R. James Hickey

Habitat, evolution, and speciation in Isoetes

Species of Isoetes are notorious for the difficulties they present in identification. These difficulties are attributable to a series of habitat adaptations that have resulted in morphological simplicity, homoplasy, and reticulate evolution. Internal air chambers in the leaves of all taxa indicate that primitive Isoetes was aquatic. During the breakup of Gondwana, ancestors of modern taxa appear to have passed through a terrestrialization phase, which was accompanied by development of several morphological novelties and reductions including the evolution of sclerotic phyllopodia. This adaptation appears to have evolved after separation of the Indian subcontinent (...)

The Species Concept in Pteridophyta with Special Reference to Isoetes

The definition, description, and identification of Isoetes species has always been difficult. This is primarily the result of an overall morphological simplicity and extreme phenotypic plasticity that combine to reduce the number of stable and therefore diagnostic characters. Such aspects of the biology of Isoetes have, historically, resulted in rather diverse specific treatments and circumscriptions. Recent studies in the genus have tended to emphasize previously overlooked characters and to apply both modern experimental techniques and the principles of population genetics in order to resolve many of these inconsistencies. Investigations utilizing cytological data, germination and hybridization studies, and protein electrophoresis have shown that over the range of a species its boundaries vary due to clinal variation, non-patterned geographical variation, interspecific hybridization, and the production of fertile allopolyploids. Such approaches have greatly increased our understanding of the dynamics of this genus. At the outset, it should be stated that it is not the objective of this paper to discuss the theoretical implications, or the limitations and benefits of the various species concepts that are currently in existence. Such discussions are numerous and can be found throughout the pages of many of the major systematic journals such as Systematic Botany, Systematic Zoology and Biology and Philosophy. Rather, this paper is designed to illustrate both the current and the historical application of the various species concepts in pteridophytes with particular reference to Isoetes. It is hoped that the reader will come away with an appreciation of the progressive nature involved in the elucidation of species and for the (practical) necessity of applying multiple species concepts during any given systematic inquiry (see also Zander, 1985). To illustrate such processes the following examples will be presented: the I. storkii aggregate of Costa Rica; the I. melanopoda complex of the southeastern United States; and the Isoetes species of northeastern North America. As a prelude to these examples, a brief review of the species concept and a discussion of the role of herbarium material will be presented. Species concepts.-For the purposes of this paper, the species concepts of consequence are: the typological species concept (TSC), the morphological species concept (MSC) and the biological species concept (BSC). The TSC is associated with all poorly known groups. Typically it is associated with rare or at least rarely collected species and is almost always employed when only a single collection is known for the species; i.e., simply, the species is circumscribed upon the only materials available-the type. The MSC, the traditional concept of

The Early Evolutionary and Morphological Diversity of Isoetes, with Descriptions of Two New Neotropical Species

Two new Isoetes from South America are described and contrasted with morpholog- ically similar and sympatric species. The first of these species, I. baculata, represents a relictual morphotype within the Isoetaceae as indicated by the presence of completely laminate leaves. The other species, I. eshbaughii, is unique in forming desiccation resistant foliar gemmae which are completely enclosed by sclerified scales. Analyses on the distribution of alate leaves and scales, as well as peripheral fibrous bundles and sporangial pigmentation, show that there are nested sets of species within the Isoetaceae which represent major phylogenetic lineages. The pattern of character nesting suggests an historical transition from a primitively aquatic habit to a seasonally amphibious one, with subsequent parallel reversions back to aquatic zones. These habitat changes have resulted in convergent morphologies which are in large part responsible for the previous confusion re- garding the evolution of the genus and the dependence on megaspore morphology as the sole basis of infrageneric classification. A major advantage of the proposed phylogeny is that the de- marcation of major lineages now allows for the establishment of functional ingroups and outgroups, and thus provides a frame of reference from which additional phylogenetic hypotheses can be formulated. The Isoetaceae are a small, cosmopolitan family of aquatic, heterosporous pteridophytes which are related to the extant Selaginellaceae and Lycopodiaceae. The family is monotypic and comprises some 150 species (Tryon and Tryon 1982) which are classified primarily on the basis of megaspore surface morphology (Pfeiffer 1922; Fuchs-Eckert 1982). The classifi- cation of such a large number of species on the basis of variation in a single character is intu- itively suspect and several taxonomic studies indicate that this suspicion is warranted (Du- thie 1929; Williams 1943). Before the establish- ment of an infrageneric classification system

