Inside the Center for Plant Conservation

This story first appeared in the August 2005 issue of Horticulture.

Stern’s medlar (Mespilus canescens) is a botanical mystery. A tall, darkly handsome shrub with rich bluegreen deciduous leaves and a brief but dazzling spring display of snowy white flowers, this member of the rose family (Rosaceae) was first identified as a species as recently as 1990. It is known from a single population of 25 or so individuals in a 22-acre deciduous grove in rural Arkansas. The only other Mespilus species is native to Europe and Asia Minor. Now, thanks to conservation botanists at the Missouri Botanical Garden in St. Louis, a lush specimen of this rare native graces the entrance to the garden’s Emerson Conservation Center, home to the offices of the Center for Plant Conservation (CPC). A nearby greenhouse harbors rooted cuttings taken from the wild population, and, because the plant has not been observed to set fruit in the wild in many years, work is underway to propagate the species by tissue culture.

‘For a teeny-tiny office, we have been a force in conservation biology,” asserts CPC president and executive director Kathryn L. Kennedy. Though the office operates with a staff of six or fewer, the nonprofit CPC, founded in 1984, comprises a network of 34 participating botanical institutions, located in Hawaii, across the continental United States, and the U.S. Virgin Islands. Together they maintain the National Collection of Rare and Endangered Plants and oversee programs aimed at stabilizing or restoring these plants in the wild. “The goal of the national office is to grow these programs,” says Kennedy. Overseen by an independent, volunteer board of trustees, the CPC is selective. Prospective network members must agree to follow prescribed conservation practices and protocol. “We want commitment from our network institutions,” explains Kennedy. “It can take 20 to 30 years to do research, establish habitat, restore plants, and do follow-up until a population is stable. You’re often looking at a 30-year time frame.rsquo;


The National Collection of Rare and Endangered Plants consists of seeds and other plant material of over 600 imperiled native species. As partners in the recovery of species under their care, member institutions bank seeds on-site or arrange long-term seed storage at such facilities as the Department of Agriculture’s National Center for Genetic Resources Preservation at Fort Collins, Colorado, and the Center for Urban Horticulture’s new Miller Seed Vault at the University of Washington in Seattle.

In recent years the CPC’s primary mission has expanded beyond that of living library to an ultimate goal of restoring vigorous natural populations. “The best place to save plants is in the wild, where there’s more variability,” Kennedy notes. “With a static collection there are inbreeding problems.” And seed saving doesn’t work with all plants, according to Kennedy. Some tropical seed, for instance, doesn’t store well, and it can take years to collect a sufficient quantity of seed of extremely rare plants, because few seeds can be safely harvested at a time. Plants that are difficult to propagate by traditional methods are increased by tissue culture, either at an appropriately equipped CPC institution, such as the University of Hawaii’s Harold L. Lyon Arboretum in Honolulu, or at the Cincinnati Zoo and Botanical Garden’s Center for Conservation and Research of Endangered Wildlife.


To date, Robbins’ cinquefoil (Potentilla robbinsiana) is the CPC’s most celebrated success story. This tiny, long-lived, alpine perennial—known from only three populations at two sites in the rugged White Mountains of New Hampshire—was threatened by overcollection and inadvertent trampling by hikers until the New England Wild Flower Society, a CPC participating institution, came to the rescue, along with other interested groups. Hiking trails were rerouted, and society members learned to germinate the seed offsite, cultivate resultant seedlings under nursery conditions, and transplant them into the wild, both at original and additional sites. A cold storage seed bank was also established for the species. With the plant’s numbers increasing to over 14,000 individuals, it was removed from the federal Endangered Species list in 2002.

‘I love working with the CPC. It’s very fulfilling,” says Anita Tiller, a botanist with network member Mercer Arboretum and Botanic Gardens in Humble, Texas. Tiller is especially enthusiastic about preserving native plants of the Texas coastal prairies, which are increasingly overrun by development. “I’m pretty passionate about this. We’ve got to make sure a little bit of native prairie is left for future generations,” she says.

One of Tiller’s current pets is prairie dawn (Hymenoxys texana), a low-growing annual composite that produces a profusion of small, globular heads of yellow disk flowers in spring. Thought to be extinct until its rediscovery in 1981, it has a preference for seasonally wet depressions and saline swales bordering low, thinly vegetated pimple or mima mounds, where it associates with the similarly rare Texas windmill grass (Chloris texensis) and the golden-flowered Houston camphor daisy (Rayjacksonia aurea). All three are among the two dozen National Collection plants in Mercer’s watchful care. Many of these can be seen in the arboretum’s newly expanded Endangered Species Garden.


So devoted to the goals of the CPC is Tiller that, as a memorial to her parents, she recently joined co-worker Suzzanne Chapman and other Mercer friends and volunteers, area garden clubs, and charitable societies in funding a full CPC sponsorship for the federally listed Texas trailing phlox (Phlox nivalis subsp. texensis), a showy, needle-leaved, creeping subshrub endemic to the once expansive longleaf pine savannas of southeastern Texas.

‘The Center for Plant Conservation is supported almost totally by donations and grants,” explains Kennedy. “The beauty of the sponsorship program is that it supplies stable, sustained funding.” A full sponsorship, which consists of a one-time investment of $10,000, endows a fund that provides annual payments to a member institution to assist in the study, maintenance, and restoration to the wild of a plant in its care. While many National Collection plants are fully or partially sponsored, many others—even Stern’s medlar—remain sponsorless poster children for plant conservation.

Not surprisingly, funding cutbacks can be a problem, but so far only one member institution, the Nebraska Statewide Arboretum, has been forced to withdraw from the network. “We’re hoping Nebraska can come back,” says Kennedy. “They withdrew because they feared they couldn’t do the work they needed to do to save the species in their care.” In the meantime, responsibility for these species has been shifted to other member institutions.


Kennedy considers the CPC fortunate to have recently initiated a partnership with the conservation-conscious American Horticultural Society in an effort to involve gardeners in plant conservation. She has a ready answer for anyone who asks why it’s worthwhile to go to so much trouble to save plants that may or may not project obvious garden potential. “These plants are intrinsically valuable for the ecological roles that they play. Seldom are there species imperiled without the rest of the system being imperiled as well.rsquo;

She notes the accelerated rate of decline resulting from habitat degradation and points out that the loss of vegetation negatively affects vital ecosystem cycles, from water quality to wildlife support. “Even if you don’t give a fig about plants and don’t see this connection, you should still be concerned, because plants have economic value,” she says. “Food, flavorings, fiber, fuel—plants give us so many gifts. Many wild plants are related to economically important crop plants. If you’re looking for a plant trait to resist disease or drought, go back to the wild. I predict that in the next hundred years, plants of the American West are going to be important resources in dealing with the problems of global warming, such as salinization. It makes no sense at all to lose our own indigenous species when it’s completely unnecessary. These plants can be saved and should be.rsquo;

The CPC works closely with state and federal agencies, and increasingly, Kennedy and other center representatives journey to Washington to practice “gentle advocacy,” reminding elected officials and agency managers that saving plants is just as critical as saving animals. “It’s important for people to understand that these are vital natural resources, and vigilance and restoration are needed. People are going to have to pay attention to government spending. We’re going to lose a legacy that has untold value for future generations. We’ve got to let our legislators know that we support spending to save these resources. Future generations will look back in great anger if we let their heritage disappear. It’s their future we’re bankrupting.”

Visit the CPC website

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