Plant Conservation Program
Native Orchid Conservation at Longwood Gardens
In 1906 industrialist Pierre S. du Pont purchased a farm near Kennett Square, Pennsylvania, to save a collection of rare and historic trees. Conservation was the inspiration for purchasing the land that would become Longwood Gardens; since that time, plant conservation practices have been an informal tradition at Longwood. Examples include maintenance and propagation of one of the world’s rarest cycads, Encephalartos woodii; the display and development of one of the largest orchid collections in North America, and many similar stories. To promote our active and longstanding role in conservation and preservation, we have established a new Plant Conservation Program, with a focus on our dedication to rare, unusual, and beautiful plants from around the world.
To build upon our world class collection of Conservatory orchids and to introduce orchids to outside areas of the Gardens and natural lands, we have begun to grow the collection in a new and meaningful way. We are expanding our public outreach and working to conserve Pennsylvania native orchids in Chester County, throughout the state, and across the country through innovative and responsible propagation, cultivation, and display. Pennsylvania has about 55 species of native orchids, nearly half of which are considered rare, threatened, or endangered. As members of native plant communities, these orchids serve as indicators of environmental quality due to their network of complex interactions with pollinators, soil fungi, and natural variations in environmental conditions.
For example, the tiny dust-like seeds that characterize all orchid species must come into contact with a symbiotic fungal species in order for the seeds to germinate, grow, and survive. This complex natural relationship translates into a horticultural protocol for germinating the seeds, which requires the use of specialized laboratory techniques in order to grow them in cultivation. For many species this information exists, but for others it is virtually unknown. All of these factors have contributed to the development of our Plant Conservation Program.
Our project goals include seed collection, in vitro (laboratory) seed propagation, establishing protocols for seedling production and development, establishment of ex situ orchid populations at Longwood Gardens, and restoration of native orchid populations using seedlings raised in our laboratory. To help achieve these goals, we are collaborating with several institutions with expertise in native orchid propagation, horticulture, and ecology: The Pennsylvania Department of Conservation and Natural Resources, Mt. Cuba Center, The Brandywine Conservancy and Museum, and the Native American Orchid Conservation Center (NAOCC). Work began in 2015, and collectively we have identified several species of interest. Here are a few case studies of work in progress.
Cypripedium parviflorum var. pubescens, the large yellow lady’s slipper in Chester County, Pennsylvania
Native orchids have always been considered difficult to propagate. Take the popular lady’s slipper (Cypripedium). Commercial propagation of these highly desirable, showy orchids was one of the major breakthroughs of the last 25 years. However, even though many species are now commercially available, some idiosyncrasies concerning their propagation remain, and many of the plants in cultivation cannot be tied to a place of origin—thus lacking conservation value. A good example is one of the most widespread U.S. and North American native species, the large yellow lady’s slipper (Cypripedium parviflorum var. pubescens). It is recognizable and well-known, a flagship species among over 200 North American native orchids. Although distributed from the U.S. east coast to Alaska, this species has become rare in many areas, including right here in Chester County.
There appears to be only two remaining populations of this species in Chester County. One of them is a small population on a Brandywine Conservancy property, not far from Longwood Gardens, that served as a motivating factor for our Conservation Program. We received permission to collect seeds from this population, but seed propagation is not always straightforward. To overcome potential problems, we tried two seed propagation techniques using mature and immature (partially developed) seeds. So far we have found that hand pollinating the flowers and harvesting the partially developed seed capsule at 50 days after pollination gives the best germination and continued development of seedlings.
We have been successful in raising hundreds of seedlings from this population, as well as from another population near Birchrunville in Chester County, and from cultivated plants at Mt. Cuba Center. Despite our initial success, lady’s slipper orchids are slow growing and take 3-6 years or more until they first flower. We anticipate planting the first lady’s slippers in the Hillside Garden in 2018. We are expanding our seed propagation efforts to other Cypripedium species too, with the hope that we can one day display a broad range of species in the Gardens.
Platanthera, also known as fringed orchids, represent one of the largest natural groups of North American native orchids and are possibly the showiest of the summer flowering orchids. Yet despite their popularity with native orchid enthusiasts and botanists, they remain a poorly understood group by horticulturists and little is known about their seed propagation and cultivation. Many species are of conservation concern, possess horticultural value, and have the potential to fill the need for more summer flowering orchids at Longwood. We've started to work with a few different taxa including P. peramoena, the purple fringeless orchid, and P. ×bicolor, a very rare naturally occurring hybrid on the edge of existence in Pennsylvania. We're developing seed propagation and seedling development protocols to learn how these orchids can be grown for conservation and display purposes.
Spiranthes casei var. casei, Case’s lady tresses
There are more species of Spiranthes, known as lady’s tresses, in eastern North America than anywhere else in the world. One of these, Spiranthes casei, named after Michigan botanist and horticulturist Fred Case, is one of Pennsylvania’s rarest native orchids and grows in a region of the State where fracking has become commonplace. Spiranthes are generally species of disturbed sites and S. casei is no exception; its favored habitat in north central Pennsylvania is mowed roadsides that are at risk from activities related to fracking operations. We were contacted by botanists from the Elk State Forest, who wanted to be proactive in the conservation of this species and propagate it for reintroduction to different areas of the forest.
Little has been written about Spiranthes seed propagation, with sources disagreeing about its degree of difficulty. We collected seeds in November 2015, and through targeted experimentation, we generated a protocol for seed germination and propagation that we hope will serve as a template for other Spiranthes species of conservation concern in the United States. We also hope to apply this work at Longwood Gardens, where a handful of Spiranthes vernalis, a PA state endangered species, was discovered growing in a remote corner of our Natural Lands. We will apply our newfound knowledge to the propagation of S. vernalis during the coming season, with the hope that we can increase the numbers and sustainability of our small population.
Future of the Program
We will continue to expand our work with native orchids in Pennsylvania, the mid-Atlantic, across the United States, and beyond. In Pennsylvania, we have worked with our collaborators to create a list of target taxa and have begun work with other Pennsylvania rare and endangered species such as Arethusa bulbosa, Goodyera tesselata, and other Platanthera taxa. We will also take our work to the international stage as we develop a program with the Vallarta Botanical Gardens to work on rare orchids in Jalisco, Mexico. Stay tuned!