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Population ecology study of Epifagus Virginiana (L.) W.P.C. Barton (Beechdrops) in Central Indiana.

INTRODUCTION

Epifagus virginiana (L.) W.P.C. Barton is a holoparasitic plant that lacks chlorophyll (Porcher & Rayner 2001; Tsai & Manos 2010; Weakley et al. 2012; Yatskievych 2013) and is an obligate parasite interacting solely with the roots of Fagus grandifolia Ehrh. (Deam 1940; Brooks 1960; Gleason & Cronquist 1991; Yatskievych 2000; Mohlenbrock 2002; Jones 2005; Rhoads & Block 2007; Tsai & Manos 2010; Homoya2012; Abbate & Campbell 2013). These plants grow in mesic, eastern deciduous forests, occupying the same range as their host (Thieret 1969; Smith 1994; Chapman et al. 1998, 2008; Yatskievych 2000; Porcher & Rayner 2001; Tsai & Manos 2010; Homoya 2012; Abbate & Campbell 2013). Both plants have a coefficient of conservatism of 8, indicating they grow in high-quality plant communities and tolerate little disturbance (Rothrock 2004).

Epifagus virginiana is a member of the Orobanchaceae or Broomrape family. Traditionally, species in this family were non-green, root parasites that relied entirely on deciduous host trees. These herbaceous plants were characterized by having small, scale-like leaves, irregular flowers, and fruit capsules that produced an abundance of small seeds (Radford et al. 1968; Jones 2005). However, today, Orobanchaceae also includes hemiparasitic species and is comprised of 89 genera and 2061 species (Bennett & Mathews 2006). These species are distributed worldwide, but are most predominant throughout the Mediterranean, Southern Africa, the Himalayas, and North America (Bennett & Mathews 2006).

Most botanists describe Epifagus virginiana as an annual (Thieret 1969; Yatskievych 2013; Porcher & Rayner 2001; Tsai & Manos 2010; Abbate & Campbell 2013); however, they have also been reported as a perennial (Homoya 2012; Weakley et al. 2012). These non-showy, brown, twig-like plants are 10-15 cm tall (Yatskievych 2000; Homoya 2012) with branches bearing alternate scale-like leaves and two types of flowers (Homoya 2012) (Fig. 1). Epifagus flowers from August to October (Gleason & Cronquist 1991; Chapman et al. 1998, 2008; Mohlenbrock 2002; Jones 2005; Homoya 2012; Yatskievych 2013); however, the dried plant stalks persist throughout winter (Porcher & Rayner 2001).

The open, chasmogamous flowers (1 cm) of Epifagus are tubular, having four purple and white petals and are located on the upper portion of the stem (Radford et al. 1968; Homoya 2012; Abbate & Campbell 2013) (Fig. 2). These flowers are considered to be sterile (Radford et al. 1968; Gleason & Cronquist 1991; Porcher & Rayner 2001; Homoya 2012; Weakley et al. 2012; Yatskievych 2013). Occasionally, however, long-tongued bees and ants have been observed visiting them, possibly attracted to a nectary found near the ovary of the chasmogamous flower. Infrequently, these flowers produce fruits and seeds (Abbate & Campbell 2013). Normally, chasmogamous flowers are few in comparison to the self-fertile, closed cleistogamous flowers.

Cleistogamous, closed, spike-like flowers (4-6 mm) are found near the base of the plant and produce seeds (Radford et al. 1968; Jones 2005; Homoya 2012; Yatskievych 2013) (Fig. 3). The small, dust-like seeds are washed deep into the soil, in close proximity to F. grandifolia roots (Porcher & Rayner 2001; Jones 2005). These roots release a chemical, signaling the seeds to germinate in spring (Porcher & Rayner 2001; Jones 2005; Grafton 2008).

Epifagus virginiana, which is found throughout southern Indiana counties (Fig. 4), is scattered throughout northern Indiana (Deam 1940; Yatskievych 2000) with a recent new record for Johnson County (specimen #155310 housed in Friesner Herbarium (BUT) at Butler University). As high quality forests are degraded by habitat fragmentation, invasive species, and anthropogenic disturbances, the high quality sites where F. grandifolia and E. virginiana occur are at high risk for declining populations. There is also a lack of information about this relatively inconspicuous species and its population ecology. The objectives of this research are to establish baseline information about the size and locations of E. virginiana within Hougham Woods Biological Field Station (HWBFS) in Johnson County, Indiana, to determine the size and morphological characteristics of these plants, to examine the reproductive potential of the Epifagus population, and to examine host tree size and location.