A Re-evaluation of Isoetes savatieri Franchet in Argentina and Chile

Abstract Isoetes savatieri has traditionally been interpreted as being a uniform aquatic ranging from the southernmost regions of South America to the central Andes of Chile and Argentina. An examination of herbarium material supports the recognition of two taxa, a southern I. savatieri and a more northern I. chubutiana, from central Chile and Argentina. The latter taxon is hexaploid and described here as a new species. The morphology of these species suggest that they are sister species resulting from divergence following a polyploidy event. These species, and several other species pairs, provide the best and, to date, only examples of allopatric divergence in polyploid Isoetes.

Chromosome numbers of neotropical Isoëtes

Chromosome counts have been made for a number of Isoetes found in eastern North America, Europe, and India. Typically the haploid complement of n= 11, or a multiple thereof, has been reported (Love et al., 1977; Kott & Britton, 1980). Polyploid series range from 2n = 22 to 2n = 110. The aneuploid I. durieui is notable in having the lowest chromosome number in the genus, with 2n = 20. Several taxa from India, including I. coromandelina Linn. f., I. panchananii Pant & Srivastava, I. indica L. Rao, and I. pantii Goswami & Arya, are reported to possess one or two supernumerary chromosomes (Goswami, 1975; Pant & Srivastava, 1965). Only Stylites gemmifera Rauh [= Isoites andicola (Amstutz) L. D. Gomez] shows a strong deviation from the presumed base number of x= 11. According to Rauh and Falk (1959), the diploid number for this species is ca. 58. Mexico, Central America, the Antilles, and tropical South America, with over fifty taxa, are exceptionally rich in Isoites. In addition, the morphological diversity in these taxa is perhaps greater than in any other part of the world. Among the neotropical species, only the count for I. andicola has been reported (Rauh & Falk, 1959). As part of an overall systematic revision of the Neotropical Isoetes, the chromosome numbers of several species were studied and are reported here. Some of these counts have been previously mentioned in Tryon & Tryon (1982), at which time I ascribed a count of 2n=44 in I. ticlioinsis H. P. Fuchs nom. nud. to I. lechleri Mett.

Systematics of the Northern Andean Isoëtes karstenii Complex

Abstract The Isoëtes karstenii complex includes those species characterized by laevigate megaspores, acute to free ala apices, a highly reduced labium, and distributions in the high altitude páramos of Venezuela, Colombia, and Ecuador. These species have been variously treated in the literature. Many early authors placed all Andean laevigate-spored specimens in Isoëtes lechleri, a central Andean species, while one later author recognized up to eight northern Andean species distinct from I. lechleri. This research represents a revisionary study to determine the number and identity of the taxa in this complex. Multivariate and descriptive analyses of morphological data and chromosome counts were performed. Five species are recognized including the previously described I. karstenii and I. palmeri. One variety is transferred from I. lechleri to I. karstenii (I. karstenii var. anomala). Three of the recognized species are newly described: I. fuliginosa, I. hemivelata and I. precocia. Chromosome counts revealed that I. karstenii and I. precocia are diploids (2n = 22) and that I. palmeri is tetraploid (2n = 44). Estimates of chromosome number based on spore size for I. fuliginosa and I. hemivelata indicate that they are polyploid (2n ≥ 44).

