The American Midland Naturalist 
PUBLISHED BI-MONTHLY BY THE UNIVERSITY 
OF NOTRE DAME, NOTRE DAME, INDIANA. 
VOL. II. MAY, 1912. NO. 9. 
IIl.—OUR AMPHIBIOUS PERSICARIAS. 
By J. A. NIEUWLAND. 
In regard to the plants known as Amphibious Persicarias, 
Smartweeds, or Knotweeds, and especially as to the specific 
delimitations of them as a group, various opinions have at one 
time or another been suggested, but only one or two have pre- 
vailed in our modern manuals or floras. The older Gray’s manuals 
as also the manuals emanating from the New York Botanical 
Garden, such as Britton’s, and Small’s, recognize three species 
of these plants for the United States, P. amphibium Linn., P. 
emersum Michx., or P. Muhlenbergi Wats., and P. Hartwrighti. 
The new so-called Gray’s Manual, seventh edition of Fernald 
and Robinson, relegated the last-mentioned species to the rank 
of a variety, as some one has told me ‘because Massart had shown 
that P. amphibium changed into P. Hartwrightit when grown 
out of water.’ The absurdity of such a reason I have already 
pointed out in another place.* 
The very proposition of change refutes itself, and the person 
affirming it manifests botanical superficiality, and innocency, 
by failing to see the meaning of Polygonum amphibium Linn., 
failing to perceive that Linhaeus knew in Europe a Persicaria 
which existed in two phases one a floating-leaved aquatic, the 
other phase quite terrestrial, that he called the two phases one 
species, not even designating the forms and varieties, which of 
course, they are not; forms, or rather phases or even different 
parts often of the same individual plant! 
This double existence of the species has as I have pointed 
* Am. MIDLAND NATURALIST, vol. li, pp. 2 and 3. 
