Venation


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venation

[ve′nā·shən]
(botany)
The system or pattern of veins in the tissues of a leaf.
(invertebrate zoology)
The arrangement of veins in an insect wing.

Venation

 

Leaves. Venation, or nervation, in leaves is the arrangement of veins in leaf blades. Four main types are distinguished. (1) One or more longitudinal veins do not branch and are not connected by crosspieces (in many conifers). (2) The branches of the veins are not connected by crosspieces and reach the leaf margins (in most ferns); venation is often bifurcated. (3) Veins proceed along the leaf almost in parallel (in many grasses with linear leaves), or they form arcs converging at the base and apex of the blade (in the lily of the valley) and connected by delicate transverse cross-pieces. Venation of this type (parallel-veined and arc-veined) is characteristic of most monocotyledons but is also present in some dicotyledons with linear leaves. (4) From one or more large first-order longitudinal veins, smaller second-order veins branch out that give rise to still smaller third-order branches, and so forth. The veins are connected by crosspieces in different directions. All the basilar tissue of the leaf is divided into portions surrounded by small veins. These portions are penetrated by very tiny branches of the conducting system that end blindly (pinnate or reticular-veined venation). This type of venation is characteristic of most dicotyledons but it is also found in some monocotyledons (in the canna, arum family, and so forth).

Venation is called palmate when several veins (the main one thicker than the others) separate at the base of the blade in radial fashion. The oldest and most primitive form of venation is dichotomic venation. Study and description of venation is very important in identifying both recent and fossil plants (in the form of impressions and so forth) from the leaves.

Insects. Venation in insects is the arrangement of veins in the wing. The number and arrangement of veins is an important taxonomic feature of orders, families, and other systematic categories of insects. Venation is particularly important in the classification of fossil forms.

L. V. KUDRIASHOV

References in periodicals archive ?
Trailing margin of forewings roundly convex, forewing venation with 2 branches of RP, ScP and RA fused, 6 branches of MP and 2 r-m crossveins.
Because odonate wing venation is complex and full of autopomorphies (Rehn, 2003), the set of wing characters of Erythemis provided a mostly unresolved tree (Fig.
on the basis of leaf architectural and venation features, as well as cuticular details.
The paper is organized as follows: a comparative analysis is carried out, aiming to develop wing venation topological homologies in selected species (and including data on intra-specific variability).
Based on RYDON (1971: 340), this genus does not include "Polygrapha" suprema, "P." tyrianthina and "P." xenocrates, since they have genitalia, alar venation and the sensorial patch of the different and non-congeneric palpi with cyanea.
Morphology and leaf venation of the leaf of Quiina acutangula.
Terminology and morphological characters of the adult, wing venation, and genitalia follow Sakai and Saigusa (1999), Kristensen (2003), Regier et al.
These include the narrowly ovate leaves 3-4 times as long as wide, with inconspicuous venation and margin subentire to finely serrulate, the glabrous peduncle 3.3-6 cm, 2-3 times longer than the leaves (Fig.
In February 2011, my colleagues Ruth Fischer, Andy Breeding, Eric Redman, and I formed Sustainable Collection Services (SCS) to pursue a venation on it his idea.
The genus was provisionally placed in Philopotamidae [17] based on similarities in forewing venation and additional species have been included [18].
Sarracenia flava , the yellow pitcher, has chartreuse flowers and pitchers, though often with marked venation and natural variation.
1.5 mm long, located on the rachis, between the proximal pairs to leaflets; rachis 35-125 mm long; interfoliolar segments 4-8 mm long; leaflets discolorous, 18-20 pairs, chartaceous, adaxial surface glabrous, abaxial surface pilose, 10-19.5 X 4-8 mm, oblong to obovate, apex obtuse to truncate, mucronate, base oblique, venation penninervous.