Warren H. Wagner

Polyploidy in Pteridophytes

Chromosome studies of pteridophytes had their major impetus in the work of Irene Manton (1) who was the first to show the far-reaching significance of Polyploidy in these plants. Her work was followed not only by numerous investigations by her own students at the University of Leeds but by researchers in many parts of the world, including especially India, Japan, New Zealand, Costa Rica, United States, Canada, Germany, Italy, and Hungary. Two major works have appeared in the past couple of years, namely the very thorough analysis of “Evolutionary Patterns and Processes in Ferns” by J.D. Lovis (2) and “A Cytotaxonomical Atlas of the Pteridophyta” by A Love, D. Love, and R.E.G. Pichi-Sermolli (3,4).

Cryptic Species, Species Delimitation, and Taxonomic Practice in the Homosporous Ferns

Biologists generally agree that species are to be delimited on the basis of genetic discontinuities. The two species concepts that depend on such discontinuities to delimit species are the biological and the evolutionary species concepts. A biological species is a group of interfertile populations that is reproductively isolated from other such groups and that occupies a specific niche in nature (following Mayr, 1982). An evolutionary species is a single lineage of ancestor-descendant populations that maintains its own identity from other such lineages, that fits into its own ecological niche, and that has a unique evolutionary history (Simpson, 1961; Grant, 1981; Wiley, 1981). It thus differs from the biological species concept in that it is equally applicable to both sexually and asexually reproducing organisms. Under both the biological and the evolutionary species concepts, genetic discontinuities between sister species are thought to arise stochastically following speciation. It is assumed that as time passes, the two diverge progressively in a suite of morphological, physiological, and ecological attributes. Although most botanists espouse an evolutionary species concept in their theoretical writings, in their classifications they often recognize only species that have distinctive structural characters by which the taxa can be identified. In so doing, they are employing the morphological species concept of their

Origin and Philosophy of the Groundplan-divergence Method of Cladistics

The Groundplan-divergence Method of constructing phylogenetic trees was created during the 1950s for illustrating systematic principles, but it was taken up widely by researchers carrying out monographic research. Based upon a study of certain Hawaiian ferns, the method attempts to deduce pathways of genetic change on the basis of phenetic evidence. It tries to estimate the amounts (grades), directions (clades), and sequences (steps) of phylogenetic divergence, using the con- cept of generalized or groundplan characteristics as the basis of judging primitive- ness. Groundplan-divergence analysis is concerned with pathways of actual biological changes rather than with their chronology (when the changes took place) or their geography (where they took place). Obvious parallelisms, reticulations, and co-ex- istences of ancestors and derivatives are accepted and embodied in the cladistics. The method involves the interplay of phenetic classification, the detection of taxa of hybrid origin, analysis of character trends, synthesis of generalized character states, estimation of divergence levels, grouping according to divergence formulas, and the connecting of lines with hybrid reticulations. The method is not able to overcome problems that are caused by such factors as major gaps in the phylogenetic record, important missing characters, excessive hybridization, and evolutionary pat- terns that involve massive randomness or overwhelming amounts of parallelism. Examples of various uses of this method are cited. In view of recent resurgence in cladistic theory and methodology, it seems appropriate to review the history and philosophy of the Ground- plan-divergence Method, one of the pioneering attempts to place the construction of phylogenetic trees on an objective basis. The method remains as useful today as it was when it was introduced over a quarter of a century ago for purposes of teaching principles of systematic botany. As will be seen, the approach is a conservative one, utilizing time-hon- ored ideas of phylogenetic induction and bringing them together in a particular way. The method is based upon traditional concepts of the relationships of classification to phylogeny. Although both are involved, it makes no claims for either perfect parsimony or complete compatibil- ity. It allows for a certain amount of parallelism as well as reticulation. The last, the origin of taxa by hybridization, has not previously been discussed in connection with Groundplan-divergence, nor for that matter has the entire method itself been reviewed in any detail, although various authors to be cited below have discussed various aspects of it. Until the 1950s, phylogenetic trees were based on subjective analysis and drawn without definite reference to evolutionary theories. There was no effort to quantify relationships and each author drew his tree intuitively. Little or no explanation went along with it. There was no 173

Generic Classification of Modern North American Lycopodiaceae

Generic classification of North American Lycopodiaceae is analyzed in terms of the general factors that govern the recognition of the rank of genus, the character states that determine affinities, the hypothetical common ancestral groundplan, a tree based on these data, and a translation of this information into a classification scheme. The genera segregated here are based primarily on numerous characters of anatomy, chromosomes, spores, and gametophytes. Those groups that are recognized as genera have many distinguishing features, strong gaps separating them from other groups, monophylesis, uniquely derived states, inability to hybridize, and a level of segregation consistent and comparable with generic division in other pteridophytes (...)

