21. Generic common names must not be misleading. Example: walnut refers to Juglans. Woods of other genera, which have different properties, should not be called kinds of walnut.

22. A few names widely used in several unrelated genera should be avoided altogether, to prevent confusion. Examples: ironwood, applied to Bumelia, Carpinus, Cliftonia, Cyrilla, Eugenia, Exothea, Krugiodendron, Ostrya, etc., and the hyphened names Catalina-ironwood, Lyonothamnus, and Arizona-ironwood, Olneya.

23. In the absence of a distinctive generic common name, the Latin generic name can be adopted as a common name. Examples: franklinia from Franklinia, magnolia from Magnolia, rhododendron from Rhododendron. (Sometimes scientific names have been derived from common names such as American Indian. Examples: Catalpa from catalpa; Olneya tesota from tesota.)

SPECIES

24. The English common name of a species generally should be two words (binomial). Example: white oak (Quercus alba). The second word (oak) is the name of the genus and corresponds to the Latin generic name (Quercus). The first word (white) designates the species or kind and corresponds to the Latin specific epithet (alba).

25. Some English common names are from other languages. Several are of American Indian origin. Examples: hickory, chinkapin, pawpaw, mesquite, saguaro. A few are from Spanish: madrone from madroño, pinyon from piñón. Lignumvitae is from Latin.

26. In the absence of a distinctive specific common name, a translation of the scientific name (specific epithet), usually descriptive, geographical, or personal, can be adopted as a common name. Examples: grand fir from Abies grandis, Sitka spruce from Picea sitchensis, Gambel oak from Quercus gambelii.

27. Indefinite terms of limited application should be avoided. Examples: the geographical terms "northern" and "southern." Others not appropriate in some parts of the range are "common" and "dwarf."

28. Sometimes the English common name consists of three words, generally not hyphened. Examples: Rocky Mountain maple, Acer glabrum; eastern white pine, Pinus strobus; California black oak, Quercus kelloggii.

29. A few tree species, especially in large genera, have wellestablished common names of one word, which omit the generic name. Four kinds are distinguished below.

A. Distinct species, usually of economic importance, long known by one word. Examples: peach, Prunus persica; avocado, Persea americana; pecan, Carya illinoensis; tamarack, Larix laricina.

B. The only species of a distinct (monotypic) genus. Examples: corkwood, Leitneria floridana; sourwood, Oxydendrum arboreum; desert-willow, Chilopsis linearis.

C. The only species native in the United States of a genus with foreign representatives. Example: tanoak, Lithocarpus densiflorus. American beech, Fagus grandifolia, may be designated simply as beech when the one native species is meant.

D. An important species in a small genus. Examples: Douglas-fir, Pseudotsuga menziesii (or also the genus Pseudotsuga); but bigcone Douglas-fir, Pseudotsuga macrocarpa.

30. The specific common name can be abbreviated to the one-word generic name in informal usage when the meaning is clear. Example: pine, for the only species of Pinus in a locality.

VARIETIES

31. The English common name of a tree species is applicable also to any included varieties.

32. English common names of botanical varieties (or subspecies) of trees are optional. Many minor botanical varieties need not be distinguished by separate English names. English common names of tree varieties generally are of three words, the first for the variety, the second for the species, and the third for the genus. Example: Delta post oak, Quercus stellata var. paludosa.

33. Typical varieties may not need separate English common names. The word "(typical)" can be added after the common name of the species to distinguish the typical variety from any other named varieties. In many species the typical variety is much more common than the other varieties and usually is meant when the two-word common name of the species is used. Example: slash pine, Pinus elliottii, has a named variety, South Florida slash pine, P. elliottii var. densa. The typical variety, P. elliottii var. elliottii, can be designated as slash pine (typical) or merely as slash pine, provided that the meaning is clear or is explained.

34. A distinct botanical variety may have an English common name of two words, if established in usage. Examples: cherrybark oak, Quercus falcata var. pagodifolia; Arizona pine, Pinus ponderosa var. arizonica; corkbark fir, Abies lasiocarpa var. arizonica.

HYBRIDS

35. Natural hybrids between tree species generally do not require special common names. Confusion is avoided by joining the common names of the parents with the word hybrid or cross, corresponding to a formula in scientific name. If needed, a distinctive common name corresponding to a binomial and a species may be given. Examples: longleafloblolly hybrid pine (from the formula Pinus palustris taeda); Sonderegger pine from the binomial for the same hybrid, Pinus ×sondereggeri). Artificial hybrids, which may differ with the same parent species, may be named as cultivated varieties (cultivars) under the Cultivated Code.

COMPOUNDING

36. Compounding affects the written form of common names but not pronunciation. The spoken language does not distinguish between two words, a hyphened word, and a solid word.

37. Compound words for tree names, formed from two or more words connected, are written either solid or hyphened. It is important that the words be united to convey a different meaning than that of separate words. Less important is whether the compound word is written solid or hyphened. Example: Douglas-fir ( or Douglasfir), but not Douglas fir (not a true fir).

38. Solid words are of three kinds:

A. Short words. Examples: tanoak, redcedar.

B. Words written as compound for many years. Gradually over a period of time the hyphen may be dropped. Examples: laurelcherry, honeylocust.

