Integrating genetics, morphology, and fungal host specificity in conservation studies of a vulnerable, selfing, mycoheterotrophic orchid (Corallorhiza bentleyi Freudenst.)

March 17, 2021

Mycoheterotrophic plants derive most or all carbon and nutrients from fungal partners and represent poorly understood components of forest biodiversity. Many are rare or endangered yet can be ecological indicators of forest ecosystem function due to fungal host requirements. One such species is the IUCN red-listed (‘vulnerable’), fully mycoheterotrophic orchid, Corallorhiza bentleyi. This recently described species is among the rarest plants in Appalachia, known from five counties in Virginia and West Virginia. The species has a restricted range, small population size, and is self-pollinating. Here, an integrative approach was taken in conservation genetic assessment of C. bentleyi using floral morphometrics, simple-sequence repeats, and fungal host DNA to characterize variation within and among sampling localities. Morphology reveals differentiation among individuals from six sampling localities. Surprisingly, most genetic variation is found within localities, contrary to the expectation for a selfing species. Fungal host DNA reveals extreme specificity upon a few genotypes of a single ectomycorrhizal host species, Tomentella fuscocinerea, across all localities. We discuss conservation implications of morphological, genetic, and symbiotic diversity in this vulnerable species, and recommend additional assessment of conservation status based on: an obligate reproductive mode of selfing, preventing benefits of outcrossing among genetically non-identical individuals; extreme host specificity, severely restricting niche space; and highly fragmented habitat under threat from anthropogenic disturbance. This study underscores the importance of integrative conservation assessment, analyzing multiple data sources, and reveals patterns not readily apparent from census-based assessments alone.

Scientific Note: Dictyostelid Cellular Slime Molds Associated with Limestone and Dolomite Glades in Northwest Arkansas

April 11, 2021

Samples for isolation of dictyostelid cellular slime molds (dictyostelids) were collected from two types of glades (limestone and dolomite) in northwest Arkansas. Glades are non-forest habitats which typically have shallow and usually rather xeric soils. As such, they would not appear to be particularly suitable for dictyostelids. In the present study, only seven species were recovered, and just three of these were recorded from both limestone and dolomite glades. Total densities (clones/gram) were rather low for both types of glades, with 25 clones/gram in dolomite glades and 23 clones/gram in limestone glades.

Myxomycetes Recorded from the Vicinity of the Mountain Lake Biological Station

April 11, 2021

Myxomycetes (plasmodial slime molds or myxogastrids) have been collected in the Mountain Lake area of southwestern Virginia since 1890, and several recognized authorities on this group of organisms along with numerous other individuals have visited or worked at the University of Virginia Mountain Lake Biological Station. The collective efforts of all these individuals have generated a considerable body of information on myxomycetes. The purpose of this paper is to provide a comprehensive annotated checklist of all species of myxomycetes reported from the Mountain Lake area. This checklist contains 166 species in 39 genera. This total is approximately 36% of the total number of species of myxomycetes known from all the eastern United States and is likely to be higher than the total recorded for any area of comparable size in the entire country and perhaps the entire world.

Responses of Florida Scrub Vegetation to Water Additions from a Groundwater Treatment Project and to Hurricane Disturbance

April 11, 2021

Florida scrub is a fire-maintained shrub vegetation of well-drained, sandy soils; dominant species include several species of Quercus and Serenoa repens. In a remediation project, treated groundwater was distributed through an exfiltration gallery into intact scrub. We established eight permanent line-intercept transects (15 m length) in the site in April 2002, four close to the exfiltration gallery and four more distant from it. We sampled vegetation, <0.5 m and ≥0.5 m, along each transect and measured vegetation height at four points (0, 5, 10, 15 m) annually through 2019. The initial phase of the project operated from October 2002 to early March 2004 (494 days) and distributed 1.74 × 10⁸ L of water. The final phase of the project occurred from March 2005 through August 2008 (1,251 days) and distributed 1.90 × 10⁸ L of water. Pumping raised the water table near the exfiltration gallery. Vegetation height did not differ between the near and far transects initially. Vegetation height increased in the near transects by 2004 with the greatest percent change in 2003 and 2004 as did total cover ≥0.5 m. Total cover <0.5 m and bare ground were similar initially in the near and far transects and declined in the near transects by 2004. Scrub species, particularly the dominant scrub oaks, increased height and cover in response to water additions with no loss of dominant scrub species and no establishment of mesophytes. Hurricane Frances (September 2004) reduced cover ≥0.5 m the following year. Hurricane Matthew (October 2016) and Hurricane Irma (September 2017) caused greater damage including breaking limbs as reflected in reduced height and total cover ≥0.5 m probably because the older, taller scrub was more vulnerable to wind damage.

Long-term Demography Study of Trillium pusillum var. pusillum Following Hurricane Hugo in 1989

April 18, 2021

Hurricane Hugo was a category five storm in September of 1989 that significantly impacted natural areas along the Carolina coastal plain through wind damage and storm surge flooding. Francis Beidler Forest, an Audubon wildlife sanctuary in Four Holes Swamp, suffered severe damage to its forest canopy. In response to concerns that the rare spring ephemeral Trillium pusillum var. pusillum may be negatively impacted by the loss of the mixed hardwood canopy, we established permanent plots in the spring of 1990 with single leaf, triple leaf, and flowering individuals recorded by Ecology faculty and students at The Citadel. Disruption to the forest canopy would significantly alter forest floor microhabitat conditions negatively affecting T. pusillum var. pusillum population demography. There was no expected negative effect of Hurricane Hugo, and the loss of canopy cover on the population. Evidence suggests that the decrease in canopy cover and increased light was associated with increased flowering. The coefficient of variation, as a measure of cohort variability among years, increased from flowering, to triple leaf, to single leaf across the 29 years of population monitoring. There was a significant positive association between the number of named storms in the previous two and three years and the number of single leaf plants. There was no evidence that the population is decreasing, even though the number of flowering individuals has decreased. The results of this long-term demography suggest that even severe natural disturbances, like hurricanes and tropical storms, may have a positive effect on Trillium population dynamics.

A Floral Checklist for Wheaton Regional Park, Montgomery County, Maryland

May 10, 2021

Wheaton Regional Park is a suburban 500-acre park in Montgomery County, Maryland, on the northern edge of the Washington, D.C., metropolitan area. Early floristic surveys of the park, conducted between 1961–1964 when the park was founded, showed the park to be diverse, with 443 taxa of vascular plants. Our research team conducted a second round of floristic surveys between 2014–2019 to update the checklist of plants in the park. Here, we present a comprehensive checklist of all species collected in the park over the past 50 years, discuss recent plant introductions, and share a platform for a digital flora of the park through the Mid-Atlantic Megalopolis online portal. We documented 393 vascular plant species from the 1960s, as part of a comprehensive review of those collections. The 2010s collections recorded 293 vascular plant species, and an additional 16 species of bryophytes. In total, 554 species of plants (vascular and non-vascular) in 326 genera and 118 families have been recorded in Wheaton Regional Park over the past 50 years. We found that the surveys in the 2010s identified a substantial number of vascular plant species that were not recorded in the 1960s surveys. Additionally, we were able to recover less than half of the vascular plants recorded in the 1960s. The proportion of non-native vascular plant species increased from 22.1% in the 1960s to 34.5% in the 2010s. We offer recommendations for preserving the extant diversity of native plants in the park.