This Atlas and Annotated List of the Vascular Plants of Arkansas is an attempt to update and improve our knowledge of the plants of the State, their distribution by county, and their chromosome number. It includes synonymy, common name, chromosome number. and voucher specimen citation. It is another step I believe toward the production (should adequate funding and time be found) of a Manual of the Vascular Plants of Arkansas.
The Atlas tells not only what we know of our wild plants, but indicates what we do not know; there are still many gaps in our knowledge of the Arkansas vascular plants. It also is useful as a predictor both of range and of chromosome number. For, example it is very likely that Asclepias tuberosa will be found in Newton County (known from all contiguous counties), but it appears unlikely that Asclepias syriaca would be found in Columbia or Union County. The chromosome number of Asclepias variegata is unknown but based on the 2n = 22 reported for other species of Asclepias it would very likely be 2n = 22 (or at least x = 11). Some species occur throughout the state or in two or more Natural Areas; others are limited to only one of the Natural Areas (these would be unexpected in counties of other Natural Areas).
Table 1 is a summary of the genera, species, subspecies, varieties, and total number of different taxa by family in the four major taxonomic groups of Arkansas vascular plants. The Dicots are, of course, the largest group and the Gymnosperms the smallest. The largest families are the Compositae, Gramineae, Cyperaceae, and Leguminosae. The total taxa for the state in this treatment is 2,469. This total does not include hybrids unless these are treated on par with normal species. This total represents a substantial increase (+131) over the total listed in the first edition of the Atlas, and reflects the renewed interest in the floristics of the state in the last decade. The total of 2,469 is considerably less then the 2,723 names listed by Demaree (1943), the difference being largely due to errors in Demaree's list as well as my synomymizing many varieties and not recognizing forms. An additional 137 names are listed in the POSSIBLE ADDITIONS list and 187 names appear in the ADDENDUM (some of these duplicate names in the POSSIBLE ADDITIONS or EXCLUDED NAMES list), for a total of about 324 potential additions to our flora. If all of these were, in fact, found in the State eventually (a very unlikely possibility), my total for the number of taxa in the state would be 2,793 (a number similar to Demaree's number). The EXCLUDED NAMES list contains a total of 375 taxa that have been reported for Arkansas, but which apparently do not actually occur in the state. Perhaps further research will show that a few of these do rarely occur in Arkansas.
The chromosome numbers of about 461 Arkansas taxa remain unknown. But this indicates that about 81% of the taxa in the state have had their chromosome number reported, an impressive proportion. It should be noted that most chromosome number reports are based on material collected outside of Arkansas, and that perhaps around 10% of the reports herein reported have been counted from Arkansas material. Since chromosome number sometimes differs in different parts of the range of a species, it is evident that much work remains to be done to check chromosome numbers in Arkansas representatives of the remaining 9O% (+ the 19% unknown group).
While many new state records (old species in new places) have been discovered in Arkansas in the last decade, it is noteworthy that new taxa (new to science) described in recent years in the state have largely been found in the Ouachita Mountains area. Since 1975, the following new taxa have been found in that area: Amorpha ouachitensis Wilbur, Hedyotis ouachitana E. B. Smith, Galium arkansanum Gray var. pubiflorum E. B. Smith, Cardamine angustata O. E. Schulz var. ouachitana E. B. Smith, Solidago ouachitensis C. & J. Taylor, and Carex ouachitana Kral, Manhart & Bryson. A total of six new taxa have been found during the same period in the reminder of the state: Carex bicknellii Britt. var. opaca F. J. Herm. and a new species in the Rosaceae (to be named soon) in the Grand Prairie area of the Mississippi River Aluvial Plain; Oenothera heterophylla Spach. subsp. orientalis Dietrich, Raven & Wagner, Fuirena bushii Kral, and Spiranthes ovalis Lindl. var. erostellata Catling in the West Gulf Coastal Plain; and Oenothera clelandii Dietrich, Raven & Wagner scattered in the state.
Table 2 is a list of the counties of Arkansas, in numerical order of total collections per county (dots and "R's") from the best- to- worst - collected county. (HTML version of this table provides access to county location maps and full checklists for each county) As a crude index, one could say that those counties in the first column (numbers 1-25) are well-collected, those in the second column (numbers 26-50) are medium-collected, and those in the third column (numbers 51-75) are poorly collected. However, it is clear that the state is rather poorly collected in general, and probably all those counties with less than about 600 collections should be considered poorly-collected. Many of these counties are in the southern and eastern sections of the State, in the West Gulf Coastal Plain and Mississippi River Alluvial Plain areas of Arkansas. Jefferson County, which is bisected by these two areas of the State, on the other hand, ranks 8th best collected county in the state - a tribute to Marie P. Locke's collecting efforts there. Some of the more difficult taxonomic groups (e.g. Carex) are poorly collected nearly throughout the State. Hydrophytes (Lemna, Potamogeton, etc.) are probably the worst-collected group in the State.
Table 3 is an alphabetical list of the counties of the State, showing the total collections per county. The grand total of this table (and Table 2) is 49,510 bits of distributional information. This is an increase of 8,568 bits of data from the 40,941 bits listed in the first edition of the Atlas. Such an increase in the last decade suggests the fluidity of floristic study and emphasizes the fact that floristic work for an area is never done (completed). In a sense, the Atlas provides 75 (the number of counties) X 2,469 (the number of taxa) - 185,175 bits of distributional information, because the absence of a particular taxon from a particular county is significant information, also. This presupposes that the flora of that county is well-known, which is not the case in the majority of our counties. Thus, the absence of a particular taxon in a particular county as shown in this Atlas is often due to our ignorance of whether or not the taxon occurs there, rather than to its actual absence.
In another and perhaps truer sense, this Atlas is my way of sharing my ignorance with you. Much work has been done on the flora of Arkansas, but much remains to be done. Some counties in the State are essentially "virgin territory", so little collecting has been done in them. I am hopeful that collectors in the State will find the Atlas helpful, and that it will stimulate them to help fill some of the large gaps in our knowledge about the presence and distribution of the vascular plants of Arkansas.