Leaf Venation Patterns Research Articles

Leaf Vascular Pattern Formation.

The pattern and ontogeny of leaf venation appear to guide or limit many aspects of leaf cell differentiation and function. Photosynthetic, supportive, stomatal, and other specialized cell types differentiate in positions showing a spatial relationship to the vascular system. These spatial relationships are of obvious importance to leaf function, which relies on venation for the servicing of cells engaged in photosynthesis, gas exchange, and other leaf processes. Although the need for coordinated organization of cell types around the vascular system is clear, the means by which this is achieved during development is not well understood. In the few systems in which it has been possible to follow the ontogeny of the venation along with the differentiation and function of surrounding cell types (e.g., in C4 grasses), observations suggest that the developing vascular system may have a role in providing positional landmarks that guide the differentiation of other cell types. Another possible explanation is that an underlying pattern guides the differentiation of both venation and surrounding cells. Whether the process of vascularization creates or reveals a pattern, studies to date are largely descriptive, and little is understood of the underlying mechanisms. These mechanisms must be highly regulated, as evidenced by the successful use of species-specific leaf vascular pattern as a taxonomic characteristic (e.g., Klucking, 1992) and by the predictable effect of certain mutations. In this review, we summarize the vascular patterns and their ontogenies in dicots and monocots, referring extensively but not exclusively to Arabidopsis and maize as examples. We also discuss a variety of models that seek to explain vascular pattern formation, and we provide a summary of molecular and genetic investigations of the process.

Hydrodynamic Modelling Study of Angiosperm Leaf Venation Types

AbstractThe morphology of leaf venation has been studied repeatedly and various systems have been proposed for the classification of the observed leaf venation patterns. Almost nothing is known, however, about the functional properties of the various venation types. Using a computer modelling approach we analysed the water transport properties of typical craspedodromous and brochidodromous venation patterns. The water transport through the leaf and the veins was modelled as a fluid flow through a porous medium and the mathematical model was solved with the Finite Element Method. The simulations illustrate that the leaf margin represents a critical region in terms of water supply. The results provide a plausible functional explanation for three well known phenomena: 1) the correlation between craspedodromous venation and the formation of leaf teeth; 2) the fact that craspedodromous venation is more common in temperate than in tropical regions and 3) the fact that xeromorphic leaves tend to have more closed venation.

The systematic value of leaf venation patterns of Viola species in Korea

The systematic value of leaf venation patterns of Viola species in Korea

Pectinal veins: a new concept in terminology for the description of dicotyledonous leaf venation patterns

Mid-Cretaceous dicotyledonous leaves frequently exhibit continuous variation in venation patterns. This poses considerable problems when concise description and taxonomic partitioning of leaf material is attempted. Often it is extremely difficult to differentiate consistently between pinnate and palmate organization. A new terminology is proposed that dispenses with the need to differentiate between pinnate and palmate organization or between primary and secondary vein orders which commonly intergrade. Emphasis is placed upon the pattern of vein courses and branching hierarchy which provides unambiguous reference points for architectural descriptions and analyses.

A morphological and embryological study of Callicoma serratifolia Andr. (Cunoniaceae).

The morphological and anatomical features of Callicoma serratifolia populations on the New England Tablelands reveal the existence of two distinct groups, here designated A and B. Major morphological differences between these groups include leaf margin serration, distribution of hairs on stems and branches, possession of one trichome type in group A in contrast to two types found in group B, overall leaf size and venation patterns. At the anatomical level the differences are in vessel dimensions and the number of bars on perforation plates. Features common to both groups include bisexual, pentamerous and apetalous flowers, tetrasporangiate versatile anthers with a glandular tapetum, simultaneous cytokinesis in pollen mother cells and colporate pollen which is released at the 2-celled stage. The ovules are anatropous, bitegmic and crassinucellate with a polygonum type of embryo sac development. The endosperm is of the nuclear type. Both integuments contribute to the formation of the seed coat. The embryo is straight. While in its vegetative anatomy C. serratifolia resembles members of the families Eucryphiaceae, Saxifragaceae and Escalloniaceae, embryologically it closely resembles Baueraceae and less closely the subfamily Hydrangeoideae of the Saxifragaceae.

