conspicuous, and relatively few in number of native species, being less than one-twentieth of the seed plant species. The ranges of all species of native trees, rare as well as common, have been compiled and recorded in Forest Service checklists. Now, the 6-volume Atlas of United States Trees (58, 61, 63, 65, 68, 134) previously cited has published a distribution map of each rare or local tree species. Thus, a list of tree species of small or local distribution is readily extracted from this Checklist and the Atlas.

As authorized by the Endangered Species Act, the Smithsonian Institution (112) published a report containing a preliminary list of proposed endangered and threatened plants in continental United States. This list of more than 2,000 species and varieties has since been revised (3). The Act provided that the Secretary of the U.S. Department of the Interior must study the preliminary lists and determine whether any species should be classified officially as endangered. To date, only a few plant species have been officially designated. However, a list of 1,700 vascular plant taxa (United States including Hawaii) proposed for endangered status has been published (124).

From the Smithsonian report a list of trees for continental United States was extracted (59). Trees proposed as endangered totaled 15 species and 3 varieties; those as threatened, 13 species and 9 varieties. Two were cited as extinct, but one was afterwards rediscovered and the other was extinct except in cultivation.

Lists of rare trees are somewhat broader and include many species neither endangered nor threatened with extinction. A rare species has small numbers of individuals throughout its range, which may be restricted or widespread. A local species has a relatively small range but is sufficiently common not to be called rare. Many common species are rare near the borders of their natural ranges and may be classed on some State lists as rare. Others rare along the borders of continental United States, such as tropical trees of South Florida, may be abundant beyond in nearby countries.

These reports on rare and local trees of the United States have been published (60, 62, 64). Of the 96 species of conifers native in continental United States, about 35 may be classed as rare or local in distribution. About 80 species of temperate hardwoods may be cited similarly. In addition, approximately 60 of about 98 species of native tropical trees in southern and central Florida are classed as rare there, though present in greater numbers beyond in the West Indies.

Many of these rare and local tree species occur within National Forests, National Parks, similar public areas, and privately owned preserves. Thus, the trees have some protection and are accessible for study.

ACKNOWLEDGMENTS

Grateful acknowledgment is due the Forest Service Tree and Range Plant Name Committee, which has sponsored this Checklist revision and has approved the common names. Membership (1978) is listed on the back of title page.

Other persons in the Forest Service have assisted in various ways. Two research foresters, William F. Johnston, North Central Forest Experiment Station, Grand Rapids, Minn., and Philip M. McDonald, Pacific Southwest Forest and Range Experiment Station, Redding, Calif., reviewed and updated the common names for vote by the Committee. Barbara H. Honkala, research botanist, assisted on several parts of the revision, especially in bibliographic searches, compiling citations, and

preparing the index of common names. Mary H. Devine aided in copying data.

Appendix 5, Common Names for Lumber, was revised by Robert L. Ethington and Harold E. Wahlgren, director and forest products specialist, respectively, of the Forest Products and Engineering Research staff.

Special mention is due the late William A. Dayton, director of the former Division of Dendrology and Range Forage Investigations, Forest Service, for his leadership, guidance, and valuable assistance during preparation of the 1953 checklist. As chairman of the Forest Service Tree and Range Plant Name Committee, he directed the thorough review and revision of common names in that edition. As a result, relatively few changes were needed in this revision. Also, his detailed notes on derivations of scientific names, particularly those from Greek, were a significant contribution.

Much credit is due the National Agricultural Library, of the U.S. Department of Agriculture, Beltsville, Md., and its staff, especially in the preparation of the 1953 checklist. Its Bibliography of Agriculture, published monthly, has been a valuable tool. Also, assistance was given by the Smithsonian Institution Library, including its Botany Library, in Washington, D.C. Index Nominum Genericorum was consulted for citations of accepted generic names. Its office at the Smithsonian Institution made available the latest printouts.

Various persons have contributed information on shrubby species sometimes attaining tree size and on introduced species that may be naturalized.

Ranges were copied, with slight revision, from the 6-volume Atlas of United States Trees. Thus, credit is due numerous persons for their contributions to that reference, especially curators of herbaria and authors of publications with distribution information.

Finally, because the Checklist is a compilation, grateful acknowledgment is due the authors of numerous publications on trees and other seed plants of the United States for the information assembled here. Many of these publications are mentioned under References and citations.

SUMMARY

The revised Checklist compiles the accepted scientific names and current synonyms, approved common names and others in use, and the geographic ranges of the native and naturalized trees of the United States of America (continental, including Alaska but not Hawaii). The fourth in a series, this Checklist is the official standard for tree names in the Forest Service. The Forest Service Tree and Range Plant Name Committee has sponsored this revision.

