A key to families of Magnoliophyta will be published separately. Keys are included in each volume for all ranks below families if two or more taxa are treated. For dioecious species, keys are designed for use with either staminate or pistillate plants. Keys are also designed to facilitate identification of taxa that flower before leaves appear. More than one key may be given, and for some groups tabular comparisons may be presented in addition to keys.
Basionyms, with author and literature citation, are given for accepted names. Synonyms in common use are listed in alphabetical order, without literature citations. Common names in vernacular use are given in the appropriate language. In general, such names have not been created for use in the flora. Those preferred by governmental or conservation agencies are listed if known. The last names of authors of taxonomic names have been spelled out. The conventions of Authors of Plant Names (R. K. Brummitt and C. E. Powell 1992) have been used as a guide for including first initials to discriminate individuals who share surnames.
If only one infraspecific taxon within a species occurs in the flora area, nomenclatural information (literature citation, basionym with literature citation, relevant synonyms) is given for the species, as is information on the number of infraspecific taxa in the species and their distribution worldwide, if known. A description and detailed distributional information are given only for the infraspecific taxon.
Character states common to all taxa are treated in the description of the taxon at the next higher rank. For example, if corolla color is yellow for all species treated within a genus, that character state is given in the generic description. Characters used in keys are repeated in the descriptions. Characteristics are given as they occur in plants from the flora area. Notable characteristics that occur in plants from outside the flora area are given in square brackets or are included in a brief discussion at the end of the description. In families with one genus and one or more species, the family description is given as usual, the genus description is condensed, and the species description is as usual. In reading descriptions of vascular plants, the reader may assume, unless otherwise noted, that: the plant is green, photosynthetic, and reproductively mature; a woody plant is perennial; stems are erect; roots are fibrous; leaves are simple and petiolate. Because measurements and elevations are almost always approximate, modifiers such as "about," "circa," or "±" are usually omitted.
Arrangements of elements within descriptions of taxa are from base to apex, proximal to distal, abaxial to adaxial. General features such as growth form, persistence, habit, and nutrition are given first. For a particular structure or organ system, description of parts follows the order: presence, number, position/insertion, arrangement, orientation, connation, adnation, coherence, adherence. Features of a whole organ follow the order: color, odor, symmetry, architecture, shape, dimensions (length, width, thickness, mass), texture, base, margin, peripheral region or sides, central area, apex, surface, vestiture, internal parts, exudates. Unless otherwise noted, dimensions are length x width. If only one dimension is given, it is length or height. All measurements are given in metric units. Measurements usually are based on dried specimens but these should not differ significantly from the measurements actually found in fresh or living material.
Chromosome numbers generally are given only if published, documented counts are available from North American material or from an adjacent region. No new counts are published intentionally in the flora. Chromosome counts from nonsporophyte tissue have been converted to the 2n form. A literature reference for each reported chromosome number is available in the Flora of North America database (see below). The base number (x =) is given for each genus. This represents the lowest known haploid count for the genus unless evidence is available that the base number differs. Flowering time and often fruiting time are given by season, sometimes qualified by early, mid, or late or by months. Elevation generally is rounded to the nearest 100 m; elevations between 0 and 100 m are rounded to the nearest 10 m. Mean sea level is shown as 0 m, with the understanding that this is approximate. Elevation often is omitted from herbarium specimen labels, particularly for collections made where the topography is not remarkable, and therefore elevation is sometimes not known for a given taxon.
The term "introduced" is defined broadly to refer to plants that were released deliberately or accidentally into the flora and that now exist as wild plants in areas in which they were not recorded as native in the past. The distribution of nonnative plants is often poorly documented and may be ephemeral. The nature of introduced populations is discussed as far as understood.
If a taxon is globally rare or if its continued existence is threatened in some way, the words "of conservation concern" appear before the statements of elevation and geographic range, and a "C" is shown after the accepted name statement. Criteria for taxa of conservation concern are based on The Nature Conservancy¹s designations of global rank (G-rank), G1 and G2:
G1 Critically imperiled globally because of extreme rarity (5 or fewer occurrences or fewer than 1,000 individuals or acres) or because of some factor(s) making it especially vulnerable to extinction.
G2 Imperiled globally because of rarity (5-20 occurrences or fewer than 3,000 individuals or acres) or because of some factor(s) making it very vulnerable to extinction throughout its range.
Range maps are given for each species or infraspecific taxon. The maps are generalized and, in order to represent the probable range of a taxon, parts of states or provinces may be shaded even though documentation of occurrence there may be lacking. Occurrences in states or provinces listed in distribution statements are documented by specimens. We have assumed that details such as "northeastern Florida" are apparent on the map; consequently, directional qualifiers are not given in the list of territories, provinces, and states. Taxa that occur only in the flora area are indicated as endemic by an "E" after the accepted name statement. Authors are expected to have seen at least one specimen documenting each state record and have been urged to examine as many specimens as possible from throughout the range of each taxon. Additional information about distribution may be given in the discussion.
Distributions are stated in the following order: Greenland; St. Pierre and Miquelon; Canada (provinces and territories in alphabetic order); United States (states in alphabetic order); Mexico (11 northern states may be listed specifically, in alphabetic order); West Indies; Bermuda; Central America (Guatemala, Belize, Honduras, El Salvador, Nicaragua, Costa Rica, Panama); South America; Europe, or Eurasia; Asia (including Indonesia); Africa; Pacific Islands; Australia; Antarctica.
The discussion section includes information on taxonomic problems and interesting biological phenomena. Statements of economic uses supplied and documented by the author(s), Native American medicinal plants based on D. E. Moerman (1986), and weed status determined in consultation with weed specialist Robert H. Callihan are given in order to make this information more easily available to users of the Flora of North America North of Mexico. Weediness is indicated by codes W1 and W2 at the end of the accepted name statement. (The codes are references to publications that provide basic authority for the designation of weediness: D. T. Patterson et al. 1989 [W1] and R. H. Callihan et al. 1995 [W2]) Authors may provide additional discussions on the various aspects. Toxicity, if known, also is mentioned in the discussion, and pertinent literature is cited. (Please see Caution below.)
All genera, and approximately one out of three species, are illustrated. Illustrated taxa are marked with an "F" (for figure) following the accepted name statement. The illustrations may be of typical or of unusual species, or they may show diagnostic traits or complex structures. Most illustrations have been drawn from herbarium specimens selected by the authors. In some cases, living material or photographs have been used. Data on specimens that were used and parts that were illustrated have been recorded. This information, together with the archivally preserved original drawings, is deposited in the Missouri Botanical Garden Library and is available for scholarly study.
Major references used in preparation of a treatment or containing critical information about a taxon are cited after the discussion. These, and other works that are referred to briefly in the discussion or elsewhere, are included in the bibliography at the end of the volume and in the consolidated bibliography in the last volume of the flora.