@article {20, title = {On the recent progress and present state of systematic botany}, journal = {Report of the forty-fourth meeting of the British Association for the Advancement of Science; held at Belfast in August 1874}, volume = {1874}, year = {1875}, pages = {27-54}, chapter = {27}, author = {Bentham, George} } @article {22, title = {Problem of the taxonomic category {\textquotedblleft}species{\textquotedblright} in cyanobacteria}, journal = {Algological Studies}, volume = {109}, year = {2003}, pages = {281-297}, chapter = {281}, abstract = {

Abstract: In Cyanobacteria (cyanophytes, cyanoprokaryotes) \“species\” has been traditionally defined on the basis of morphological characters (\“Geitlerian system\”) and these same criteria are still commonly used for identification of natural populations. Modern investigations, based on EM-methods and molecular sequencing have proven the differences between the genotypes which correspond more or less with the traditional phenotypic genera (revised after re-evaluation of morphologial characters). However, within genotypes enormous variability of natural morphotypes and ecotypes has been found and the same diversity has been confirmed in strains in cultures. Genotypically distinct species have not been confirmed, and the separation of them according to morphological criteria is problematic with respect to wide morphological variability. \– Because the purely traditional (morphological) concept of cyanobacterial species is frequently in disagreement with modern knowledge of cyanobacteria, the criteria for species delimitation should be changed. Taxonomic classification is always conventional; the definition of \“species\” in cyanobacteria is possible, if it will be based on rules developed in concordance with modern knowledge of morphology (phenotype variability and stability of different features), physiology, ecology and molecular bases of individual morpho- and ecotypes (e.g. morphospecies belonging to proved and distinct genotypes and characterised by ecological characterization).

}, keywords = {cyanobacteria, Cyanoprokaryotes, genus delimitation, nomenclature, species problem, taxonomy}, author = {Kom{\'a}rek, J.} } @article {12, title = {Species Delimitation: Inferring Gaps in Morphology across Geography}, journal = {Systematic Biology}, volume = {61}, year = {2012}, pages = {194}, chapter = {179}, abstract = {

Species are commonly delimited on the basis of gaps in patterns of morphological variation, but there seems to be little recent work on methods to objectively assess such gaps. Here, we introduce a statistical approach that uses measurements of continuous morphological characters and geographic variation in those characters to (i) measure the strength of the evidence for the existence of a gap in morphological variation between two hypothesized species and (ii) examine if a gap in morphological variation between two hypothesized species can be explained by an alternative hypothesis of geographic variation within a species. This approach is based on recent developments in analyses of multivariate normal mixtures, estimates of multivariate tolerance regions, and principal coordinates of neighboring matrices. We demonstrate the application of the approach by examining previously proposed hypotheses of species limits in the plant genus Escallonia. We discuss the main features of the method, including potential limitations, in relation to other approaches that use gaps in morphological variation as a criterion for species delimitation. The method we propose can help strengthen the link between the theory and practice of species delimitation by increasing the transparency and consistency of taxonomic decisions based on morphology, thus contributing to integrative approaches for species delimitation that consider morphological and geographic data on an equal footing with other kinds of information. [Geographic variation; morphological variation; normal mixture; operational criteria; species limits; tolerance limit.]

}, author = {Zapata, Felipe and Jim{\'e}nez, Iv{\'a}n} }