Jan., 1905.] Mat Plaids. 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 fleshv. 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 tvpical 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, of 

 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 svnonvmouslv, 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 dactyloides (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 extensively on newly plowed land. On 

 newly broken prairie thev 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, 



