Ancient flowering plants: DNA sequences and angiosperm classification

Phylogenetic analyses of gene sequences provide a clear pattern of which extant flowering plant genera diversified earliest. Combined with complete genomic sequences, these data will vastly improve understanding of the genetic basis of plant diversity.     

A preliminary review of the modern classification systems of the flowering plants

The present paper is divided into three parts: 1. The first part is devoted to the review of the historical origin of the modern classification systems of the flowering plants. Early systems of classification since the Aristotelian time provided a basis for the modern schemes of classification. This paper has reviewed briefly the history of plant systematics, which is divided into three periods: the period of mechanical systems of classification, of natural systems of classification, and of phylogenetic systems of classification. The historical development of the plant systems and the basic idea for three periods is discussed respectively. This paper also considers that the studies of the modern classification system have been entering a new period which primarily aims at overall evolutionary respects. 2. Comparison of the modern classification systems of the flowering plants. Four main modern systems (i. e. A. Cronquist 1979, A. Takhtajan 1980, J. Hutchinson 1973 and A. Engler^,s system as revised by H. Melchior in Engler^,s Syllabus der Pflanzenfamilien 1964) which have greatly influenced the systemstics of plants are compared as to their systematical principles, basic concepts and systematic positions of higher taxa (orders and families) of the flowering plants. The paper is of the opinion that there is still much important work to be done in every field. 3. A review for the modern classification systems of the flowering plants. The paper reviews the modern classification of angiosperms from six aspects: a). The flowers plants are originated from a common ancestral stock; b). The flowers of angiosperms are homogeneous, stamen and carpel are phylletic sporangiophores, all flowers of angiosperms are comparable; c). Monocotyledons are originated from primitive dicotyledons, and represent phylogenetically monophyletic branch; d). The idea advocating the subdivision of Dicotyledoneae into Lignosae and Herbaceae should be rejected as pointed out by many authors; e). The systematical position of Hamamelidae is still a crucial subject for further research; f). The evolutional trends and evaluation of taxonomic characters must be considered in connection with the cor-relation to other characters in question.     

Numerical and comparative analyses of the modern systems of classification of the flowering plants

The modern classifications of Cronquist, Dahlgren, Takhtajan, and Thorne have been compared with one another and also with those published at the beginning of the 20th century, which comprise the ones by Bessey, Engler, Gobi, and Hallier. Mantel and consensus tests have been used to compare the different matrices taken from the above classifications. Results indicate that all four modern classifications do not differ from one another statistically. Ordinal delimitation has not changed significantly for a century at least: Orders of the modern classifications are similar to those of the past classifications. However, the topology or structure of Cronquist’s and Takhtajan’s classifications differs from that of Bessey’s. Also, Engler’s dicotyledon classification is statistically different from those of the modern systems. Among past classifications, that of Hallier resembles the modern ones most. The resemblance among the modern classifications and, in general, with the past ones can be explained by the similarity in taxonomic principles and in the practice used. Two other factors help in explaining similarities among classifications: cognitive constraint and historical inertia. For instance, the Linnean scheme—upon which all botanical classifications are based—imposes on the latter a structure which allows only with difficulty and approximation the representation of taxon evolution. Moreover, not only have modern authors mutually influenced one another (particularly Cronquist/Takhtajan, Dahlgren/Thorne), but also they have been influenced by past authors. Indeed, modern classifications are a reshuffling of past ones. Also, Engler’s influence is great, especially at the ordinal level. For changes and modifications to become effective in future classifications of flowering plants, one will have to minimize, if not avoid, the implicit influence of the modern systems as standard systems, and to count on, among others, molecular data in redefining taxonomic concepts founded on classical morphology, and consequently to remove the prudence that makes us look at classification as a useful convention for which one of the basic criteria remains the stability of taxa recognized long ago.     

Proteolytic enzymes from generative organs of flowering plants (Angiospermae)

Pollen proteases were discovered over 100 years ago, whereas the enzymes from female tissues have been used since the Roman era in simple biotechnological processes. In the last decade a great progress has been made in studies on plant proteases, including those from the generative organs. This paper reviews reports published in the last decade, concerning purification, properties and localization of proteases from generative parts of flowering plants against the background of the general proteolytic machinery of the plant. Special attention is paid to differences in protease structure and properties in comparison to other enzymes from the same catalytic classes. Participation of the proteases in all steps of pollen-pistil interaction as well as in pollen tube growth is discussed. Further intensive studies with use of native substrates are necessary to understand the role of proteases in pollination.     

Estimating attraction of Syrphidae (Diptera) to flowering plants with interception traps

Syrphidae with predaceous larvae are important predators of aphids and other insects and can be attracted and maintained in agricultural environments by the addition of flowering plants. Malaise interception traps baited with moveable flowering plants are a novel means of surveying for attractive species and can have the advantages of: (1) homogenising experimental site and plant quality, (2) portability, (3) continuous sampling, (4) capacity to simultaneously capture a broad range of insects (including pests) and (5) no requirement for additional sensory cues to be effective. Six of the 10 species of plants tested were relatively attractive (number of syrphids captured in flower-traps/numbers captured in no plant controls). While flower-traps captured more syrphid species than their associated controls, there were no differences between flower-traps and controls in the sizes (head height) or proboscis lengths of the flies collected. There were no significant relationships between relative attractiveness and flower width or depth or with plant height and floral area. Similarly, mean proboscis length of flies taken in flower-baited traps was not correlated with flower width or depth. The absence of the latter relationship may be due to the inability of an interception trap to distinguish between attraction and attraction-then-feeding.     

Self-incompatibility in flowering plants

Self-pollination in some groups of plants is prevented by a sophisticated biochemical signalling system. The molecule active in the female emerges as a highly charged glycoprotein, but the identity of the male determinant remains unknown. Studies of both the molecular biology and the physiology of the interaction suggest that the female polypeptide belongs to a family of glycoproteins which may play an additional, and more general, role in pollination. Pollen compatibility is controlled by one of two genetic systems and new information indicates a mechanism by which they may have arisen, together with the different stigma types with which they are correlated.     

How plants see themselves--self-incompatibility in flowering plants

Plants have been propagating themselves by cloning for millennia. It is, however, widely recognised that mixing genes with other individuals of the same species makes better evolutionary sense, as it provides the variation that is the raw material for natural selection. How, then, do some plants prevent self-fertilisation?     

Infraspecific categories in flowering plants

Infraspecific categories imply infraspecific classification, but there are few species whose internal diversity has been sufficiently studied to permit this in any detail. Important variation may be physiological, continuous and unassociated with convenient morphological markers. Conspicuous variation may be biologically trivial and the use of names for these variants gives a misleading view of the species-structure. If we are to classify we must know the relation between the internal and external characters. The suitability of a hierarchical system cannot be assumed. Informal classifications are likely to be of more use than those provided by the Code of Nomenclature. Nevertheless variation undesignated may easily become variation overlooked.     

Infraspecific categories in flowering plants

Infraspecific categories imply infraspecific classification, but there are few species whose internal diversity has been sufficiently studied to permit this in any detail. Important variation may be physiological, continuous and unassociated with convenient morphological markers. Conspicuous variation may be biologically trivial and the use of names for these variants gives a misleading view of the species-structure. If we are to classify we must know the relation between the internal and external characters. The suitability of a hierarchical system cannot be assumed. Informal classifications are likely to be of more use than those provided by the Code of Nomenclature. Nevertheless variation undesignated may easily become variation overlooked.