METHODS

Study site.--HWBFS is a 12 ha relatively flat, mesic forest that was donated to Franklin College in 2006. Dominant canopy species include Acer saccharum Marshall, F. grandifolia, and Quercus spp. (Smith & Heikens 2014). The forest is located in Johnson County east of Franklin, Indiana in the Tipton Till Plain Section of the Central Till Plain Natural Region (Fig. 4). In this region, soil types are often neutral silt and silty clay loams (Homoya et al. 1985; Smith & Heikens 2014). HWBFS is surrounded by agricultural field and an industrial park, and has experienced disturbances, including selective cutting and wind throw (Smith & Heikens 2014). Despite these disturbances, a few species with high coefficients of conservatism, such as F. grandifolia and Aplectrum hyemale (Muhl. ex Willd.) Torr., persist in the forest.

From September to November 2013, E. virginiana and their associated host trees were located, flagged, and numbered in HWBFS and marked using GPS. The locations were mapped using ArcGIS software. To establish baseline data on the size of Epifagus plants, large populations ([less than or equal to] 40 plants) were randomly sampled (all plant numbers ending in 2) and measured for the following morphological characteristics: plant height (cm), number of branches, number of chasmogamous and cleistogamous flowers, and distance (cm) to nearest host tree. In small populations (< 40 plants), this data was gathered for all plants. In total, 225 plants were examined.

Twenty plants from the entire population were randomly selected for seed production. The 10th capsule from the bottom of the plant was examined if the capsule was intact. The capsules were weighed, then opened and the seeds were weighed and counted.

To investigate chasmogamous flowers, in the largest population (470 plants), 32 plants were randomly selected and examined for chasmogamous and cleistogamous flower ratios. In addition, 50 plants were randomly selected from the three largest populations to determine if seeds were produced in chasmogamous flowers. Plants taller than 25 cm were examined because chasmogamous flowers were not found on plants shorter than 16 cm.

In the summer of 2014, all Fagus trees in HWBFS were flagged and marked using GPS. The trees were grouped into the following DBH (cm) size classes arbitrarily: 0-10, 11-20, 21-30, 31-40, 40+ cm. Host trees were examined for number of Epifagus plants, average height (cm), and average distance to host trunk (cm). Epifagus plants were assumed to parasitize the nearest Fagus tree. Minitab 17 was used for the Pearson Correlations.

RESULTS AND DISCUSSION

In 2013, 886 Epifagus plants were found growing on 17 host trees in the interior of HWBFS. The 225 Epifagus plants that were measured in HWBFS were larger (16.1 cm) than the size documented in Indiana (10-15 cm) (Yatskievych 2000) (Table 1); however, the observed heights were similar to ranges reported throughout the Midwest (15-60 cm) (Chapman et al. 1998, 2008; Porcher & Rayner 2001; Homoya 2012; Weakley et al. 2012). Distances between Epifagus and their host trunks varied widely (Table 1). Large variations were also discovered when examining the morphological characteristics of the plants, i.e., number of branches and number of flowers (Table 1). Plants had multi-branched stems averaging 6 stems and 61 flowers per plant. Flower totals varied from 3 to 471 per plant (Table 1).

Epifagus is reported as producing an abundance of small seeds (Radford et al. 1968; Jones 2005; Homoya 2012; Yatskievych 2013) and the results from this study are consistent with this (Table 1). In 2013, 20 cleistogamous flowers from 20 different plants produced approximately 16,500 seeds with an average weight of 7.38 [micro]g per seed (Table 1). The large number of seeds per cleistogamous capsule, combined with the high cleistogamous flower presence per plant (Table 2), suggests that the overall Epifagus population in HWBFS has a high reproductive potential. Chasmogamous flowers occurred in much smaller numbers per plant and were limited to larger plants (Table 2). While these flowers have been reported as being pollinated and producing seeds (Abbate & Campbell 2013), this study supports the more common findings that these flowers are sterile (Radford et al. 1968; Gleason & Cronquist 1991; Porcher & Rayner 2001; Homoya 2012; Weakley et al. 2012; Yatskievych 2013). In an examination of 50 chasmogamous flowers from large Epifagus (average height 29.4 cm), no seeds were discovered. The ratio of cleistogamous to chasmogamous flowers in this study was 20:1.

