1919] Fernald,— Arenaria 8 
which is separated by others because it has “a conspicuous 10-lobed 
and glandular slightly perigynous disk." Again Pax defines Alsine 
(including Ammodenia) as having a l-celled ovary, while Merckia 
is distinguished by its 3-5-celled ovary; yet Gray, in his Genera, 
described (correctly) the ovary of Ammodenia as 3-5-celled. The 
tabulation on the opposite page, however, presents the significant 
characters most relied upon in the separation of these five genera. 
When these so-called differential characters are checked by exam- 
ining species from remote areas of the world we get the following 
results. 
Most species of Arenaria (in the strict sense) and of Minuartia 
have a tufted habit, with terminal inflorescences and numerous reni- 
form seeds. But the common A. lanuginosa (Michx.) Rohrb. of 
South America, Mexico and the southern United States has elongated 
stems with broad leaves and axillary pedicels, thus in habit strongly 
simulating the European Moehringia trinervia (L.) Clairv. The 
latter plant, on account of its habit and its lustrous strophiolate 
seeds, is unquestionably a species of Moehringia. Yet the seeds of 
Arenaria lanuginosa, a plant which in habit belongs to Mochringia, 
are quite like those of M. trinervia in form and lustre, but they lack 
the strophiole; i. e. only by its lack of a strophiole does Arenaria 
lanuginosa find a place in Arenaria, not in the habitally similar 
Moehringia. 
Between Arenaria proper and Minuartia the only distinction is in 
the valves of the capsule, cleft in Arenaria, entire in Minuartia, the 
species of these so-called genera otherwise so closely simulating one 
another as to be often nearly inseparable. "Thus, Arenaria paludicola 
Robinson, which has the entire valves of Minuartia, is habitally 
close to A. lanuginosa, a true Arenaria, and to species of M oehringia. 
Furthermore, it is by no means easy to determine whether some of 
our American species belong with Arenaria or with Minuartia, some 
species having the valves so slightly cleft that in their capsules they 
lie between the most characteristic species of the two groups. Thus 
A. sajanensis and the species related to it (and discussed below, pp. 
12-17) have emarginate valves as does A. laricifolia of Europe, 
beautifully illustrated by Reichenbach (Ic. Fl. Germ. v. t. 292, fig. 
4933) with notched valves, although these plants are universally 
placed in the so-called genus which is distinguished by having entire 
valves! 