The Role and Taxonomic Treatment of Hybrids

plants upon which to base a discussion of the role and taxonomic treatment of hybrids. A number of questions are involved: What contribution do they make to the pattern of diversity of North American pteridophytes? How common are populations of natural hybrids in comparison to those of normal species? How likely are students and collectors to find and preserve them? To what extent are the geographical ranges of hybrids controlled by those of their parents? Finally, how should we designate them nomenclaturally in the Flora North America? As varieties of the parents? With formulas? Or with taxonomic binomials like

Systematic implications of the Psilotaceae

To assess the taxonomic relationships between the Psilotaceae and the Filicales ( = Polypodiales), certain factors including character divergence, gaps in the record, categorical consistency, conservatism of characters, and use of factual vs. hypothetical data have been given consideration. Although it has been proposed that the aerial shoots of Psilotaceae are homologous to fronds, and the appendages to pinnae, and that the Psilotaceae should be classified as Filicales,Psilotum andTmesipteris show a number of profound differences from Filicales. These involve the structure of the aerial organs, vascular patterns, fertile appendages, and sporangia. In view of the taxonomic criteria used, and the nature of the character differences, it is concluded that the Psilotaceae do not warrant inclusion in Filicales. InsteadPsilotum andTmesipteris constitute a separate line of evolution, and should be treated as a class, the Psilopsida, of Tracheophyta, equivalent to Equisetopsida, Lycopodiopsida, and Polypodiopsida.

Two Moonworts of the Rocky Mountains; Botrychium hesperium and a New Species Formerly Confused with It

The taxonomy of western North American botrychiums still needs much research. Interpretations of the past were based largely upon scanty and poorly prepared collections. For over 30 years only two B. matricariifolium-like moonworts have usually been accepted for this region-B. boreale subsp. obtusilobum (Rupr.) Clausen and B. matricariifolium subsp. hesperium Maxon and Clausen (Clausen, 1938). As to the former, we conclude that the western North American plant is not closely related to B. boreale, as will be discussed in a monograph of this genus currently in preparation. The correct name for taxon obtusilobum is B. pinnatum St. John (Fig. 1, a-g). Taxon hesperium also proves to be a distinct species, readily distinguished from B. matricariifolium A. Br. subsp. matricariifolium, which occurs in North America only east of the Great Plains (Fig. 2, h-n). With our recent opportunity to investigate large populations of these plants in the field in numerous localities, we are now confident of the distinctness of not only B. pinnatum and B. hesperium, but of a third element as well, which is described here for the first time. It is no surprise to discover a new species related to B. hesperium in western North America, where the rate of endemism among moonworts is the highest in the world. With some ten out of 14 of the described and undescribed species known only there, western North America is clearly the metropolis for this subgenus (Botrychium subg. Botrychium). Using primarily the sterile lamina as a basis, we

Complex Venation Patterns in the Leaves of Selaginella: Megaphyll-Like Leaves in Lycophytes

Venation patterns of the leaves of two lycophytes, Selagiella adunca and Selaginella schaffneri, do not fit the definition of microphylls as having a single, unbranched vein. Although S. adunca has a simple pattern, S. schaffneri has a complexity matching that of many megaphylls, with numerous branching veins. The veins of S. schaffneri undergo an average of 13 branchings (range, 8 to 21), and reticulation between veins is frequent. The discovery of this radical departure from the familiar microphylls of lycophytes indicates that complex venation patterns in leaves do not necessarily arise from fusion of whole branches. The microphyll may not be as structurally stable as formerly believed.

Dryopteris in the Huron mountain club area of Michigan

SummaryThe seven species of woodferns (Dryopteris) of the Huron Mountain Club area, a natural preserve in northern Michigan, are described briefly with respect to their habitats and chromosomes: (1) Shaded upland ravines (“D. dilatata,”D. intermedia, D. marginalis); (2) vertical rock cliffs (D. fragrans) ; (3) marsh and swamp (D. cristata, D. spinulosa, D. intermedia); and (4) rocky island habitat (D. filixmas, D. intermedia, andD. marginalis). Various sterile hybrids were found:D. cristata Xintermedia, D. cristata Xmarginalis, D. “dilatata” Xmarginalis, D. “dilatata” Xintermedia, D. intermedia Xmarginalis, andD. intermedia Xspinulosa. No new allopolyploid or apogamous hybrids were found. All of the crosses grow where the parents are close by, except thatD. cristata Xmarginalis occurs in marshes where the latter parent is absent. Chromosome studies yielded a number of new cytogeographical records, of which the following are of greatest interest:D. “dilatata” Xintermedia andD. “dilatata” Xmarginalis, both with ca. 82 unpaired chromosomes at meiosis;D. filixmas, with 82 pairs;D. filixmas Xmarginalis, 123 singles; andD. fragrans, 41 pairs. An attempt to identify the “Lake SuperiorDryopteris dilatata” gave negative results. It is not the same as “Western dilatata” nor is it conspecific with the easternD. campyloptera. It is now clear that two distinct taxa have been erroneously combined in the “Gray’s Manual Range.” Epidermal and indusial glands may be either present or absent in both of the eastern American taxa. Other observations on glands indicate that their presence does not necessarily mean that the plant is a hybrid withD. intermedia as one of the parents. Gland size and density vary considerably, and gland size is not necessarily correlated with sizes of other epidermal cells. As evidenced by the conditions in the Huron Mountain area we conclude that man-made disturbance is not a necessary condition for hybridization between species ofDryopteris. Crosses form naturally under the primitive conditions of forest and swamp.

A BIBLIOGRAPHY OF BOTANICAL CLADISTICS: I. 1981

A listing of papers and dissertations either using some type of cladistic analysis on a plant group or dealing with theoretical cladistics and written by a botanist. In addition, to facilitate studies in vicariance biogeography, this list includes the distribution of the taxa treated in the various papers.