The Deadly Relationship Between a Vine and a Mint

“Conservation in Progress” is a biannual summary posted on the Bok Tower Gardens website as a rare plant informational tool for website visitors. A few highlights of the Rare Plant Conservation Program’s efforts from January – June 2019: When love kills: the deadly relationship between a vine and a mint The endangered Lakela’s Mint (Dicerandra immaculata) remains in just five scattered, small fragments of scrub habitat along a three-mile stretch of the Atlantic coastal ridge along Florida’s southeast coast. The elevated, sandy areas of scrub habitat are also prime locations for development and citrus groves, and most of the historical mint locations have been destroyed by development. Survival of the remaining mint is dependent upon preserving the quality of the habitat where it still can be found. Maintaining scrub habitat was historically achieved by periodic fire. However, the extant Lakela’s Mint sites are currently difficult to manage by fire because of their urban surroundings. As a result, these sites have experienced heavy overgrowth of both native and invasive species. One of the biggest threats to the survival of Lakela’s Mint is the love vine, Cassytha filiformis. This is a leafless, climbing vine in the Lauraceae family which parasitizes a wide variety of primarily woody plants throughout the tropics and subtropics worldwide in primarily coastal areas. Special structures called haustoria adhere onto and penetrate the cell wall of host plants, extracting vital nutrients and starving the host. Some species are more vulnerable to the love vine than others. Lakela’s Mint is unfortunately extremely vulnerable, and large expanses of mints have perished within weeks of encroachment by love vine (as illustrated in the photo, which shows dead mint plants within an experimental Quadrat and in surrounding areas that are covered with mounds of love vine). Unchecked by fire or other actions, the love vine could easily lead to the extinction of the mint. Bok Tower Gardens and St. Lucie County’s Environmental Resources staff organize monthly half- day volunteer events to remove the love vine by hand. The vine is tediously picked from mint stems, and large handfuls are pulled from surrounding vegetation. All pieces of the vine, no matter how tiny, are diligently placed into bags that are then removed from the site, in order to prevent re-infestation. During the first event in 2017, ten volunteers removed 12 large yard waste bags full of love vine from the mints in less than two hours! Since then, love vine has been cleared from more than two-thirds of the mint population, and mint survival has drastically improved. However, because it can repopulate an area in just a few short months, ongoing, regular efforts to remove the love vine will be reQuired to ensure survival of the Lakela’s Mint. “. like a horse and carriage” It isn’t always obvious, but horticulture and conservation biology are important partners. For example, in early 2019, the RPCP was contacted to conduct a rare plant rescue on a future construction site. Among the species to be rescued were a number of Chionanthus pygmaeus (pygmy fringetree), which is a deciduous woody shrub that grows to about five feet in height. At the rescue, which took place in early March, nine leafless C. pygmaeus were “balled and burlapped”. This basic horticultural techniQue involves digging up a ball of soil surrounding the roots of the plant and wrapping it in burlap. Once the plants reach their destination, the burlap-wrapped root balls are planted whole—burlap and all. As the tree establishes itself, the roots of the tree grow through the burlap, and the burlap decays. This method is useful for moving large shrubs and trees, as it reduces root disturbance compared to planting the plant in a plastic pot, which then must be removed. As of May 2019, all nine of the C. pygmaeus had leafed out and were growing. An additional factor contributed to the success of this rescue: timing. As a general horticultural rule of thumb, deciduous shrubs and trees are most successfully transplanted when they are dormant. Transplanting a tree removes most of its root system, and therefore most of its ability to absorb water from the soil. Leaves are a major source of water loss for plants, and so if there are no leaves, water loss is reduced. Additionally, the dormant season tends to be cooler, which also reduces evaporation. Had this rescue taken place a month or two later, the survival of the plants would have been much less assured. Although this construction project was not scheduled with the wellbeing of the plants in mind, its fortuitous timing highlights the importance of considering basic horticultural knowledge when planning projects that will reQuire transplanting endangered plant species. Multi-faceted research into a rare pawpaw The Rare Plant Conservation Program is partnering with Missouri Botanic Garden, Nova Southeastern University, Dr. Eliane Norman, YBE Consulting, the U.S. Fish and Wildlife Service, the Florida