Floristic studies of introduced and native seaweed populations from 14 open coastal and estuarine sites within southern Maine and New Hampshire were documented between 1965 and 2017. A total of 186 seaweed taxa were recorded, including 15 introduced (8.1%) and 171 native (91.9%) species. The highest species diversity (123 taxa) occurred at the open coastal Seapoint Beach site in Kittery, Maine, and an estuarine tidal rapid site at Dover Point, New Hampshire, with 106 taxa. The numbers of introduced species per site ranged from 2–11. The percent occurrence patterns for the 15 introduced seaweeds were highly variable, with Codium fragile subsp. fragile and Ulonema rhizophorum being restricted to single sites (7%), Melanothamnus harveyi occurring at 12 sites (86%), and Agarophyton vermiculophyllum and Dasysiphonia japonica at 13 sites (93%). The geographical origins and initial collection dates for the 15 introduced taxa were highly variable, with their initial collections ranging from 1848 (M. harveyi) to 2007 (D. japonica). Codium fragile subsp. fragile had the most protracted period between its initial occurrence at Orient Point, New York, in 1957 and in northern New England 40 years later (i.e., 1997). By contrast, several other introduced taxa had rapid geographic expansions within five years. The numbers and abundance of introduced species in the Gulf of Maine have increased dramatically between 1986 and 2017, with nine recorded in 1986 and 15 in 2017. Two native warm-water red algae (Agardhiella subulata and Gelidium crinale) showed sudden northward expansions during 2016 and 2017, respectively. Their presence may be associated with global warming, which is presently occurring at an alarming rate within the Gulf of Maine and exceeds many areas within the world.

Coastal erosion at Stonewall Beach on the island of Martha's Vineyard, Massachusetts, U.S.A., has exposed a thick layer of peaty sediments rich in botanical remains, including well-preserved tree trunks. We identified the species of the tree trunks based on wood anatomy, analyzed pollen and macrofossils in the sediments, and determined the ages of the tree trunks and peat with ¹⁴C dating. The tree trunks were identified as Pinus strobus (white pine), and pollen assemblages featured high percentages of P. strobus in sediments associated with the trunks. The tree trunks and peat dated to ∼10,700–9800 calibrated ¹⁴C years before present. These findings confirm that Martha's Vineyard, like other parts of southern New England, was dominated by P. strobus forest during the early Holocene. At that time, regional climate was drier than today and Martha's Vineyard was not yet isolated from the mainland by postglacial sea-level rise.

Euphorbia ipecacuanhae L. is an herbaceous perennial of disturbed, sandy habitats of the Atlantic coastal plain, ranging from Georgia to southern New England. Most references list Hartford County, Connecticut, as the northernmost station and the only New England record for the species. However, we recently encountered a putative record from Nantucket, Massachusetts, U.S.A., and investigated its validity. Using a combination of physical inspection of the specimen and biographical details of the collector, Lorin Low Dame, we conclude that E. ipecacuanhae was collected from the island of Nantucket in the late 19th century, expanding the known natural range for the species. We also discuss habitat and landscape-scale ecological processes that would have supported the species at that time and prospects for its rediscovery in New England.