Native trees of continental United States accepted in this Checklist total approximately 679 species in 216 genera and 73 plant families. Naturalized trees add 69 species, 28 genera, and 3 families. The combined total is approximately 748 species in 244 genera and 76 plant families. Actually, the number of important native trees is somewhat less. The genus Crataegus hawthorn, has been reduced from 150 species to 35 in this revision. About 98 species are tropical trees confined in the United States to southern and central Florida. Shrubby species sometimes reaching tree size are also included. The number of varieties accepted is 49, not counting 35 typical varieties.

About 35 species of conifers native in continental United States and 80 of temperate hardwoods are rare or local in distribution. Approximately 60 of about 98 species of tropical trees in southern and central Florida are classed as rare, though present in greater numbers beyond in the West Indies.

This revision follows the plan of the 1953 checklist by the same compiler, with minor changes. Genera, species, and important varieties are listed alphabetically by accepted scientific name. Ñatural interspecific hybrids are indicated by names of parent species, with binomials added in parentheses. Pronunciation of accepted scientific names is indicated by accents. Citations are given for accepted names and commonly used synonyms. Under each genus of native trees is a summary of the approximate number of species in the world and their geographic distribution. The range of each species has been compiled from the recently completed 6-volume Atlas of United States Trees.

Eight Appendixes are: I, Condensed Checklist-Alphabetical by Scientific Names; 2, Condensed Checklist-Alphabetical by Common Names; 3, New Scientific Names of United States Trees, 1951-1977; 4, Authors of Accepted Scientific Names; 5, Commercial Names for Lumber; 6, Guiding Principles for Common Names of United States Trees; 7, Botanical Index of Plant Families and Genera; and (8) Summary of Changed Specific Names. Index of Common Names includes both those approved and others in use.

REFERENCES

Publications cited by author and number in the Introduction and Appendixes are listed in full here. Related references have been added. Titles of about 40 current descriptive floras and manuals, both regional and State, are designated by the section mark (§) and are followed by information on Crataegus, hawthorn. Numerous additional references for identification of trees and shrubs have been compiled in a separate bibliography (69).

(1) § Abrams, Le Roy, and Roxanna Stinchfield Ferris.

An illustrated flora of the Pacific States: Washington, Oregon, and California. 4 v., illus. Stanford Univ. Press, Stanford Univ. 1923-60. (Crataegus, 3 spp., 2: 473-474, illus.)

(2) American National Standards Institute.

NCPTWA word-abbreviation list. 1971 ed., 42 p. National Clearinghouse for Periodical Title Word Abbreviations, established 1966 by Standards Committee Z39. Columbus, Ohio.

1971.

(3) Ayensu, Edward S., and Robert A. De Filipps.

Endangered and threatened plants of the United States. tion and World Wildlife Fund, Inc. Washington, D.C.

(4) Bailey, L. H.

403 p.

Smithsonian Institu

1978.

The standard cyclopedia of horticulture. 6 v., 3639 p., illus. Macmillan Co., New York. 1914-17. (Reprinted in 3 v., 1925, 1961, etc.)

(5) Bailey, L. H.

How plants get their names. 181 p., illus. Macmillan Co., New York. 1933. (Reprinted 1963. Dover Publications, New York.)

(6) Bailey, Liberty Hyde, Hortorium, Staff of the.

Hortus third: a concise dictionary of plants cultivated in the United States and Canada. 1304 p., illus. Cornell University. Macmillan Publishing Co., New York. 1976.

(7) §Bailey L. H., and the staff of the Bailey Hortorium at Cornell University.

Manual of cultivated plants most commonly grown in the continental United States and Canada. rev. ed. 1116 p., illus. Macmillan Co., New York. 1949.

(8) § Barkley, T. M.

A manual of the flowering plants of Kansas. 402 p. Kansas State University Endowment Association, Manhattan, Kans. 1968. (Crataegus, 14 spp., p. 181-184.) (9) Barnhart, John Hendley, comp.

Biographical notes upon botanists. 3 v. (folio). New York Botanical Garden. G. K. Hall and Co., Boston, Mass. 1965.

(10) Boivin, Bernard.

Persoon and the subspecies.

(11) Boivin, Bernard.

Brittonia 14: 327-331. 1962.

Énumeration des plants du Canada. Provancheria No. 6. Nat. Can. 93: 253-274, 371-437, 583-646, 989-1063. 1966; 94: 131-157, 471-528, 625-655. 1967.

(12) Booth, W. E.

Flora of Montana. Part I. Conifers and Monocots. 232 p., illus. Mont. State Coll., Res. Found. 1950.

(13) Booth, W. E., and J. C. Wright.

