User Contributed Dictionary
Pronunciation
IPA: /fɪlə'tæksɪs/Noun
phyllotaxis
 the arrangement of leaves on a stem, or the mathematical principles governing such arrangement

 1985: Yet his Lordship would find this rate of proportion (…) likewise in all plants, in the disposition of their leaves, for which ordering he would make a name, that is, from the Greek, phyllotaxis. — John Fowles, A Maggot
Extensive Definition
In botany, phyllotaxis or phyllotaxy
is the arrangement of the leaves on the stem of a
plant. The basic
patterns are alternate, opposite, whorled or spiral. With an
alternate pattern, leaves switch from side to side. An alternate
distichous
phyllotaxis means that each leaf growing at a single node is
disposed in a single rank along the branch (such as in grasses). In
an opposite pattern, two leaves grow in opposite directions from
the same node. In an
opposite pattern, if successive leaf pairs are perpendicular, this
is called decussate. A
whorled pattern consists of three or more leaves at each node. An
opposite leaf pair can be thought of as a whorl of two leaves. A
whorl can occur as a
basal structure where all the leaves are attached at the base
of the shoot and the internodes
are small or nonexistent. A basal whorl with a large number of
leaves spread out in a circle is called a rosette. A multijugate pattern is a
spriral composed of whorls. The pattern has also been observed to
emerge in at least one animal cell (the red blood cell), during
processes that perturb cellular fluid dynamics .
Insight into the mechanism had to wait until
Wilhelm
Hofmeister proprosed a model in 1868. The process begins with
two primordia, nascent
leaves, forming on opposite sides of the shoot. A third new leaf
then erupts between them. Each old leaf pushes the upstart away.
The golden angle
is the blind result of this jostling. Since three golden arcs add
up to slightly more than enough to wrap a circle, one of the old
leaves overlaps and is pushed out in a radial line, like a rocket
that escapes earth orbit. This vacates space in the inner generative
spiral for a new leaf to form. The generative spiral should not
be confused with the clockwise and counterclockwise spirals that
emerge in densely packed plant structures. Spirals are discerned by
tracing the path from leaf to neighboring leaf and each leaf
acquires new neighbors as it shoots out from the center and its
sister primordia. New leaves move into the spaces opened as old
leaves diverge. Phi is an irrational
number and this guarantees that no two leaves ever follow the
same radial line from center to edge. In modern times, researchers
such as Snow and Snow have continued these lines of inquiry.
Computer modeling and morphological studies have confirmed and
refined Hoffmeister's ideas. Questions remain about the details.
Botanists are divided on whether the control of leaf migration
depends on chemical gradients among the primordia
or purely mechanical forces. Lucas
rather than Fibonacci numbers have been observed in a few plants
and occasionally the leaf positioning appears to be random.
References
 F.M.J. van der Linden
 Frank M.J. van der Linden: Creating Phyllotaxis, The StackandDrag model, in Mathematical Biosciences, NY 1996
 Frank M.J. van der Linden: Creating Phyllotaxis from Seed to Flower, in Symmetry in Plants, Jean & Barabé eds., World Scientific, Singapore 1998
See also
External links
 Fibonacci Numbers and the Golden Section
 Spiral Phyllotaxis Pattern in an Animal Cell: A Fluid Driven Mechanism for Red Cell Echinocytosis and Programmed Cell Death a paper by Dr. Juanita Lofthouse presenting the first example of an animal cell exhibiting Phyllotaxis patterns in response to changes in cell metabolic rate and other dynamic perturbations
 Phyllotaxis as a Dynamical Self Organizing Process
 Phyllotaxis Spirals and Phyllotaxis Spirals in 3D by Stephen Wolfram, The Wolfram Demonstrations Project.
 Phyllotaxis: An Interactive Site for the Study of Plant Pattern Formation
 PhaseLab
phyllotaxis in German: Phyllotaxis
phyllotaxis in Spanish: Filotaxis
phyllotaxis in French: Phyllotaxie
phyllotaxis in Korean: 잎차례
phyllotaxis in Hungarian: Levélállás
phyllotaxis in Dutch:
Phyllotaxis