Forest Service and the Cincinnati Zoo on a multi-faceted project to better understand and preserve the rare Rugel’s Pawpaw, Deeringothamnus rugelii. This species is found only in upland, scrubby flatwoods in Volusia County. During this project, surveys and population updates are taking place for all known populations. Because few to no seeds are observed in the wild, tissue culture techniQues are being used to propagate clones of all remaining populations and cryopreserve genotypes. Novel research has been initiated on population genetic structure, microhabitat requirements, and microbiome communities. Tissue culture-produced plants will be used to establish a new population on protected land. During April-May 2019, visits were made to several populations, some of which hadn’t been visited for decades, for population updates and mapping, and the collection of leaves, cuttings and soil. Pictured are Dr. Christy Edwards (Missouri Botanic Garden) and Mike Jenkins (Florida Forest Service) during leaf collection from a long-unvisited population in April. Big Partnership Conserves Big Trees In May 2019, Bok Tower Gardens’ Rare Plant Curator Phil Gonsiska attended the Center for Plant Conservation’s annual meeting, held this year at the Chicago Botanic Garden. One of many highlights of the meeting was a tour of the Morton Arboretum. The Morton Arboretum is one of the 20 institutions participating in the American Public Gardens Association Plant Collections Network’s accredited multisite ex situ collection of Quercus (oaks). Oak conservation is problematic for a number of reasons, one of which is the fact that the seeds are recalcitrant. Upon maturing, most seeds dry down to a fraction of their previous water content. These seeds are termed “orthodox,” and they can ii be stored in controlled conditions as seeds for an extended period—sometimes decades or centuries. All of the seeds home gardeners encounter at Lowe’s or Home Depot are orthodox. Recalcitrant seeds, on the other hand, die when they start to dry out and so can only be stored for days or weeks. Although research is being done on ways to store recalcitrant species in liQuid nitrogen, these methods are currently not practical for the vast majority of recalcitrant species or the institutions trying to conserve them. Recalcitrant species must, therefore, be stored as whole, actively growing plants. This raises two of the other complications involved in oak conservation: they grow in a wide variety of climates, and many species are very large trees. This highlights the importance of multisite collections. Different institutions in different climates can specialize in Quercus species that grow in those climates, and no one institution must maintain the large pieces of property necessary to house these plants. Although Bok Tower Gardens is not a member of this group, it is assisting the Missouri Botanical Garden in its efforts to conserve Quercus arkansana, an endangered oak from the southeastern United States. In 2018, the Missouri Botanical Garden sent seeds of Q. arkansana to BTG to be grown as a backup collection of this species. When they have grown large enough, some of these plants will be housed in the National Collection, and others will be planted in the public garden to fulfill the purposes of conservation, public education, and enjoyment. Germplasm preservation of the rare and endangered herb, Lewton’s Polygala In April, seeds from the state and federally endangered Florida endemic, Lewton’s Polygala (Polygala lewtonii) (Polygalaceae – Milkwort Family) were collected from a natural population for ex situ preservation into our Center for Plant Conservation National Collection. Lewton’s Polygala is a small herb found in upland Sandhill habitat. The species can easily go unnoticed due to its small size, even when in full bloom. The interesting little pink flowers have two small dorsal petals and a third petal adorned with a feather-like crest. Plants are typically found in small colonies or clusters, not often scattered about with individual plants far from one another. It is believed that plants exist in these colonies because ants likely disperse the seeds, and the ants are only able to carry seeds short distances from the parent plant. Additional evidence that suggests the seeds are dispersed by ants is the presence of an elaiosome attached to the fruit. Pictured here is a magnified view of a Lewton’s Polygala fruit. The fruit (testa) is brownish-black colored and covered in fuzzy white hairs. The elaiosome is a lipid-rich, wing-like tissue attached to the fruit and serves as a nutritious attractant for the ants. A fascinating symbiotic relationship, where the ant is rewarded with nutritive tissue and the plant is aided in dispersing seeds. iii Research into its genetic by Missouri Botanical Garden and Archbold Biological Station suggests that plants in close proximity or within the same subpopulation are genetically similar, and that subpopulations are genetically distinct from one another.

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