In 2014, 415 Fagus trees were located throughout HWBFS, 17 of which were associated with Epifagus populations (Table 3). The majority of Epifagus were associated with trees in the 40+ DBH size classes and none were found in the smallest size class of 0-10.9 cm (Table 3). Also, the largest Epifagus populations were supported by trees that had a DBH of 40+ cm. However, there was not a significant (p [less than or equal to] 0.05) correlation between tree size and size of the Epifagus population ([R.sup.2] = 0.47, p = 0.053). This lack of a significant correlation may be due to the shortest Epifagus plants being associated with trees that were 33.7 and 48.4 cm DBH, respectively. It appears that factors other than tree size impact Epifagus growth. There was also a lack of a significant correlation between mean height of Epifagus and tree size ([R.sup.2] = 0.18, p = 0.47), or tree size and distance of Epifagus from the host trunk ([R.sup.2] = 0.10, p = 0.71). It is possible that large Fagus trees produce an abundance of chemicals that trigger Epifagus germination (Porcher & Rayner 2001; Jones 2005; Grafton 2008). It is unknown if younger trees are more resistant to E. virginiana, if it takes a number of years for above ground stems to form, or what environmental factors impact germination.

In conclusion, the large population of E. virginiana at HWBFS has a high reproductive potential due to its abundance of plants, number of flowering plants, and number of seeds per capsule. Additional research is needed to determine the impact of chemicals released by the host species on germination and how environmental conditions impact Epifagus population sizes. The abundance of E. virginiana and F. grandifolia, is one indicator that HWBFS is a relatively high-quality forest remnant and the continued monitoring of these populations in HWBFS may be one way to determine the quality of the forest overtime.

ACKNOWLEDGMENTS

This research was funded in part by the Franklin College Endowed Undergraduate Field Biology Research Scholarship and a Franklin College Undergraduate Research Grant. The authors greatly appreciate the GIS assistance provided by Dr. Benjamin O'Neal, and the field assistance of Kenzie Glassburn and Derrek Barker is greatly appreciated.

LITERATURE CITED

Abbate, A.P. & J.W. Campbell. 2013. Parasitic beechdrops (Epifagus virginiana): a possible ant-pollinated species. Southeastern Naturalist 12:661-665.

Bennett, J.R. & S. Mathews. 2006. Phylogeny of the parasitic family Orobanchaceae inferred from phytochrome A. American Journal of Botany 93:1039-1051.

BONAP. 2014. North American plant atlas. Chapel Hill, North Carolina. At: http://www.bonap.org (Accessed 22 March 2016).

Brooks, A.E. 1960. A preliminary morphological study of Epifagus virginiana (L.) Bart. Proceedings of the Indiana Academy of Science 70:73-78.

Chapman, W.K., V.C. Chapman, A.E. Bessette & A.R. Bessette. 1998. Wildflowers of New York in Color. Syracuse University Press, Syracuse, New York. 168 pp.

Chapman, W.K., V.C. Chapman, A.E. Bessette & A.R. Bessette. 2008. Wildflowers of Massachusetts, Connecticut, and Rhode Island in Color. Syracuse University Press, Syracuse, New York. 200 pp.

Deam, C. 1940. Flora of Indiana. Department of Conservation, Wm. B. Burford Printing Co., Indianapolis, Indiana. 1236 pp.

Gleason, H.A & A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. New York Botanical Garden, Bronx, New York. 910 pp.

Grafton, E. 2008. Beechdrops. Mountain State Flora 8:19.

Homoya, M.A. 2012. Wildflowers and Ferns of Indiana Forests: A Field Guide. Indiana University Press, Bloomington, Indiana. 438 pp.

Homoya, M.A., D.B. Abrell, J.R. Aldrich & T.P. Post. 1985. The natural regions of Indiana. Proceedings of the Indiana Academy of Science 94:245-268.

Jones, R.L. 2005. Plant Life of Kentucky: An Illustrated Guide to the Vascular Flora. The University Press of Kentucky, Lexington, Kentucky. 834 pp.

Mille-Isles, C., Flickr Creative Commons. 2011. Epifagus/Beechdrops. At https://flic.kr/p/ amwZqf CC by 2.0 https://creativecommons.org/ licenses/by/2.0/legalcode (Accessed 22 March 2016).

Mohlenbrock, R.H. 2002. Vascular Flora of Illinois. Southern Illinois University Press, Carbondale, Illinois. 512 pp.

Porcher, R.D & D.A. Rayner. 2001. A Guide to the Wildflowers of South Carolina. University of the South Carolina Press, Columbia, South Carolina. 551 pp.

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Rhoads, A.F. & T.A. Block. 2007. The Plants of Pennsylvania: An Illustrated Manual. University of Pennsylvania Press, Philadelphia, Pennsylvania. 1056 pp.

Rothrock, P.E. 2004. Floristic Quality Assessment in Indiana: the Concept, Use, and Development of Coefficients of Conservatism. Final Report for ARN A305-4-53 EPA Wetland Program Development Grant CD975568-01. 96 pp.

