232 
M. L. FERNALD 
recently demonstrated to be a unique American representative of the 
Eurasian R. maritimus, differing from the Old World plant in constant 
characters which led Philippi and Dusen to set it off as R. maritimus, 
var. fueginus. Outside its broad range in interior and western North 
America, var. fueginus is known on Tierra del Fuego and on the coast 
from Rhode Island to the Gulf of St. Lawrence, chiefly on the outer 
islands which persist as a remnant of the continental shelf: Block 
Island, Martha's Vineyard, Nantucket, Sable Island and the Magdalen 
Islands. 
Three more illustrations, and I shall have finished this long cata- 
logue. Certain genera, chiefly of the southern hemisphere, are note- 
worthy because of their restriction there to Australia or Australia and 
New Zealand and tropical South America and their occurrence north 
of tropical North America only on the Atlantic slope. Of such genera 
two examples may serve. Psilocarya (fig. i6) occurs in tropical Aus- 
tralia and tropical easterfi South America and Cuba, and is represented 
in continental North America by two extremely local species. The 
most remarkable of these is P. scirpoides, as rare a sedge as we have 
in our flora, known only from wet sands and peats of southern Massa- 
chusetts and Rhode Island, and at similar unique stations near the 
head of Lake Michigan. As our second illustration may be taken the 
genus Erechtites (fig. 19), highly developed in Australia, New Zealand, 
eastern and northern South America, Central America, tropical 
Mexico and the Antilles, and represented in eastern North America 
by the widely dispersed fire-weed, E. hieracifolia. The only other 
species of temperate North America is a unique plant, E. megalocarpa, 
of the sea-strands of southern Cape Cod, there occurring on one of the 
most ancient of habitats, the strand of the Atlantic. 
In fact the ever-shifting but ecologically uniform and never- 
changing sea-margin is largely inhabited by an extreme relic flora. 
This has already been pointed out in case of plants of Bering Sea or 
the North Pacific, occurring likewise on the strands of the Gulf of 
St. Lawrence, as well as by such plants as Polygonum acadiense on the 
seashores of Cape Breton and of the lands bordering the Baltic. This 
persistence on our coast of relics of an ancient wide dispersal in saHne 
habitats is well shown by the remarkable Junci thelassii. This unique 
section of the genus has seven living species, all of saline and subsaline 
habitats and with a distribution ''which indicates that they are rem- 
nants of an ancient group. /. acutus or one of its varieties occurs in 
