CPC Plant Profile: Florida Filmy Fern
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Plant Profile

Florida Filmy Fern (Trichomanes punctatum ssp. floridanum)

Trichomanes punctatum ssp. floridanum blankets a limestone wall in a Miami-Dade County preserve. Photo Credit: J. Possley
Description
  • Global Rank: T1 - Critically Imperiled
  • Legal Status: Federally Endangered
  • Family: Hymenophyllaceae
  • State: FL
  • Nature Serve ID: 157685
  • Date Inducted in National Collection: 12/07/2021

A perennial, mat forming fern with creeping rhizomes and tiny, highly variable leaves which linear, round, or lobed but do not exceed 2m in length.  As with all members of the Hymenophyllaceae family, it's leaves are membranous and may shrivel up or disappear during drought. It's fronds are fertile and contain a soral involucre at the leaf margin, which consists of sporangia and the "bristle" that is referenced in the common name of this species. Gametophytes are green in coloration, filamentous, resembling algae, and may reproduce asexually by means of gemmae. This species disperses spores via wind and likely through water as well. T. punctatum ssp. floridanum is a globally very rare subspecies of the tropical species Trichomanes punctatum.  The sub-species is found only in two far disjunct locations in Florida.  The two Sumter County populations contain more material (pers. comm., Craig van der Heiden), but their protection from development is questionable.  Fairchild has estimated that the four known Miami-Dade County populations cover only about ten square meters.  When one considers this taxons’ very narrow range and narrow habitat niche in combination with extreme difficulty of collecting spores and with cultivation, it seems that recovery may be a difficult task.

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    Updates
    • 02/07/2018
    • Propagation Research

    There is little to no material currently available for outplanting. Fairchild, CREW, and Marie Selby Botanical Gardens have all grown material propagated from cuttings collected by Fairchild from CASH in 2005. In all cases, agencies reported that the taxon is difficult to grow, and collections dwindled from poor health. At Fairchild, we maintained fewer than 10 colonies in small pots in terraria, but they were very susceptible to mold and fungus, did not appear to produce any new growth, never sporulated, and leaves took on a very linear form that looks very different from wild plants.   

    Should healthy material become available, outplanting at extant sites in Dade (CASH, HBH, FUH, MSH) would promote conservation of this taxon, and plantings in additional habitat within the species’ historic range could also include CASR, CDE, BSP, HRD, and possibly other Miami-Dade County preserves.

    • 02/07/2018

    It is important that Fairchild continue to annual monitoring of all Miami-Dade populations for health and sporolation.  It is also essential that the Institute for Regional Conservation take the same measures with populations in Sumter County.

    The development of collection methods and the identification and photography of gametophytes in the wild  by Fairchild, IRC, and others is another needed action.

     Fairchild, and possibly others must determine whether this taxon is still present in the remnants of the former Cox hammock, obtain permissions to collect cutting and spores (ff available) for ex situ conservation.

    • 02/07/2018

    In most cases, current management by Miami-Dade County Natural Areas Management (NAM) appears to be sufficient to maintain the population at current levels.  However, augmenting current populations and increasing groundwater and humidity in high quality hammock sites may be the only way to sustain this species in the wild.

    • 02/07/2018

    Actions that are currently a priority include:

    • Conducting a search for new occurrences, all potentially suitable habitats in and around Sumter County, and historically occupied areas in Miami-Dade County where this species can thrive.
    • Continued removal of exotic plants from current habitats and immediate restoration of the canopy cover (with shade cloth if needed) over existing colonies after hurricane and other damaging  events which may cause loss of canopy cover.
    • Exploring the potential benefits of watering of colonies during extended drought periods as well as investigating the feasibility of pumping water into hammock solution holes that support rare ferns in order to increase water and humidity levels.
    • Augmentation of existing occurrences and reintroduction of extirpated occurrences through outplantings, continued protection of habitats from public use, and long term monitoring of all occurrences.
    • Initiation of life history and genetics studies; information covering longevity, growth rates, recruitment rates, reproductive requirements, dispersal methods, and genetic variation is specifically needed.
    • Assessing the extent in which fungus may be a threat in the wild.
    • Promoting a higher regional water table on the Miami Rock Ridge.
    • Establishing a monitoring program at Withlacoochee State Forest.

