clarification of phyllotaxis

Patrick Elvander elvander at biology.ucsc.edu
Fri Nov 21 11:50:53 EST 1997


On 20 Nov 1997, Grant R. Cramer wrote:

>  I am hoping one of you can enlighten an ignorant soul. I have been
> teaching my class about phyllotaxis using  the text "Botany' by Moore et
> al. They define phyllotaxis as the number of turns of a spiral/number of
> leaves BETWEEN successive leaves of an orthostichy. As I went to expand on
> this subject by giving an example from Esau's "Anatomy of Seed Plants", I
> discovered that she describes 5/13 phyllotaxy as "five windings about the
> axis include 13 leaves with leaves n and n plus 13 located one above the
> other". That is there are only 12 leaves BETWEEN successive leaves of the
> orthostichy. These two definitions are slightly different but important.
> The other surprise was that the phyllotaxis was 5/13 not 8/13, which is
> what I expected based on the Fibonacci series and how it is explained in
> Moore et al.
> 
> My question is "What is the correct definition of phyllotaxis" or is there
> no agreement on this?

OK, I teach Plant Anatomy so let me see if I can shed some additional
light here:

Phyllotaxy is simply defined as the arrangement of leaves on the stem; it
is, thus, a very general term. There are two main types of phyllotaxy:

Orthostichy, in which the leaves are arranged in vertical lines on the
stem (leaves whorled or two opposite each other at a node are examples) 
and

Parastichy, in which the leaves are arranged in a helical pattern on the
stem. Parastichies only can be described by the Fibonnaci series cited
above. The 5/13 arrangement referred to above indicates that, beginning
with one leaf at a node, after 5 turns of the genetic spiral helix (in
which you count each successivley produced leaf in order) you will find
yourself 13 NODES down the stem at a leaf which is directly below the leaf
you started with (Note: you don't count the leaves in between the two
nodes, you count the nodes with number one being the next node down from
the one you begin with and the last node counted is the one you stop on).
The parastichous Fibonnaci sequence begins with 1/3,
then goes to 2/5, 3/8, 5/13, 8/21, etc. As you can see, this follows the
Fibonnaci series in the denominator and independently in the numerator.

Hope this helps and that I've explained it clearly.

_________________________________________________________
	Patrick Elvander	Department of Biology
	Lecturer in Biology	Sinsheimer Labs
	408-459-3674		University of California
				1156 High St.
elvander at biology.ucsc.edu	Santa Cruz, CA  95064
_________________________________________________________




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