Since beginning to work on the Nantucket Flora Update project, we have discovered more than 60 plants that are established on Nantucket, but were not included in the most recent island flora, Sorrie and Dunwiddie’s The Vascular and Non-Vascular Flora of Nantucket, Tuckernuck, and Muskeget Islands, published in 1996. While many of these “new to Nantucket” species are obvious garden escapes or invasive weeds that have made themselves at home and spread on their own to new places, a few are a bit more mysterious.
Late this season, I started working on surveying the streets in the core area of downtown Nantucket to search for established plants not already on the list. Most of the botanical research conducted on island occurs on conservation properties, so there has been little targeted exploration of “urbanized” areas on the island. Since starting to work on the Cooperative Nantucket Flora Update, I’ve been exploring areas around parking lots and neighborhoods wherever I happen to go, but I’d never systematically walked all the streets downtown. Aside from the usual well-trodden routes to the ferry terminals, or specific destinations like the Atheneum, I had no idea what hidden treasures (or scary surprises, in the form of invasive weeds) might be hidden in the cobblestoned back streets or “in between” spaces of Town. Old gardens that have not been intensively landscaped are something of a snapshot of gardens past, and ignored “in between” spots like medians or overgrown lots can be a catch-all of native and introduced “weedy” species.
From early September through early November, whenever I had an hour or two available for exploring, I began surveying the streets on foot and making note of any unusual finds. In about 10 visits of 1-2 hours walking each visit, I was able to cover most of the downtown area. While I did find some more “garden escapes” that are not native to New England or North America, as expected, I also encountered a couple interesting mystery plants that are native to the Northeast but never before recorded or vouchered on Nantucket. It’s unclear how these plants arrived on island, or how long they’ve been here. Many early botanists did spend a lot of time collecting downtown, so it seems unlikely that these species were present on the island all along flying under the radar. Early botanists were trying to “collect them all” with the fervor of Pokemon Go! players. And they included some of the best botanists in the country, like E.P. Bicknell who visited the island for a number of consecutive seasons (1908-1919) and named and described species that had gone unnoticed for many years. Bicknell and skilled local botanists worked hard to prepare comprehensive species lists, and many of their early pressed specimens (vouchers) may be found today in the Maria Mitchell Association’s herbarium collection, which houses more than 4,500 plant specimens, mainly from the island.
The most dramatic find this summer was tall snakeroot (Ageratina altissima), a late-season bloomer in the Aster Family. I first encountered it in a waste area on a wooded slope edging the parking lot behind the First Congregational Church, and later found it growing “wild” in the street edges and in some minimally groomed yards around Academy Hill and a couple other locations offering partial shade and a laissez faire attitude to gardening. This showy wildflower is native to the eastern half of the country, including Cape Cod and Martha’s Vineyard. Considered unwelcome in agricultural areas, its foliage and roots are highly toxic, and the toxins are passed on through the milk of livestock grazed on it, causing “milk sickness” which killed many early European settlers. Somehow the lacy white late-summer flowers of tall snakeroot have found a home in Town’s shady gardens, possibly brought to the island intentionally for garden use or as a hitchhiker with other garden plants.
Interestingly, a related plant, lesser snakeroot (Ageratina aromatica) has long been known to exist on Nantucket, but that fire-adapted species inhabits dry woodlands and has shorter leaf stalks than tall snakeroot, which prefers moister woods and disturbed areas. Lesser snakeroot is MA State Endangered, and Nantucket is near the northern edge of its range. It’s so rare that I have not yet encountered it in my botanical explorations, though I have visited appropriate habitats and historic sites where it has been found.
In contrast, another downtown find, three-seeded mercury (Acalypha rhomboidea) is a common weedy species, with no real ornamental value. Nondescript and found downtown growing in the leaf litter of alleyways and cobblestoned streets, this annual in the Euphorbia Family has green bracts surrounding its seed clusters, rather than sporting showy flowers. Like tall snakeroot, three-seeded mercury is native to the northeast, including the Cape and Martha’s Vineyard. I first noted this plant on Still Dock Street, but later found it to be abundant on many less-traveled cobblestoned streets, and as a weed in other yards.
Clearly this small unobtrusive plant has exploited a niche throughout the downtown area, perhaps after arriving as seeds carried in the treads of a visitor’s shoes, or in the soil of more conspicuous ornamental plants brought to the island to fill garden beds.
Have you encountered these plants elsewhere on Nantucket? It’s possible they could be in a yard or backstreet near you. As these plants are native to our eco-region and to Massachusetts, they are an interesting addition to the island’s biodiversity rather than a cause for concern. Because they’ve shared an evolutionary history with our region’s plant communities and insects, they are likely to fit in seamlessly with island ecology. Tall snakeroot, despite its toxicity to mammals, provides a late-summer feast for hungry nectaring insects, and several insects are known to feed on its foliage. In fact, leafminers were abundant on our downtown plants, and a quick email to Charley Eiseman, who has been studying leafminers and gall insects on Nantucket through Nantucket Biodiversity Initiative grants for almost a decade, said that they would be a new species for the Nantucket insect list. It’s interesting to wonder if this plant and its leafminer associates have been here all along or were introduced at some point in the recent past as a package deal!
Finding “new” plants and insects like this enhances our understanding of local ecology and aids us in protecting Nantucket’s natural world. Curious about the plants in your neighborhood, or think you’ve seen a plant that’s a recent washashore? Get in touch with me here at NCF, by contacting me via email, email@example.com, and we can talk botany!