350 MACKENZIE: Notes ON CAREX—XIII 
Gulf States west to Texas, and it also occurs around the Great 
Lakes and very locally in other parts of the interior in suitable 
habitats. It is best developed on the coastal plain but has 
pushed its way inland and is found at times on dry hills. It is 
marked by having perigynia strongly many-ribbed both dorsally 
and ventrally, and the perigynia are also slightly convex ven- 
trally and have slightly elevated margins. The ligule is usually 
very short, and the leaves are often markedly roughened above. 
The plant described by Boott as Carex Muhlenbergii var. 
enervis, on the other hand, is a species of dry hillsides, and is 
best developed in the calcareous regions of the interior. In it 
the perigynia are nerveless ventrally or obsoletely nerved at 
the base, and are much less prominently and much fewer ribbed 
dorsally. The perigynia also are not convex ventrally and the 
margins are not elevated at the base. The perigynia also aver- 
age smaller and narrower than do those of Carex Muhlenbergit; 
the ligule is more pronounced, and the leaves tend to be smoother 
above. Growing in much richer soil than Carex Muhlenbergit 
it is a strong, vigorous plant, and the starved and stunted ap- 
pearance, which one learns to associate with Carex Muhlenbergti, 
is entirely wanting. 
The Mexican Carex xalapensis Kunth, to which the plant of 
the United States has been referred, is a very similar species, 
but in it the scales are tinged with reddish- or yellowish-brown, 
the teeth of the beaks of the perigynia are less spreading, and the 
beaks are reddish-brown tinged; the perigynia are inconspicu- 
ously nerved dorsally, and the leaf-blades are much more smooth. 
It would seem best to treat a plant as well characterized as 
the above and with such a marked difference in range as a species, 
as follows: 
~ Carex plana Mackenzie, sp. nov. 
Carex pls Schkuhr var. enervis Boott, Ill. Car. 3: 124, 
pl. 400. 1862. Type from Highlands, New York; not 
C. enervis C. A. Meyer, 1833. 
Carex Muhlenbergii var. xalapensis Britton, in Britton & Brown, 
Ill. Fl. 1: 349. 1896 (as to plant described only). 
Cespitose from lignescent short-prolonged dark fibrillose root- 
stocks, the culms 3-9 dm. high, slender, but stiff, sharply tri- 
cosines rough above, leafy on lower fifth, much exceeding the 
