Border Species of Texas 
Caesalpinia mexicana, Mexican poinciana 
Citharexylum berlandieri, Berlandier fiddlewood 
Cordia boissieri, anacahuita 
Cercidium macrum, border paloverde 
Ehretia anacua, anaqua 
Esenbeckia berlandieri, Berlandier esenbeckia (extinct in 
U.S. except in cultivation) 
Fraxinus greggii, Gregg ash 
Leucaena pulverulenta, great leadtree 
Pistacia texana, Vexas pistache 
Pithecellobium flexicaule, ebony blackbead 
Pithecellobium pallens, huajillo 
Quercus gravesii, Graves oak 
Sabal mexicana, Mexican palmetto 
Yucca carnerosana, Carneros yucca 
Yucca faxoniana, Faxon yucca 
Yucca rostrata, beaked yucca 
Border Species of Southeastern Arizona 
(mostly within Coronado National Forest) 
Arbutus arizonica, Arizona madrone 
Erythrina flabelliformis, southwestern coralbean 
Eysenhardtia polystachya, kidneywood 
Fraxinus papillosa, Chihuahua ash 
Quercus hypoleucoides, silverleaf oak 
Quercus oblongifolia, Mexican blue oak 
Quercus rugosa, netleaf oak 
Quercus toumeyi, Toumey oak 
Salix bonplandiana, Bonpland willow 
Salix taxifolia, yewleaf willow 
V auquelinia californica, Torrey vauquelinia 
Yucca schottii, Schotts yucca 
Border Species of Southwestern Arizona Deserts 
Bursera fagaroides, fragrant bursera 
Bursera microphylla, elephanttree 
Forestiera phillyreoides, desert-olive forestiera 
Parkinsonia aculeata, Jerusalem-thorn 
Quercus ajoensis, Ajo oak 
Sapium biloculare, jumping-bean sapium 
APPLICATIONS OF THE MAPS 
Several applications of these maps of minor western hard- 
woods may be repeated from Volume 1, though most uses are 
obvious. First, the maps show where each tree species grows 
wild and can be found for study for any purposes. Also, where 
plantations or trees from locally collected seed should be 
successful. 
To specialists, the maps may reveal errors and suggest 
corrections, also likely localities where further field work is 
needed for revision and where range extensions and State 
records may be sought. The natural ranges are preserved for the 
historical record, before the forests are destroyed or partly 
replaced by plantations of improved varieties and hybrids. The 
maps have economic value, suggesting possible sources of wood 
and other products in addition to the detailed information on 
timber volumes provided by forest surveys. 
The transparent overlays (Volume 1) and maps together 
summarize graphically the average and extreme conditions of 
the environment (temperature, precipitation, latitude, altitude, 
etc.) of each species. They provide the basis for correlation 
studies of distribution of a species and the environment, 
including limiting factors. Also, these*maps may indicate local 
climates to which geographical or local races may be adapted. 
The maps are of special importance in the collection of seed. 
They show first the geographic areas and localities where seed 
can be collected from wild trees. They suggest the possible 
occurrence of geographic races and seed sources, particularly 
for tree improvement programs including hybridization tests and 
for testing or introduction beyond the native range, such as 
foreign countries with similar climates. 
Maps can be helpful in identifying wild trees, indicating the 
presence or absence of a species in a particular area. For tree 
identification a new handbook with revised small maps is 
planned. 
Finally, the maps serve as background material for such 
studies as classification, evolution, paleobotany, and genetics. 
Also, the distribution of associated animals and plants, particu- 
larly insects and parasitic fungi. 
FUTURE WORK 
A revised Atlas with highly accurate maps of the native tree 
species of continental United States could be compiled at an 
early date after additional field work in many places. Future 
human activities may affect tree distribution and obscure the 
natural ranges. Some forests are being removed by cultivation 
and other land-uses, while others will be replaced by plantations 
of improved tree varieties and hybrids. A few species may 
become extinct at outlying stations or be restricted by insect 
pests or diseases. Others may migrate and shift their ranges in 
response to climatic cycles and other factors. Thus, these maps 
showing natural ranges at present may have additional, histori- 
cal significance in the future. 
Unpublished notes and publications on tree distribution, 
including range extensions and corrections, will be welcome at 
any time. Such material may be addressed to the Dendrologist, 
USDA Forest Service, Washington, D.C. 20250. 
There is still a need for more articles, bulletins, and books 
devoted to distribution maps of native tree species prepared by 
experienced resident botanists or foresters in those States not 
already covered by references. 
Botanists and foresters are urged to publish promptly articles 
containing records on range extensions of trees from their 
collections, herbaria, or observations. Duplicate specimens 
confirming these records should be deposited in one or more 
large herbaria, as well as in the State or institution herbarium. 
Care should be taken in all distribution records including maps 
and herbarium labels to distinguish between wild trees appar- 
ently native and trees introduced into the locality directly or 
indirectly by persons, whether planted, escaped, adventive, or 
naturalized. 
SUMMARY 
“Minor Western Hardwoods” is the third volume of an Atlas 
showing the natural distribution or range of the native tree 
species of continental United States. This volume contains large 
maps of 210 tree species native in western contiguous (or 
conterminous) United States and not among the 34 important 
western hardwoods in Volume 1. 