Flora of Montana. Part II. 1959. With certain alterations and additions by W. E. Booth 1962, 1966. 305 p., illus. (maps). Mont. State Univ. 1966. (Crataegus, 4 spp., p. 111, maps.)

(14) Brayshaw, T. C.

Key to the native trees of Canada. Can. Dep. Forestry Bull. 125, 43 p., illus. Ottawa. 1960.

(15) §Britton, Nathaniel Lord, and Addison Brown.

An illustrated flora of the northern United States, Canada and the British possessions. ed. 2, 3 v., illus. Charles Scribner's Sons, New York. 1913. (Crataegus, 73 spp., by W. W. Eggleston, 2: 294–321, illus.)

(16) Britton, Nathaniel Lord, and John Adolph Shafer.

North American trees: being descriptions and illustrations of the trees growing independently of cultivation in North America, north of Mexico and the West Indies. 894 p., illus. H. Holt and Co., New York. 1908. (Crataegus, 51 spp., by W. W. Eggleston, p. 443-482, illus.)

(17) Brockman, C. Frank.

Trees of North America: a field guide to the major native and introduced species north of Mexico. 280 p., illus. (col., maps). Golden Press, New York. 1968.

(18) Browne, D. J.

The sylva Americana: or, a description of the forest trees indigenous to the United
States, practically and botanically considered. 408 p., illus. W. Hyde & Co.,
Boston. 1832.

(19) Canada, Department of Forestry.

Native trees of Canada. Bull. 61, ed. 6, 291 p., illus. (maps). Ottawa. 1961. (20) Cooper, J. G.

On the distribution of the forests and trees of North America, with notes on its physical geography. Smithson. Inst. Ann. Rep. 1858: 246-280, map. 1859.

(21) §Correll, Donovan S., and Marshall C. Johnston.

Manual of the vascular plants of Texas. 1881 p., illus. Texas Research Foundation,
Renner, Tex. 1970. (Crataegus, 33 spp., adapted from publications by E. J.
Palmer, p. 734-743.)

(22) §Cronquist, Arthur, Arthur H. Holmgren, Noel H. Holmgren, and James L. Reveal.
Intermountain flora: vascular plants of the Intermountain West, U.S.A. V. 1, 270 p.,
illus. (maps). New York Botanical Garden. Hafner Publishing Co., New York and
London. 1972.
(23) §Cronquist, Arthur, Arthur H. Holmgren, Noel H. Holmgren, James L. Reveal, and
Patricia K. Holmgren.

Intermountain flora: vascular plants of the Intermountain West, U.S.A. V. 6: the monocotyledons. 584 illus. New York Botanical Garden. Columbia University Press, New York. 1977.

p.,

(24) Dalla Torre, C. G. de, and H. Harms.

Genera Siphonogamarum ad systema Englerianum conscripta. 921 p. G. Engelmann,
Lipsiae. 1900-07.

Standardizing range plant names for the Forest Service. Forest Worker 6(6): 13– 14. 1930.

(28) §Deam, Charles C.

Flora of Indiana. 1236 p., illus. Indiana Dep. Conserv., Div. For., Indianapolis. 1940. (Crataegus, 27 spp., by Ernest J. Palmer, p. 533–555, maps.) (29) §Dorn, Robert D.

Manual of the vascular plants of Wyoming. 1498 p., illus. (2 v.). Garland Publ., New York. 1977. (Crataegus, 4 spp., p. 1165–1166.)

(30) Eckenwalder, James E.

Re-evaluation of Cupressaceae and Taxodiaceae: a proposed merger. Madroño 23: 237-300. 1976.

(31) Fernald, Merritt Lyndon.

Gray's manual of botany: a handbook of the flowering plants and ferns of the central and northeastern United States and adjacent Canada. ed. 8, 1632 p., illus. American Book Co., New York. 1950. (Crataegus, 103 spp.—also 74 mostly local or hybrids-by E. J. Palmer, p. 767-801, illus.)

(32) Gilmour, J. S. L., F. R. Horne, E. L. Little Jr., F. Á. Stafleu, R. H. Richens, Ed. Comm.

International code of nomenclature of cultivated plants-1969. Formulated and adopted by the International Commission for the Nomenclature of Cultivated Plants of the I.U.B.S. Regnum Vegetabile 64, 32 p. Utrecht, Netherlands. 1969.

(33) Gleason, H. A.

The pronunciation of botanical names. Torreya 32: 53-58. 1932. (34) §Gleason, Henry A.

The new Britton and Brown illustrated flora of the northeastern United States and adjacent Canada. 3 v., illus. New York Botanical Garden. Hafner Press, New York. 1952. (Crataegus, 102 spp.-also 60 mostly local, hybrids, or forms-by Ernest J. Palmer, 2: 338-375, illus.)