While Nantucket can’t usually lay claim to epic snowfalls and frigid temperatures, the colder months bring a chilly dormancy to most plants. Rather than expose their leaves to the freezing temperatures and desiccating salty winds, most of our plants and trees shed their leaves. Conifers such as pitch and Japanese pine, and red cedar with its blue fruit, retain their green colors at least to some extent as they do not shed their needles in the fall. Red cedar often turns a dingy maroon-tinged color before greening its needles up again in the spring, and American holly retains its glossy forest-green leaves, but most other species are dressed in shades of grays and browns and reduced to stems and branches.
While winter’s exposed tree trunks and tangled shrubs and vines can be grim and forbidding, they give us the opportunity to focus on some tiny species that remain green throughout the winter but often go unnoticed the rest of the year. A lesser-known evergreen on Nantucket is the ground-pine or blue ground-cedar (Diphasiastrum tristachyum), which is actually a club moss and not tree or shrub at all. Ancient club mosses of the Carboniferous era (300-350 billion years ago) grew to the stature of trees and when they died off, they were transformed into coal deposits. Today’s club mosses are quite small, and many resemble the blue ground-cedar and Hickey’s tree club moss (Dendrolycopodium hickeyi), another species native to Nantucket. Once considered members of a single genus, Lycopodium, recent genetic study has led botanists to re-classify these interesting plants into several different genera. Check out the different forms and family ties of the various Lycopodiaceae in this article and learn more about how they grow.
These miniature tree-like plants have grown very scarce here on island though they remain common in many New England woodlands. Winter is the best time to search for them, as their green colors are vibrant and strong against the neutral background, and you can see through the leafless brush.
In working on the Nantucket Flora Update, I have been seeking these “little green guys” for several years with little luck, only finding a single patch of Hickey’s tree club moss near Stump Pond, and not encountering any of the ground-cedar until last week, when our new CEO, Cormac Collier, mentioned that he had found some unusual plants on a walk at Madequecham Valley. A visit to the area he described revealed several diminutive clusters of these tree-like plants, barely visible among dense huckleberry and Pennsylvania sedge, and growing along a deer path. I had searched adjacent areas in past seasons but missing by a few meters is as good as missing by a mile when you are looking for tiny cryptic plants!
It’s not completely clear why these club mosses have dwindled in numbers here on Nantucket and can no longer easily be relocated at their historic sites. Club mosses’ short stature may make them vulnerable to being overgrown and shaded out by tall shrubs. However, off island they are commonly found in patches on the forest floor in pine and mixed forests, so you might imagine that they’d take advantage of the island’s expanding pitch pine forests.
But if they are not vigorous enough to produce strobili (cones) they will not be able to spread to new areas naturally via wind-blown spores. The tiny scattered ground-cedar clumps I observed at Madequecham were all very stunted and all lacked strobili, likely due to the harsh south shore environment–think salt spray and wind, and strong competition from aggressively growing huckleberry and scrub oaks. With open pitch pine forest nearby, they have a chance to colonize a new habitat, but they will need to disperse farther than the creeping of their horizontal rhizomes will allow!
The fact that club mosses’ numbers have dropped so low also makes it more difficult for them to exploit newly available habitat. It’s possible that these slow-growing club mosses were over-harvested for Christmas decorations in years past. Where I grew up in New Hampshire, there were at least four different species of club mosses growing in the woods behind my parents’ house, and they were so abundant that a little collecting of individual stems did not make much of a dent in the widespread populations. Hemlock, white pine, and spruce boughs could also be used to decorate and were plentiful in my hometown. Here on Nantucket, however, club mosses were probably always less numerous and only grew in limited locales. With few holiday foliage alternatives, too much may have been removed each season. Pulling on a single stem of ground-cedar can uproot an entire long rhizome, decimating a population in just a few years. A small section of club moss represents several years of slow growth, rather than a year or two of branch tip growth you might cut from a spruce, cedar, or fir!
Interestingly, the patch of Hickey’s tree club moss, sometimes also called “princess pine” near Stump Pond is in on a steep and densely shrub-covered slope, which tends to protect it from foot traffic and may make it harder for deer to access. This patch has been expanding over the past few years, and is producing strobili, but I was not able to locate any other patches of the plant nearby at Stump Pond or elsewhere on the island. While deer are not known to be particularly fold of club mosses, desperate over-browsing by deer during harsh winters may have also played a role in club mosses’ Nantucket decline.
If you are out and about hiking on island conservation trails, remember that these “little green guys” are busy photosynthesizing while the overstory trees and encroaching shrubs are leafless, and plenty of sunlight reaches the ground level. While these small tree-like plants are only a tiny piece of Nantucket’s ecosystems, losing a few species here and there over time on our island at sea is a blow to our total biodiversity. So, please give the “little green guys” a break and help protect them by letting them be. And stay tuned– it’s possible that we may be able to give these species a “lift” to help them colonize new habitat with more suitable present-day conditions. In researching this option, I came across information that suggests we should be able to propagate them from spores or from root cuttings to give them a new lease on life. Check out some info on propagating these little guys.
If you do find some interesting club mosses around the island, please send me the location (coordinates are ideal) and a picture if possible, so they can be documented in the Nantucket Flora update and measures can be taken to protect them for the future.