Many plant species native to New York also grow in climates that are drastically different from ours. For example, wild bergamot’s (Monarda fistulosa) native range extends through Canada and nearly every state in the continental US. In Mississippi, nursery growers found a population of wild bergamot with a rich petal color and sturdy habit. They propagated plants from this population, trialed them, and marketed them for their resistance to powdery mildew – a fungus that leaves an unsightly white coating on foliage. This variety, M. fistulosa ‘Claire Grace’, has become very popular with gardeners and, in subsequent trials, has continued to show resistance to powdery mildew. However, in northern regions with extremely harsh winters ‘Claire Grace’ does not always demonstrate the same cold hardiness expected from wild bergamot.

The distinct flower color of Claire Grace wild bergamot (Monarda fistulosa ‘Claire Grace’) caught the attention of nursery growers in Mississippi.

Within a species, different populations adapt to their unique environments. These populations are called ecotypes and while the differences from one population to the next may not always be visible, they can play a critical role in each population’s survival. ‘Claire Grace’ evolved to resist powdery mildew, which is prevalent in humid climates like Mississippi’s. However, this southern population would not need to develop the same level of cold tolerance that ecotypes at the northern limits of the species’ range possess. In our gardens, ‘Claire Grace’ gets coated with powdery mildew. Any number of stressors on the High Line – from air pollution to constructed soils – could make this ecotype more susceptible to disease than it would be in its native habitat.

Genetic differences among plants of the same species make the species more resilient. Such genetic diversity means that some populations and individuals can overcome threats that others cannot. How then can we promote genetic diversity? In addition to protecting wild habitats, we can also collect seed from local ecotypes, as Uli Lorimer did for the Native Flora Garden at Brooklyn Botanic Garden. Lorimer says, “We need to recognize that seed is as precious a resource as timber or oil.” Every seed contains a wealth of genetic information and the plant that grows from it will be slightly different from its neighbors. For instance, an individual may have a flower shape that is more conducive to pollination or produce stronger defensive chemicals to protect itself from insect pests. Such diversity is the foundation for evolutionary fitness.

Pollinators may notice plant features that humans do not.Photo by Ayinde Listhrop

In the nursery industry, most plants are not grown from locally collected seed and many plants are not grown from seed at all. Often, plants are produced vegetatively by taking a cutting or dividing the parent plant. Tissue culture is a newer and increasingly common method by which plants are produced from a single cell. In both cases, the new nursery plants will be clones of the parent. These uniform populations will be equally susceptible or resistant to pests and diseases. As the gene pools shrinks the overall population’s resilience shrinks with it.

Many nursery growers are passionate about native plants and aware of the importance of preserving the traits of local ecotypes. However, collecting wild seed is more laborious and time-consuming than other methods of propagation. In an industry with notoriously tight profit margins, most nurseries cannot afford to propagate from wild-collected seed unless there is a high demand from customers for plants produced in this manner. Luckily, in New York City we have the Greenbelt Native Plant Center, a facility of the NYC Parks Department that not only supplies the parks system, but also donates plants to community and school gardens. The nursery grows all its plants from seed collected by Heather Liljengren and her team. Liljengren loves “collecting seeds from really tough urban areas like a vacant lot or polluted waterway; sampling from those plants feels like you are capturing the superpowers of survival for a species.”

Purple milkweed (Asclepias purpurascens) seeds collected on the High Line. Though native, this species is rare in NYC so FHL sometimes shares seed with other institutions.

As wild areas are developed and local ecotypes pushed out, seed collecting takes on new urgency. By saving seed we can at least save some of the character of the plant communities that are threatened or destroyed. Liljengren says, “Every seed I collect is a possible plant to be put back out into the landscape.” The plants from which she collects have not been bred to look pretty, though many of them are stunning. Rather, they have evolved to survive in specific conditions. By collecting and propagating from seeds, we can introduce the wild character of our local ecotypes into New York City’s parks and gardens.

Our horticultural team counts on members and friends like you to help keep the High Line beautiful and thriving. Join our community of supporters who play an essential role in the High Line’s most important gardening projects.

TD Bank is the Presenting Green Sponsor of the High Line.