Swamp Lousewort should be removed, I mowing, or drainage of wetlands. In 2007, conducted greenhouse and field experi- the Massachusetts Natural Heritage and ments. Endangered Species Program followed up In the greenhouse, I grew Swamp Louse- on Allard’s plan by updating the state- wort with native, non-native invasive, or a specific management plan for Swamp mixture of native and non-native invasive Lousewort. To do this, the now-retired graminoids (grasses). The native grami- state botanist, Paul Somers, assembled a noids were Woolgrass (Scirpus cyperinus) team consisting of Elizabeth Farnsworth and Common Rush (Juncus effusus). The (New England Wildflower Society), Karro non-native invasive graminoids were Frost (environmental consultant), and Reed Canary Grass and Smooth Brome. myself (University of Massachusetts I also clipped the host plants in half of Amherst graduate student). the pots evenly distributed across the As we reviewed all of the existing different combinations of hosts to see information about Massachusetts’ sole how a clipping management treatment population of Swamp Lousewort, it was would affect the hemiparasites. evident that there were several unan- Swamp Lousewort grew significantly swered questions about the biology of the larger, produced more flowers, and had plant that, if answered, would help us to higher survival rates when grown with develop the best management practices native host plants compared to when it for the species. These questions became was grown with non-native invasive host the focus of my doctoral dissertation plants in monocultures or in mixtures research. For instance, the Massachu- with natives. Further, clipping the host setts population of Swamp Lousewort plants, regardless of whether they were occurred at a site where there were also natives or non-native invasives, nega- several non-native invasive species. In tively impacted the size and flowering particular, Reed Canary Grass (Phalaris of Swamp Lousewort. This evidence arundinacea) and Smooth Brome (Bromus suggested that the removal of Reed inermis), plants brought over from Asia Canary Grass and Smooth Brome from to provide fodder for livestock, grew in around the Massachusetts population abundance. was warranted, but that the removal Removing highly competitive, non-na- method should not also harm nearby tive invasive species growing with rare native host plants. native plants is a common management The greenhouse experiment was useful practice, but given the hemiparasitic in that it provided a controlled setting nature of Swamp Lousewort, eradicat- for exploring host-hemiparasite relation- ing such species could potentially have ships, but Swamp Lousewort growing taken out important host plants. From wild outdoors experiences multiple other previous studies by other researchers, stressors, such as fluctuations in weather, we knew that as a generalist hemipara- that also required investigation. The next site, Swamp Lousewort was capable of step after the greenhouse experiment  was to see how native versus non-native effect of beaver activity on the plants. invasive plants performed as host plants The population of Swamp Lousewort at the site of the Massachusetts popula- in Massachusetts grew in several tion of Swamp Lousewort. patches along a small stream that was In the field, I tagged several hundred also home to beavers. When we wrote Swamp Lousewort individuals in invaded the state management plan there was and uninvaded patches, and measured the tagged plants’ survival, growth, and reproduction for 3 consecutive years. I was then able to use this data in a mathematical model to see how the growth rates of the invaded portion of the population differed from the uninvaded por- tion of the population. During the first half of the study, Swamp Lousewort growing in uninvaded patches had higher popu- lation growth rates than plants growing in invaded patches. However, in the second half of the study, the population growth rates of Swamp Lousewort growing in the uninvaded patches were lower than plants in the invaded patches. Over the course of the 3- year study, native woody shrubs called alders (Alnus species) grew and began to cast heavy shade onto the Swamp Lousewort. Many management plans emphasize the removal of non-native invasive plants growing around native rare plants, but this field study stressed the importance of consider- ing the growth forms of co-occurring species, in addition to their origins. In this case, the natural One of the focus areas of the author’s research was growth of native species determining if Swamp Lousewort would grow better (alders) appeared to have with invasive, non-native species, or with native hosts. a direct, negative effect on In the controlled environment of a greenhouse, she a rare native species. demonstrated that Swamp Lousewort grew larger, Another potential threat had better survival, and produced more flowers when to Swamp Lousewort that growing with native as opposed to non-native invasive we identified in the state host grasses. Above, growing with the non-native grass management plan was the Smooth Brome, and right, with our native Woolgrass. 10 no prior information on the effects of had a negative effect on the population beaver flooding on the hemiparasites. size of Swamp Lousewort during the In addition to tagging and measuring study, beaver also played an important plants in uninvaded and invaded areas long-term role in maintaining the open, for 3 years, I also followed the fates of sunny habitat needed by the hemipara- individuals in all of the patches along sites. As such, management activities the stream. directed at conserving the plants needed In year one of the study, flooding caused to acknowledge this tenuous dynamic by beaver dams nearly wiped out two in which beaver act as both creators of the patches of Swamp Lousewort. and destroyers of Swamp Lousewort’s Simulating the potential fate of Swamp habitat. Lousewort based on these data showed The results of this research are now that the frequency of beaver flooding had being used by the Massachusetts Natu- a strong influence on the population’s risk ral Heritage and Endangered Species of extinction. Although beaver flooding Program to inform the best management Photos © Noah Charney practices for Swamp Lousewort. As a graduate student, I found that the academic-agency part- nership formed to answer the questions needed for the man- agement of Swamp Lousewort led to a number of invaluable re- sources. Because of the “directly applied” aspect of my work, the project was more competitive for grants from a variety of sources, including funds from the university, state programs, and the private sector. Also, I developed contacts with people who had diverse perspectives on topics ranging from theoretical to practical issues, which en- riched the context of the stud- ies. One purpose of the NEWFS and NEPCoP conservation and research plans was to bridge the academic-agency divide, and they fulfill this goal. There are many intriguing plants with conservation and research plans that are still in need of study. Spread the word – the opportuni- ties are out there!

Sydne Record is a postdoctoral research fellow at the Harvard For- est Long Term Ecological Research Site in Petersham, Massachusetts. She would like to thank NC for his help in editing this article.

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