Annotated List of the Plants Growing Naturally 

 at the National Arboretum 



Oliver M. Freeman' 



An understanding of why plants native to the eastern United States are 

 now either abundant, rare, or absent at the National Arboretum depends on a 

 knowledge of the soils, moisture, drainage, and general land usage previous to 

 and after purchase of the Arboretum tract by the Federal Government in 1927. 



Before 1927 about half of the 420-acre area was used for field crops and 

 truck gardens. This brought in the usual weeds associated with such activities. 

 Before erection of a fence in 1934 and 1935, the wooded areas were burned 

 over nearly every year, destroying much of the leafmold that is required by 

 many of the choicest plants. The need for leafmold is especially noticeable 

 with rattlesnake-plantain, Goodyera pubescens, which was undoubtedly abun- 

 dant many years ago. Only one plant of this little orchid was found in 1949. 



Many of the original colonies of native plants have been destroyed by 

 encroachment of Japanese honeysuckle, Lonicera japonica. Erosion of culti- 

 vated and other disturbed soil has undoubtedly changed the flora in small 

 areas. Also, some changes are being made each year by road construction, 

 grading, and landscaping. 



The area is composed of rolling land with relatively few level fields between 

 the higher elevations. The southwestern part of the grounds is dominated 

 by Mount Hamilton (alt. 239 feet), most of which is covered with the original 

 trees. The east-central part is dominated by Hickey Hill, which overlooks the 

 Anacostia River. Hickey Run flows through the center from a northwesterly 

 to a southeasterly direction, forming a broad valley between the two elevations 

 named above. 



Soils range from sandy loam to heavy clay. There are several small areas 

 of gravel and others of ironstone concretions. Layers of sand, gravel, and 

 ironstone resting on clay have given rise to numerous springs, hillside seep- 

 ages, and swamps, providing suitable spots for plants requiring wet soil. 

 Along the eastern edge of the area is the Anacostia River with its steep 

 wooded banks and tidewater plant associations at their bases. These areas of 

 wet soil have developed a flora quite distinct from that found in the normal 

 woodlands. The soil reactions range from neutral to slightly acid, becoming 

 very acid in the leafmold deposits associated with mountain-laurel. 



The plants listed are those known to be growing naturally as of this date 

 within the fenced boundaries of the Arboretum or upon the narrow strip of 

 alluvial flats between the unfenced eastern boundary and the stone wall along 

 the Anacostia River from Hickey Run to the Licking Banks Spring. 



This list includes the plants reported in unpublished lists prepared in 1918 

 by Ivar Tidestrom and in 1934 and following years by E. C. Leonard, except 



5 Retired. 



