I guess I had never visited the dunes of the Atlantic coast in September before, because I was surprised to discover the seaside goldenrod (Solidago sempervirens) growing amid the beach grass (Ammophila breviligulata) on South Beach, Martha’s Vineyard last weekend. It is an odd-looking goldenrod; most Solidago species have toothed leaves, usually with rough surfaces, and the individual flowers are tiny. Seaside goldenrod flowers are larger than those of other members of the genus and the leaves and stems are fleshier and thicker, an adaptation to living in a salty, windy environment, where preservation of water is important.
Coastal beaches on Martha’s Vineyard consist of un-vegetated beach faces and berms, sparsely vegetated foredunes dominated by American beach grass and seaside goldenrod and more stabilized and densely vegetated inner dunes with bayberry, saltspray rose (Rosa rugosa), poison ivy (Toxicodendron radicans) and winged sumac (Rhus copallina).
S. sempervirens gets its trivial name (“always green”) from its habit of holding on to its leaves through much of the winter and sprouting new ones in February or March. They are red when they emerge and then turn green. It begins flowering in August, along with the other goldenrods, but keeps flowering into November, after the other goldenrods have been felled by frost. Seaside goldenrod can be from 3 to 6 feet tall (some sources say up to 8 or 10 feet all); it is shorter in more exposed and nutrient starved locations and taller elsewhere.
There are two subspecies. S. sempervirens var. sempervirens, which has showier flowers and grows south to Connecticut, and var. mexicana, which is smaller and grows from Massachusetts south to Texas. It also hybridizes regularly with rough-stemmed goldenrod (S. rugosa).
It is quite salt tolerant and has spread inland in some areas, where it is confined to heavily salted roadsides. It occurs naturally not only from Newfoundland down the east coast of the United States, but also down the St. Lawrence River valley to the Great Lakes. It has spread further into to the Great Lakes region, becoming established in saline areas where few other plants are present to compete with it. It is not regarded as invasive, as it does not spread out of these marginal areas.
Because it is adapted to dune dwelling, seaside goldenrod is one of the species is that is replanted in areas where beach and dune restoration is underway. Beach grass is the primary species to be planted in these projects, but S. sempervirens, beach pea (Lathyrus japonica), beach plum (Prunus maritima), bearberry (Arctostaphylos uva-ursi) and bayberry (Myrica pensylvanica) are all planted as well.
I haven’t seen any references to a restoration of South Beach on Martha’s Vineyard and the beach grass/goldenrod community in the dunes there is likely natural. But Joseph A. Sylvia State Beach, a barrier beach between Oak Bluffs and Edgartown, on the northeast side of the island, sees more heavy use and it has been restored using dredged materials 12 times since 1997. In 2008 the Friends of Sengekontacket commissioned the Woods Hole Group to do a study of the state beach and it produced a plan that serves as a guide to managing the beach in the face of heavy use and rising sea level. In November 2012 Hurricane Sandy badly damaged the barrier beach and the sand replenishment and revegetation effort after that event was the most restoration.
In addition to growing on beaches and sand dunes in coastal areas, seaside goldenrod grows in high parts and along the edges of fresh, brackish and salt marshes. It is found in parts of the marsh that are irregularly flooded by tides. It can play an important role in providing nesting habitat for shorebirds like willets, killdeer, and black skimmers.