    • 02/07/2018
    • Genetic Research

    A genetic analysis of tissue from all known Florida populations was conducted by Colin Hughes of Florida State University in order to determine how closely related to one another they are. He compared sequences of of one particular gene locus and his preliminary results showed that the different populations are "genetically indistinguishable" at that particular locus.

    • 02/07/2018

    As of April 2014, USFWS has developed an unpublished recovery plan for T.punctatum ssp. floridanum recommending the following conservation methods (USFWS 2012):

    Increasing the ground water table level under hammocks would be the most beneficial to this taxon along with the current population of the Florida bristle fern; unfortunately, this option is not feasible because a raise in ground water levels would increase the risk of flooding in populated areas and agricultural lands.

    • 02/07/2018

    Cuban garden snails have been introduced into this habitat but have not been observed eating this species. However, they have been known to impact other native ferns in the area making herbivory a possible concern.

    • 02/07/2018

    Valerie Pence, at CREW has investigated the optimal propagation protocols for vegetative propagation of  T. punctatum ssp. floridanum sporophytes. CREW has also grown plants clonally, in vitro, and from wild-collected cuttings.
     

    • 02/07/2018

    Accidental impact by on-site vegetation management crews is possible, such as off-target herbicide damage, piling of vegetation debris, or removal of non-native overstory species that cause a sudden increase in light and decrease in humidity.

    Off site drainage and lowering of the regional water table may also be a threat to this species.

    • 02/07/2018

    Succession in mature hammocks where T.punctatum ssp. floridanum is found is rarely a problem, although succession due to gap openings (caused by storms or weed removal) is a serious threat.

    • 02/07/2018

    Non-native invasive weeds are serious threats and include the following species in Miami-Dade County: Epipremnum pinnatum, Syngonium podophyllum, Thelypteris opulenta, Nephrolepis cordifolia, and Dioscorea bulbifera.

    • 02/06/2018

    Slope movement is a serious threat and could negatively impact, or even eliminate a colony of this species.

    Although fire is not a significant threat in hammocks, it would still potentially cause mortality.
     

    • 02/06/2018

     Hurricanes decrease hammock canopy cover, likely leading to increased light levels and decreased moisture levels within forests, which would negatively impact T. punctatum ssp. floridanum. Major hurricanes could cause mortality.
     

    Nature Serve Biotics
    • 05/02/2017

    SUBSPECIES EXTREMELY RARE AND PROTECTED ON ONLY A FEW MANAGED AREAS, WHERE IT IS THREATENED BY EXOTIC PEST PLANTS.

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    Nomenclature
    Taxon Trichomanes punctatum ssp. floridanum
    Authority W. Boer
    Family Hymenophyllaceae
    CPC Number 44659
    ITIS 17917
    USDA TRPUF
    Common Names Florida Bristle fern | dotted bristle fern
    Associated Scientific Names Didymoglossum punctatum | Trichomanes punctatum | Trichomanes punctatum ssp. floridanum
    Distribution Historically and currently, Trichomanes punctatum ssp. floridanum is endemic to both Sumter and Miami-Dade counties in South Florida.

    It is currently known to be present in four preserves in Miami-Dade county (CASH, FUH, HBH and MSH) as well as two locations in Sumter Country (USFWS 2012).

    In 2014, Fairchild estimated that the Miami-Dade germplasm consists of approximately 10 square meters of material in 10 separate geologic features across the four preserves. The majority of the germplasm (8.75 sq m) is in CASH, followed by MSH (0.86 sq m), FUH (0.22 sq m) and HSB (0.08 sq m).
    State Rank
    State State Rank
    Florida S1
    Habitat

    This species can be found in Rockland Hammock solution holes and can also grow limestone or vertical or horizontal roots and rocks, although it is rare that it will be found on tree roots. It requires high humidity and requires full shade as it's fronds are sensitive and will burn if in direct sunlight for more than an hour or two.

    Ecological Relationships

    In Miami-Dade County, this species is associated with mature rockland hammock tree species in the overstory (e.g. Lysiloma latisiliquum, Ficus aurea, Bursera simarouba, etc), as well as other native lithophytic ferns in the understory (e.g., Ctenitis sloanei, Asplenium dentatum).

    T.punctatum ssp. floridanum is almost always associated with bryophytes and is also known have a mutual support for epiphyllous bryophytes as well.



     

    Pollinators
    Common Name Name in Text Association Type Source InteractionID

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