CONTRIBUTIONS FROM THE GRAY HERBARIUM OF 
HARVARD UNIVERSITY. 
New Series.— No. LVII. 
M. L. FERNALD. 
I. THE UNITY OF THE GENUS ARENARIA. 
Ir seems wisest to maintain the genus Arenaria in its broad sense, 
although the great majority of European authors and some in America 
distinguish from Arenaria proper (with the valves of the capsule 
notched or cleft at apex, and seeds numerous and reniform) the fol- 
lowing genera which occur in boreal America: Alsine Wahlenb. or 
Minuartia L. similar to Arenaria but with uncleft valves; Ammo- 
denia Gmel. or Honkenya Ehrh., with unusually developed disk, 
globose capsule, and few obovoid seeds; Moehringia L., with well 
developed disk and with the seeds strophiolate; and Merckia Fisch., 
with 3-5 celled ovary and inflated capsule. 
Although in a limited area, like Europe or like northeastern America, 
the lines usually indicated for the separation of these genera are 
fairly definite, an examination of species from a broad range of terri- 
tory at once shows that no two of the traditional characters are con- 
comitant throughout a long series of species 
In order to test the value of these genera or is well to tabulate the 
characters depended upon by those who maintain the segregated 
genera as distinct from Arenaria; and even in this it is difficult to 
find authors in entire agreement. Thus, some authors state that the 
seeds of the monotypic Ammodenia or Honkenya are “numerous,” 
others “few,” while Pax, in Engler’s Naturlichen Pflanzenfamilien, 
retains under Alsine with “Discusschuppen meist kurz” Ammodenia 
