MANUAL OF THE GRASSES OF THE UNITED STATES 



The conditions under which a plant 

 normally grows is its habitat. Some 

 species are narrowly restricted in their 

 habitat — being found only in sand or 

 on rocks, in salt marshes or on alpine 

 summits, for example, whereas others 

 are tolerant of wide variations of 

 habitat. Red fescue (Festuca rubra) 

 is an example of wide distribution of 

 a species tolerant of a variety of 

 habitats. It is found from the Arctic 

 regions south at low altitudes to 

 Georgia and central California and 

 in the mountains farther south, and 

 from the seacoast marshes to moun- 

 tain tops. 



Each species is found growing over 

 a rather definite geographic area, but 

 within this area it is confined to its 

 particular habitat. 



In mountain regions altitude is an 

 important factor in modifying range, 

 each species thriving within certain 

 limits of altitude. Species found at 

 high altitudes in one range of moun- 

 tains may reappear at about the 

 same altitude on other ranges. Cer- 

 tain grasses growing at low levels in 

 the north are found in the mountains 

 and at increasingly higher elevations 

 southward. 



The geographic range is of impor- 

 tance and is given in some detail for 

 each species in the manual. The 

 range as given is based upon the 

 study of a vast amount of material, 

 both in the herbarium and in the 

 field. For convenience in keeping the 

 records of distribution a series of out- 

 line maps, one for each species or 

 variety, has been prepared in the 

 grass herbarium of the United States 

 National Herbarium. The known 

 range of each species is indicated 

 upon these maps by a dot on each 

 State from which specimens are in 

 the herbarium or have been examined 

 by the author. (A few extensions of 

 range have been found since the 

 maps were engraved. These are in- 

 cluded in the text.) Local floras, lists, 

 and records of distribution have been 

 checked, and efforts have been made 

 to verify the records that seemed to 

 indicate an extension of range. Other 



herbaria have been visited or have 

 lent specimens, and many correspond- 

 ents have submitted specimens for 

 verification. No additions have been 

 made without a study of the speci- 

 mens. But it must be borne in mind 

 that dots (representing specimens) 

 necessarily indicate where the differ- 

 ent specimens have been collected, 

 therefore where botanists have been. 

 Absence of a dot in a state does not 

 necessarily mean the species in ques- 

 tion does not grow in that state. 



The ranges of native species are 

 usually fairly well defined and con- 

 tinuous. A species of the Coastal 

 Plain extends, for example, from New 

 Jersey to North Carolina or from 

 Virginia to Florida and Texas, with- 

 out a conspicuous break. Mountain 

 plants extend along mountain ranges 

 where similar conditions prevail. Some 

 species have in the main a continuous 

 range but are found also in isolated 

 and distant localities. Bouteloua hir- 

 suta extends over the Great Plains 

 east to Wisconsin and Louisiana, and 

 again occurs abundantly and ap- 

 parently native on Sanibel Island, 

 Fla. Some Coastal Plain species ap- 

 pear again around the head of Lake 

 Michigan. In these cases it is prob- 

 able that the species do not occur in 

 the intermediate areas. 



Certain arctic or northern species 

 also show interrupted range, being 

 found within the limits of the United 

 States only on isolated mountain 

 tops. The arctic grass, Phippsia 

 algida, for example, is known within 

 the United States only from alpine 

 summits in Colorado. What appear 

 to be interrupted ranges along the 

 northern or southern borders are 

 mostly due to extensions into this 

 country from the main ranges in 

 Canada or Mexico. 



The distribution of recently intro- 

 duced species is often very erratic. 

 A single introduction may maintain 

 itself or even spread considerably 

 for several years before coming to 

 the notice of botanists. Introduced 

 species often travel rapidly along 

 railroads by means of cattle cars, or 