Ruch, D.G., A. Schoultz & K.S. Badger. 1999. The flora and vegetation of Ginn Woods, Ball State University, Delaware County, Indiana. Proceedings of the Indiana Academy of Science 107:17-60.

Smith, E.B. 1994. Keys to the Flora of Arkansas. The Ozark Society Foundation, Fayetteville, Arkansas. 363 pp.

Smith, M.E. & A.L. Heikens. 2014. A two year population ecology study of puttyroot orchid (Aplectrum hyemale (Muhl. ex Willd.) Torr.) in Central Indiana. Proceedings of the Indiana Academy of Science 123:131-137.

Thieret, J.W. 1969. Notes on Epifagus. Castanea 34:397-402.

Tsai, Y.E. & P.S. Manos. 2010. Host density drives the postglacial migration of the tree parasite, Epifagus virginiana. Proceedings of the National Academy of Sciences 107:17035-17040.

Weakley, A.S., J.C. Ludwig & J.F. Townsend. 2012. Flora of Virginia. Botanical Research Institute of Texas Press, Fort Worth, Texas. 1554 pp.

Yatskievych, G. 2013. Steyermark's Flora of Missouri, Vol. 3. Missouri Botanical Garden Press. St. Louis, Missouri. 1381 pp.

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Manuscript received 22 April 2016, revised 11 July 2016.

Spencer L. Wesche, Elizabeth L. Barker and Alice L. Heikens (1): Department of Biology, Franklin College, 101 Branigin Boulevard, Franklin, IN 46131 USA

(1) Corresponding author: Alice L. Heikens, 317-738-8302 (phone), aheikens@franklincollege.edu.

Caption: Figures 1-3.--Epifagus virginiana. 1. Entire plant. 2. Chasmogamous flower. 3. Cleistogamous flower. (Photos 1 & 2 by Kay Yatskievych; photo 3 by Charles de Mille-Isles (2011).)

Caption: Figure 4.--Distribution of Epifagus virginiana in Indiana. Light shading indicates distribution from BONAP (2014), hashing indicates new records in several counties (K. Yatskievych Per. Comm.), dark shading indicates the Delaware County Record (Ruch et al. 1999 specimen BSUH 8227), and the star indicates the county record for Johnson County.
Table 1.--Morphological characteristics and seed production in
Epifagus virginiana in 2013 in Hougham Woods Biological Field Station,
Franklin, IN. (n = 225).

                                Mean    Range        Standard deviation

Height (cm)                     16.1    4.3-40.0            7.3
Distance from Host Trunk (cm)   195.0   18-912              5.1
Number of Branches              6       1-40                6.9
Number of Flowers               61      3-471               80.6
Capsule Weight (mg)             14.00   8.00-20.80          0.0
Seeds                           6.18    1.00-12.00          0.0
Number of Seeds                 827     188-1799           344.6
Weight per Seed ([micro]g)      7.38    3.89-10.74   1.81 x [10.sup.-6]

Table 2.--Presence of chasmogamous and cleistogamous
flowers on Epifagus virginiana in 2013 in
Hougham Woods Biological Field Station, Franklin,
IN. (n = 32).

                     Flower type
Plant
height (cm)   Chasmogamous   Cleistogamous

5.0-10.9           0              12
11.0-15.9          0              34
16.0-20.9          3              68
21.0-25.9          8              114
26.0-30.9          18             249

Table 3.--Host tree metrics and Epifagus virginiana
association in Hougham Woods Biological
Field Station, Franklin, IN. DBH = diameter at
breast height.

              Epifagus       Mean height    Mean distance
             virginiana          of        from host trunk
DBH (cm)  population size    plants (cm)        (cm)

13.3            13              15.0             89.7
14.9             2              16.2            254.2
16.1            16              15.3            185.6
17.1             1              18.2            237.2
18.9             7              13.0            242.3
20.6             1              17.4            276.1
24.3             3              19.3             36.2
33.7             3               7.9             43.2
36.5            34              15.9            191.4
39.9             1              16.5            295.6
46.4           190              19.9            267.0
48.6            18              15.6             57.5
48.8            23              10.1             75.7
55.8            18              17.1            220.1
57.9            40              15.5            139.9
61.5            15              24.6            286.5
63.5           470              16.0            281.7
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Author:Wesche, Spencer L.; Barker, Elizabeth L.; Heikens, Alice L.
Publication:Proceedings of the Indiana Academy of Science
Article Type:Report
Geographic Code:1USA
Date:Nov 22, 2016
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