C. Words with a short, much used suffix referring to a tree or part. Familiar endings are bark, bean, berry, bush, leaf, nut, palm, plant, seed, thorn, tree, wood. (U.S. Government Printing Office, Style Manual, 1973, p. 277; 20.5.) Examples: corkbark, coralbean, serviceberry, butterbush, goldenleaf, bladdernut, royalpalm, velvetseed, buckthorn, coffeetree, cottonwood. However, some long words are hyphened for clarity. Examples: fishpoison-tree, firecracker-plant.

39. Hyphened words are of three kinds:

A. Words, mostly long, where the hyphen helps in reading and pronouncing, by indicating syllables or silent vowels. Examples: incensecedar, white-cedar, saw-palmetto, button-mangrove, jungle-plum, yellow-poplar, cypress-pine, desert-willow.

B. Words formed from a proper name. (U.S. Government Printing Office, Style Manual, 1973, p. 277; 20.2, 20.5.) Examples: Douglas-fir, California-laurel.

C. Words derived from three or more words. Examples: myrtle-ofthe-river, seven-year-apple.

40. Compounding serves to separate trees of unrelated genera that have been known by the same common name. Examples: cypress, Cupressus, and baldcypress, Taxodium; mangrove (red mangrove), Rhizophora, black-mangrove, Avicennia, white-mangrove, Laguncularia, and button-mangrove, Conocarpus.

SPELLING

41. Nouns, being shorter, are preferred to adjectives in English specific names. Examples: narrowleaf cottonwood (not narrow-leaved), Populus angustifolia; New Mexico locust (not New Mexican), Robinia neomexicana.

42. Personal names are shortened by omission of possessive ending ('s). Examples: Engelmann spruce (not Engelmann's), Picea engelmannii; Nuttall oak (not Nuttall's), Quercus nuttallii. Where there may be confusion between the names of a person and of an idea or thing, the personal name is capitalized and written in possessive form without the apostrophe. Example: Browns hickory, Carya brownii.

CAPITALIZATION

43. English common names of trees preferably are written with only proper names capitalized. However, all words may be capitalized, if desired, to designate approved common names clearly equivalent to scientific names and to avoid ambiguity.

REFERENCES

44. The 12 reference titles are designated here by number (27, 32, 52, 55, 85, 92, 115, 121, 122, 123 125, 126) and are listed under References, p. 25.

APPENDIX 7

BOTANICAL INDEX OF PLANT FAMILIES AND GENERA This index shows the botanical classification and relationships of the genera of native and naturalized trees of continental United States in plant families and supplements the alphabetical order of the main list. The classification used here and in the 1953 checklist is the standard conservative one by Dalla Torre and Harms (24), in which both families and genera of seed plants are numbered. It has been widely adopted by large herbaria in filing specimens and by the International Code of Botanical Nomenclature in listing conserved and rejected generic names. Also, following the Englerian system, it is the best known, most detailed, and most convenient. Obviously, a list in a straight line does not show detailed relationships, which are branching and treelike, perhaps sometimes uniting like a network.

First, the Alphabetical List of Plant Families cites Dalla Torre and Harms family numbers. Second, the Botanical Index, like a table of contents, contains the plant families and genera in natural arrangement by number, with Checklist page numbers of genera added.

ALPHABETICAL LIST OF PLANT FAMILIES

The native and naturalized trees of continental United States are classified under 76 plant families, listed below alphabetically. Of these, 73 are native and 3 (designated by small capitals) are naturalized and without native species. With very few exceptions, family names end in -aceae.

BOTANICAL INDEX

The 76 plant families and 244 genera of native and naturalized trees of continental United States are arranged numerically by the Dalla Torre and Harms numbers at left, checklist page numbers of genera at right. The naturalized groups (designated by small capitals) without native species total 3 families and 24 genera.

Names of larger groups of seed plants (spermatophytes) in which the families are placed, are inserted as center heads. The 3 subfamilies of the large legume family, Leguminosae, are noted. English common names for both families and genera and widely used synonyms of scientific names are listed. Following each family name is the number of genera with native trees (indicated by the abbreviation g.) and in parentheses the number of genera with naturalized trees, if any; then follows the total number of native species with the number of naturalized species in parentheses. Example: 21. Palmae, palm family, 8 g. (1 g.), 11 (1).

Dalla Torre and Harms numbers here are incomplete and not consecutive because many families and genera of seed plants of the world are not represented. Several names accepted at a later date are indicated by a letter inserted after the number.

The Botanical Index can be used to find where a genus is classified and also the names of related genera. Abies, or fir, will serve as an example. As listed on page 33, the family is Pinaceae. In the Alphabetical List of Plant Families above, Pinaceae is family number 6. Then, in the Botanical Index below, family 6, Pinaceae, with English common name pine family contains, including Abies, 6 genera listed by number according to relationships. Added for ready reference are English common names and page numbers.

Another use of the Botanical Index is to list the genera of native and naturalized trees belonging to each plant family. For example, to obtain names of the tree genera in the family Leguminosae, first, find the family number, 128, in the Alphabetical List. Then under family 128 in the Botanical Index are 19 native and 2 naturalized genera, grouped according to their relationships.