Levels and Patterns of Genetic Variation in Isoetes karstenii with Observations on I palmeri

Genetic variation was surveyed in eleven populations from throughout the range of the diploid Isoetes karstenii, as well as in two populations of a closely related tetraploid, I. pal- meri, using allozyme electrophoresis. Genetic variation was high in I. karstenii and appears to be highly structured, as evidenced by analyses of F-statistics and genetic vs. geographic distance. No fixed unique alleles were found that could distinguish between I. karstenii and I. palmeri, although one allele was observed that was unique to I. palmeri. These analyses confirm earlier observations suggesting low levels of interpopulational gene flow and have implications for sampling strategies. Isoetes karstenii A. Braun was first described based on a collection from the high-altitude paramos of Merida, Venezuela (Braun, 1862). Since that time it has variously been accepted or synonymized by subsequent researchers, yet no detailed discussions of its variation or distribution have been published. As part of continuing research aimed at characterizing the neotropical species of Isoetes, we performed a survey of genetic variation in I. karstenii from throughout its range, as well as in a pair of populations from a single locality of a related species, I palmeri H.P. Fuchs, using allozyme electrophoresis. A taxonomic revision of the species complex to which these taxa belong is cur- rently in preparation (Small and Hickey, in prep.).

The Genus Ernodea (Rubiaceae) in the Caribbean Basin. II. Morphological Analyses and Systematics

The genus Ernodea, consisting of erect or prostrate shrubs, has been thought to consist of nine species, most of which are endemic to the Bahamian Archipelago. The classification of the genus is difficult because the original species descriptions are incomplete and include characters of great plasticity. Addition- ally, reproductive and genetic studies failed to provide evidence to support recognition of distinct species. We measured 30 floral and vegetative characters from samples representing all taxa and distributed across the entire range of the genus to delimit relationships at the specific level and to delineate morphological gaps within the genus. Phenetic analyses involving Principal Component Analysis and Canonical Discriminant Analysis provided consistent separation of two main clusters; each cluster separated into two subclusters. Vegetative characters provided better discrimination than floral characters. In contrast to the current literature, this study recognizes four morphological species: E. cokeri, E. littoralis, E. taylori and E. millspaughii. The morphological and ecological diversity of Ernodea in these islands suggest that there has been rapid divergence associated with adaptive radiation. A key to the species with descriptions and nomenclature is provided.

Analysis of morphological and anatomical characteristics of isoetes using Isoetes tennesseensis

The three known populations ofIsoetes tennesseensis were examined to document and analyze their morphological and anatomical characters. Characters examined included velum coverage, lacunae, leaf form and size, sporangial wall cells, and ligule and labium morphology. Three types of morphological patterns were found: stable, variable, and dimorphic. The discovery of dimorphism between mega- and microsporophylls for velum coverage, velum length, sporangium size, and ligule shape is of particular interest. This study presents a model for future work designed to complement current species descriptions and it establishes a baseline for morphological comparisons with otherIsoetes.

The Lycopodium obscurum Complex in North America

assumes a fastigiate growth habit, thus mimicking L. dendroideum, for which it is most commonly mistaken. It is this mimicry, coupled with the occasional intergradation between L. obscurum var. obscurum and L. obscurum var. isophyllum, that is largely responsible for the belief that there is complete intergradation between L. obscurum and L. dendroideum. The general morphology and growth habit of all three taxa are so similar that in the individual descriptions mention will be made only of those characters where significant differences have been noted. All of the taxa dealt with in this paper share the following characteristics: Subterranean rhizome clothed with sparse, broad and rounded, scale-like leaves; rhizome anisodichotomously branched with 1 upright leafy aerial shoot and 1 usually weak secondary rhizome produced each year; aerial shoots 8.0-19.0 (mean 12.5) cm from soil level to the base of the strobili, with 3 or 4 lateral branch systems along the aerial axis, each system dichotomously branched 3 or 4 times to produce 8-16 lateral branchlets. Growth of the entire aerial shoot system is also similar in the three taxa. It continues for 4-5 years, and microphyll constrictions are present throughout the aerial portions. Dichotomous branching in the lateral branch systems is concentrated in the second growth season, with occasional dichotomies formed during the third growth season as well. Leaves of the lateral branchlets are normally 6-ranked and in two pseudowhorls of three leaves apiece, producing a phyllotactic fraction of 2/6. All leaves are strongly decurrent. Strobili, produced in the (sec