Vernon W. Proctor

HISTORICAL BIOGEOGRAPHY OF CHARA (CHAROPHYTA): AN APPRAISAL OF THE BRAUN-WOOD CLASSIFICATION PLUS A FALSIFIABLE ALTERNATIVE FOR FUTURE CONSIDERATION1

To that classification of the genus Chara, first advanced by Braun in 1847 with subsequent reiteration by the same author in 1867 and 1882 and by Wood in 1962 and 1965, an alternative is here proposed. Contended strengths of the present model include: i) a more accurate reflection of the phylogeny of the genus; ii) conformity with current distribution of dioecious taxa assumed consistently ancestral to their monoecious, morphological counterparts; iii) assumption of allopatric speciation primarily as a result of tectonic movement; and, iv) a foundation of underlying conjecture nearly all of which is potentially falsifiable in the Popperian sense as well as predictive with respect to a wide array of features. Deemphasized or rejected are previous assumptions that; i) stipulode, and to a lesser extent cortical, development reflect major evolutionary trends; ii) endemism is rare in the Charophyta; iii) dioecism and monoecism can be accommodated infraspecifically; iv) evolutionarily significant transitions between the preceding occur in both directions; v) hybridization contributed significantly to the phylogeny of the Charophyta; vi) section Grovesia is monophyletic in origin; and, vii) the Chara flora of Australasia arrived via India. The evidence upon which this classification rests is considered primarily with respect to the genus Chara, although the model appears equally applicable to the genus Nitella.

CHARA VULGARIS AND C. CONTRARIA : PATTERNS OF REPRODUCTIVE ISOLATION FOR TWO COSMOPOLITAN SPECIES COMPLEXES

Despite the voluminous literature devoted to delimitation of species (e.g. Mayr, 1957,1969; Hairston, 1958), a substantial divergence of opinion (or at least practice) continues to separate the relative position of many zoologists and vascular plant taxonomists from that of many cryptogamic botanists. Among the former, the biological species concept advocated by Dobzhansky (1941), Mayr (1963, 1969), Stebbins ( 1950) and others has gained wide acceptance while the morphological or typological species concept retains a dominant position among phycologists and bryologists. The biological species, genetically defined, is postulated to be an objective, natural, evolutionary unit deriving its identity primarily from the cohesive action of gene flow. However, this position has recently been challenged by Ehrlich and Raven ( 1969) who stress (1) the role of selection-vice gene flow-as the major cohesive force behind the phenetic uniformity of many large or disjunct populations, and (2) the importance of the local population as the primary unit of evolution. The typological species concept, on the other hand, is built around the notion that taxonomic relationships between organisms are essentially arbitrary and best determined by morphological approaches. We take the position that the identification of lines of reproductive incompatibility via experimental breeding techniques constitutes an effective, reproducible method of approaching the nature of species within the Charophyta. Using such techniques, we have attempted to (1) test the applicability of the Ehrlich-Raven position to

TAXONOMY OF CHARA BRAUNII: AN EXPERIMENTAL APPROACH1

Results from the present study suggest that Chara braunii encompasses a complex of geographical races or incipient species that although morphologically similar, are isolated to varying degrees ranging from partial interfertility to complete reproductive incompatibility. Most of the 6 clones studied were interfertile to the extent that fertilization was followed by the development of black oospores, but subsequent germination tests disclosed that many of these either failed to germinate or gave rise to offspring that were partially or completely sterile. No support was encountered for the suggestion that C. braunii is of recent development or that it has been distributed rapidly throughout the world.

CONSPECIFICITY OF SOME CHAROPHYTES(1).

Sweets Lake, British Columbia, is the type locality for plants originally described as Chara buckellii. Plants from this locality liave been crossed successfully to a second clone from Laguna La Drava, Argentina, the type locality for Nitellopsis bulbillifern. Plants from both clones were also crossed with others from Texas, New Mexico, and Wyoming that agree in most respects with. Robinsons original description of C. longifolia. On the basis of such crosses we suggest that all 3 taxa are biologically conspecific. There is no evidence, either from the field or experimental crosses, of gene flow between C. longifolia and C. hornemannii; the two should be considered separate species.

ELECTROPHORETIC ANALYSIS OF GENETIC VARIATION IN THE CHAROPHYTA. I. GENE DUPLICATION VIA POLYPLOIDY1

Electrophoretic analysis of 12 species of Chara indicates that functional gene duplication via polyploidy has commonly occurred in the genus. Duplication has been followed by differentiation of the loci encoding phosphoglucose isomerase (PGI). This has led directly to generation of substantial levels of genie variation both within and between taxa. A simple genetic model is proposed to account for the large array of PGI phenotypes encountered in natural populations. Constraints imposed by the reproductive biology of members of the genus, such as selfing, appear to have resulted in selective premiums on intrinsic mechanisms of generating genetic variation. Levels of variation in PGI were higher than would be predicted on the basis of charophyte reproductive characteristics; haploid loci segregate approximately two alleles within each species.