Natural History of District of Columbia — McAtee 69 



Myrica carolinensis Ilex laevigata 

 Quercus digitata decidua 



pliellos Hibiscus moscheutos 



lyrata Opuntia opuntia 



michauxiana Aralia spinosa 



prinoides Leucothoe racemosa 



Phoradendron flavescens Pieris mariana 



Drosera spp. Monarda punctata 



Liquidambar styraciflua Tecoma radicans 



Clitoria mariana Baccharis halimifolia 



Ilex opaca Arnica nudicaulis 



To put in another way the facts of plant distribution with 

 reference to the Fall Line, it is evident that plants which 

 prefer the higher elevations, that can exist only upon rock 

 outcrops (including such well-known controllers of vegeta- 

 tion as limestone and serpentine), or in the vicinity of water- 

 falls, or that thrive best in deep humus, loams and clays, are 

 chiefly restricted to the Piedmont. On the other hand, plants 

 of the beaches, salt marshes, tide flats, pine barrens, and 

 magnolia bogs and those that prefer lower elevations and 

 such soils as sand and sandy loams are found almost exclu- 

 sively in the Coastal Plain. 41 



In general the conditions tend to restrict most of the 

 aquatic and semi-aquatic groups to the Coastal Plain. Thus 

 this province has the lion's share of Potamogeton, Sagittaria, 

 and of grasses and sedges in general, although such large 

 genera as Panic inn and Carex are more evenly divided. A 

 number of other genera, as Quercus, Meibomia, Eupatorium, 

 and Solidago also are about halved by the two regions. How- 

 ever, some groups show a distinct preference for the Pied- 

 mont, including the ferns, Ranunculaceae, Berberidaceae, 

 Arabis, Saxifragaceae and Araliaceae. On the whole the 

 series of plants which produce the early spring show of 

 flowers pertain to the Piedmont rather than to the Coastal 



41 Some interesting pairs of species may be cited as indicating the diverse 

 conditions on the Piedmont and Coastal Plain as possible factors in speci- 

 ation. They are (the Piedmont form in each pair being cited first) : 

 Uniola latifolia, U. laxa ; Tofieldia glutinosa, T. racemosa ; Iris cristata. 

 I verna ; Lathy rus venosus L. palustris ; Stylosanthes biflora, S. riparla; 

 Aralia racemosa, A. spinosa; Steironema hybridum, S. lanceolatum ; Vibur- 

 num cassinoides, V. nudum ; Helianthus divaricatus, H. mollis ; and Senecio 

 aureus and S. tomentosus. 



