Gymnosperm Phylogeny — A commentary on the views of S. V. Meyen

In his important contribution to the literature on gymnosperm phylogeny, “Basic Features of Gymnosperm Systematics and Phylogeny as Evidenced by the Fossil Record,” Meyen (1984) uses the classical comparative method of the morphologist and the “congregational” method, i.e., grouping by common characters, of the taxonomist. The latter may have led him to categorize some taxa on the basis of superficially similar, non-homologous characters because he used no apparently objective method to distinguish homoplasy. For this and other reasons, Meyen’s hypothesis of evolutionary relationship among gymnosperms cannot, at present, be accepted as any nearer the truth than several competing proposals. The major innovation of Meyen’s proposed phylogeny is the recognition of the clade, Ginkgoopsida, coordinate with Cycadopsida and Pinopsida. Ginkgoopsida encompasses Calamopityaceae, Callistophytales, Glossopteridales, Peltaspermales, Caytoniales, and Ginkgoales, among others. These taxa are considered to be related because, in Meyen’s view, they share the common character of primary platyspermy — i.e., the presumed platyspermic seed-type of the basal group, Calamopityaceae, is considered to have evolved directly from the pteridophytic condition of an ancestral form. This basis for Ginkgoopsida is weakened by the facts that no seeds have been discovered in organic connection with any calamopityacean and, except for the poorly-preserved seed-like structure,Spermolithus, all seeds that occur earlier in the geologic record than fossils of the Calamopityaceae are radiospermic. It is possible, therefore, that even if the platyspermic seed,Lyrasperma, found in association with the calamopityacean,Stenomyelon, were borne by that plant, it is secondarily platyspermic, having evolved from a radiospermic ancestor. The foundation upon which Ginkgoopsida was erected seems, therefore, to be rather tenuous. Other characters used by Meyen, both reproductive and vegetative are discussed. Some which he considers significant, are interpreted to be unimportant in denoting phylogeny, while others are interpreted to support alternative hypotheses. Meyen proposes that the Ginkgoopsida evolved from archaeopterid progymnosperms. This viewpoint seems to be based largely on his erroneous belief thatArchaeopteris was probably a seed plant that bore compound leaves. There is no definitive evidence that supports the view thatArchaeopteris bore seeds. On the other hand, there is strong evidence to support the contention thatArchaeopteris produced simple leaves (Carluccio et al., 1966; Beck, 1971), not compound leaves. Meyen’s phylogenetic proposal is based on data that can be and, in part, have been differently interpreted by others. Consequently, it deserves the careful and critical evaluation of all students of gymnosperm phylogeny.     

What shapes the range edge of a dominant African savanna tree,Colophospermum mopane? A demographic approach

Climate is widely assumed to be the primary process that limits the distribution ranges of plants. Yet, savannas have vegetation not at equilibrium with climate, instead its structure and function are shaped by interactions between fire, herbivory, climate, and vegetation. I use the rich literature of a dominant African savanna woody plant, Colophospermum mopane, to demonstrate that climate and disturbance interact with each demographic stage to shape this species range limits. This synthesis highlights that climate‐based predictions for the range of C. mopane inadequately represents the processes that shape its distribution. Instead, seed bank depletion and rainfall limitation create a demographic bottleneck at the early seedling stage. The legacy of top‐kill from disturbance changes tree stand architecture causing a critical limitation in seed supply. Exposure to top‐kill at all demographic stages causes a vigorous resprouting response and shifts tree architecture from that of 1–2 stemmed tall trees to that of a short multi‐stemmed shrub. The shorter, multi‐stemmed shrubs are below the height threshold (4 m) at which they can produce seeds, resulting in shrub‐dominated landscapes that are effectively sterile. This effect is likely most pronounced at the range edge where top‐kill‐inducing disturbances increase in frequency. The proposed mechanistic, demographic‐based understanding of C. mopane''s range limits highlights the complexity of processes that interact to shape its range edges. This insight serves as a conceptual model for understanding the determinants of range limits of other dominant woody savannas species living in disturbance limited ecosystems.     

Method of fixing the heterotic effect—implementation on plants (on the hundredth anniversary of the birth of V.A. Strunnikov)

The article is devoted to the 100th anniversary of the outstanding world-renown Russian scientist Vladimir Alexandrovich Strunnikov, Academician, Professor, Head of Group of Developmental Cytology and Sex Regulation at Koltzov Institute of Developmental Biology and Head of genetic studies on silkworms in a number of sericulture institutes in CIS. Laureate of the State Prize of the USSR (1981), Hero of Socialist Labor (1990), awarded the I.I. Mechnikov Gold Medal, Academy of Sciences of the USSR (1981), founder of the theory explaining the origin of heterosis. One of his most significant achievements is the “Methods of Fixing the Heterosis Effect,” which makes it possible to abandon the production of hybrid seed and increase the yield of many crops by 20–50%. Fixing the gene complexes that determine the heterosis effect will become the “springboard” that will allow obtaining even more productive heterotic hybrids on the basis of new-generation varieties. The efficiency of this method in plant objects at the organismal and molecular levels was shown in the All-Russia Research Institute of Rice. A modification of this method reducing its laboriousness and increasing its efficiency was developed.     

Heritability: What's the point? What is it not for? A human genetics perspective

Genetica - In this paper, we explain the concept of heritability and describe the different methods and the genotype–phenotype correspondences used to estimate heritability in the specific...     

Chemistry of the genus Sequoia—V. Cyclitols from the heartwood of Sequoia gigantea

The heartwood of giant redwood, Sequoia gigantea, has been shown to contain three cyclitols. The principal cyclitol was sequoyitol, followed by myo-inostiol and pinitol. The possible taxonomic relevance of cyclitol composition is discussed.     

Agronomic evaluation of prospective new crop species. V.Jarilla chocola—A proteinase source

Jarilla chocola (Caricaceae) was evaluated at two locations as a potential new crop. The fruits and tuberous roots of this dioecious, perennial plant contain proteinase. Results show limited potential because of intolerance to freezing, susceptibility to soil-borne pathogens, and only moderate fruit production. Partial shade and moist, well drained soils are required for adequate vegetative development. Seed require an after-ripening period for good germination. There were more male than female plants in small seedling populations, and these bloomed more profusely than female plants.     

Shallow lakes,the water framework directive and life. What should it all be about?

The European Water Framework Directive offers an unprecedented opportunity for improvement of ecological quality of both freshwater and marine systems. It has implications for every aspect of how catchments are used by human societies and could potentially mean a step change in how waters and catchments are managed. It must be implemented, however, by official bodies, which seem likely to apply ecologically outdated approaches, used in the past simply to manage water quality, to tackle the very different problem of improving ecological quality. Ecological quality can be characterised by parsimony of available nutrients, characteristic physical and biological structure, strong connectivity among systems and mechanisms of resilience to cope with normal, natural change. The implications of these are that high quality systems in a given location do not have unique lists of species and single formulae for how the biodiversity is constituted. They have considerable inherent variability whilst preserving their fundamental functional characteristics. This appears not to have been recognised by official bodies that seek simple taxonomic indices as measures of quality. To some extent this is a function of the way the Directive has been written, but a slavish adherence to this approach may undermine the spirit of the Directive and result in a failure to bring about the fundamental reform that is needed.