Leaf Anatomy and Venation Patterns of the Styracaceae

Leaf Anatomy and Venation Patterns of the Styracaceae

Studies on the leaf anatomy of Euphorbia: III. The node

Anatomical studies of representatives of 11 groups of species of the genus Euphorbia, erected on the basis of leaf venation patterns, reveal the occurrence of 3 main types of nodal organization, viz. unilacunar 1-trace, bilacunar 2-trace and trilacunar 3-trace (in the majority of the species). In some instances, a deceptive multi-stranded condition is visualized if cleared leaves alone are studied. Euphorbia polygonifolia and E. peplis leaves have a variable vascular supply in the same plant, consisting of 2 or 3 strands in the former and 2 or 4 strands in the latter. No correlation was found between the type of node and either the habit and habitat of the plant or the leaf shape and size.

Studies on the leaf anatomy of Euphorbia: II. Venation patterns*

Leaf venation patterns of 150 species of Euphorbia are presented and their value as a diagnostic feature in the genus assessed. Based on the gross venation patterns, the species have been grouped into uni-, bi-, tri-veined and special categories. The majority of the species studied belonged to the tri-veined category, in which ornamentation of the veins and the course of traces in the lamina proved useful additional characters. Features such as the size of the areoles, the number of vein endings, and their further ramifications and composition in each areole varied in the same leaf or in different leaves of a given species. Furthermore, no direct correlation could be established between the areole size and the numbers of vein endings and tips per areole. Forty species possess a parenchymatous vein sheath. Globular chloroplasts showed up conspicuously in the sheath cells of a few species. Dilated tracheidal elements, localized on the venules or at the tips of vein endings, are characteristic of the xerophytic species. In some instances, correlation was apparent between plants grouped according to their venation patterns and their habit.

Reply to Criticism of Hypothesis of Leaf Venation and Angiosperm Origins

Alvin and Chaloner's criticism of my ideas about leaf venation patterns seems to be based chiefly on the distribution of vein junction types to the exclusion of associated vein island types. It is necessary to emphasize, therefore, that the glossopterid syndrome includes characters belonging to both of these categories. From the phylogenetic standpoint the important correlations are those between the complete syndrome and the major taxa: Angiospermae, Glossopteridae, Pteridospermae, Cycadales, Bennettitales and Caytoniales. Parts of the syndrome are lacking from all of these groups except the first two. What the critics do show is that similarities in the venation systems extend beyond that of open dichotomy—the Ginkgo and Circaeaster stage—as far as the Gangamopteris stage. We can agree to parallel evolution in these groups up to the Gangamopteris stage. Confining the discussion, for the moment, to leaf characters, there are some other features to be taken into account. The examples cited for the Pteridosperms, cycads and Bennettitales are all of leaflets of compound pinnate leaves, whereas the comparison was made between simple leaves in the Glossopteridae and Angiospermae. Compound pinnate leaves occur frequently in only about 20 per cent of angiosperm families and in many of these there is internal evidence of a derivation from simple leaves. One exception, the Quiinaceae, has already been commented on. The only other major exception is the Leguminosae in which the evidence is consistent with the persistence of compound leaves since the glossopterid phase of evolution.

Parallel Evolution in Leaf Venation: an Alternative View of Angiosperm Origins

MELVILLE1 advanced the hypothesis that leaf venation patterns of flowering plants provide a body of evidence-suggesting the origin of angiosperms from the Permian Glossopteris and its allies, which flourished on the old continent of Gondwanaland. He shows that Glossopteris-like venation patterns are encountered in several living angiosperms, and emphasizes that most significant examples are found in regions which once constituted the Gondwanaland continent. His argument hinges on the extent to which these venation patterns can be said to resemble closely Glossopteris rather than other gymnosperm leaf types. This proposition can seriously be called in question.

Leaf Venation Patterns and the Origin of the Angiosperms

Evolution of the angiosperm leaf is traced through venation patterns by comparing those of living plants from the countries which formed Gondwanaland with the fossil record.

The juvenile leaves ofBolbitis

The morphology of the juvenile leaves of three species ofBolbitis is described, and the progression of the leaf form and venation pattern from the cotyledonary leaf to the adult condition is traced. The leaf lamina becomes bipinnate, from the obcuneate simple condition, in the successive juvenile leaves and then reverts to the simply pinnate adult form. In addition to glandular hairs of the type found on the adult leaves, the juvenile leaves bear long acicular hairs. The possible significance of these peculiarities in phyletic studies is discussed.