Phyllotaxy


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Related to Phyllotaxy: alternate phyllotaxy

phyllotaxy

[¦fil·ə¦tak·sē]
(botany)
The arrangement of leaves on a stem.

Phyllotaxy

 

the arrangement of leaves on the stem, reflecting the symmetrical structure of a shoot. Leaf arrangement, which depends primarily on where the leaf primordia arise on the stem apex, is usually an element in the taxonomy of plants. There are three principal types of phyllotaxy: alternate, if one leaf occurs at each node of the stem (oak, birch, grasses, the Umbelliferae); opposite, if two leaves appear at a node on opposite sides (maple, lilac, the Labiatae); and whorled (verticillate), if more than two leaves appear (oleander, water thyme, water milfoil).

The common feature of all three types of leaf arrangement is equal angular distance between the leaves that are at the same node or on successive nodes of a spiral, which is called the basic genetic spiral. Opposite and whorled leaf arrangement is characterized by the alternation of the leaves of neighboring pairs or whorls; in such cases the number of leaves is double that at one node. Alternate leaf arrangement may be varied in the number of orthostichies (vertical files of leaves) and the magnitude of the angles of divergence between successive leaves; this is expressed by a formula of phyllotaxy that represents the fraction of the angle of divergence in segments of the circumference. Most often found are 1/2 (double-row leaf arrangement), 1/3 (three-row leaf arrangement), and 2/5 phyllotaxy; phyllotaxies of 3/8, 5/13, 8/21, etc., are less common. The denominator is the number of orthostichies; the larger it is, the less shading of leaves by one another occurs.

The regularity of leaf arrangement is due to the dimensions of the growing point and the leaf primordia and their reciprocal influence. According to one hypothesis, each leaf primordium forms a physiological field around itself that inhibits the development of new primordia in its immediate vicinity. According to another theory, the development of each succeeding leaf primordium is not inhibited but stimulated by the preceding one.

T. I. SEREBRIAKOVA

References in periodicals archive ?
Eurika 's phyllotaxy which is aired enough and condensed in Citrus sinensis, the nature of the orange tree sap and it's periods of phonology which are disadvantageous for development of this insect scale.
Several aspects of phyllotaxy and leaf development such as size determinants, polarity, and lobe formation have been studied in detail.
The new primordium subsequently acts as auxin sink, which yields a patterning mechanism for the proliferating SAM and defines the mode of phyllotaxy.
Conversion from distichous to decussate phyllotaxy could thus result from differential regulation of homologs of the ABPH1 gene in heteroblastic species.
Floral traits scored included the presence of floral organs (stamens, carpels, petals, and sepals), whorled phyllotaxy, internode compression, lack of axillary structures, and determinate growth.
The efficiency of light interception may be influenced by many factors, including branch angles (Honda and Fisher 1978, Fisher 1986) and branching patterns (Waller and Steingraeber 1985), leaf size and shape (Givnish 1984, Niklas 1989), phyllotaxy and internode lengths (Niklas 1988), leaf display and overlap (Chazdon 1985, Niklas 1988), tree inclination (Berner 1992), and overall crown shape (Horn 1971, Kuuluvainen 1992).
Convex meristems range from very sharp to rounded in shape and tend to characterize fast-growing slender stems with a loose phyllotaxy.
On the other, the basic patterns of shoot histogenesis and vascular tissue development, the control of phyllotaxy and the sites of leaf initiation are phenomena that reflect the integrated functioning of the shoot apex as a whole and may be essentially independent of cell lineages.
The available evidence indicates, however, that in at least some species of ferns there is no strict correlation between shoot apical segmentation and phyllotaxy (Hebant-Mauri, 1975, 1993).