Jan., 1905.] 
Mat Plants. 
265 
MAT PLANTS. 
John H. Schaffner. 
Mat plants are plants with numerous prostrate branches 
which are usually closely crowded and form a more or less circular 
body a few inches to eight or more feet in diameter. This pros- 
trate discoid body habit is quite characteristic of a small number 
of plants belonging to various families. Among the most typical 
mats may be mentioned Amaranthus blitoides Wats., Portulaca 
oleracea L., Euphorbia maculata L. and Euphorbia serpyllifolia 
Pers. Mats are usually annual plants either of the ordinary her- 
baceous type or very fleshy. There are. however, a number of 
geophilous perennials which form mats, like Verbena bracteosa 
Mx. The main radiating branches usually give rise to numerous 
smaller branches and they may or may not strike root. In the 
more typical cases there are no roots except the main central 
root. Mats are especially characterized by having a large num- 
ber of small leaves, seeds, and flowers. These peculiarities, cf 
course, harmonize with the shape and position of the plant. 
Like most ecological groups, mat plants intergrade with other 
types of body habit. On the one hand they pass over into such 
forms as Malva rotundifolia L., Callirrhoe involucrata (T. and G.) 
Gr., Citrullus citrulus (L.) Karst., and the typical carpet plants; 
and on the other, transitions occur between them and tumble- 
weeds or even normally erect forms. Although it is not intended 
to give a definition here of carpet plants, yet, since the terms mat 
and carpet are often used synonymously, it might be stated that 
typical carpets are perennials with numerous trailing branches or 
runners which take root at the nodes and develop low tufts of 
leaves or rosettes, finally forming a close low covering of the 
ground. Among this type of carpet plants may be mentioned 
the buffalo-grass, Bulbilis dactvloides (Nutt.) Raf., and the 
various species of Antennaria. 
Mat plants are at home in open and exposed places where 
there is little or no individual crowding. They are abundant on 
prairies and appear extensivelv on newly plowed land. On 
newly broken prairie they are usually the most characteristic 
vegetation. They are also prominent on dry or moist sandbars, 
on salt marshes, and in cultivated fields. 
Nearly all typical mats, when growing in shaded places, 
assume the upright habit. But it is especially interesting to note 
that normally erect plants may assume the mat habit in a suitable 
environment. One of the most striking cases is the slender pig- 
weed, Amaranthus hybridus L., which is usually erect and often 
attains the height of eleven feet. This plant when growing on 
exposed dry or moist sandbars frequently develops as a mat, 
