Crinum With Unusual Foliage
Johnson3591@aol.com (Tue, 30 Dec 2003 06:53:36 PST)

In a message dated 12/30/2003 2:13:09 AM Central Standard Time,
mrgoldbear@yahoo.com writes:

Hi,

If you stop to think about it, the arrangement of leaves directs the entire
structural design of a plant. This is because placement of leaves also directs
placement of buds and hence branching. The arrangement of leaves is called
phyllotaxy. Leaves may be alternate, opposite, decussate or distichous; maybe
there are other arrangements.

Determination of leaf placement occurs at the apical meristem; phyllotaxy is
often described as "whorled" or "spiral." Leaf primordia arise at the shoot
meristem; the primordia are little bumps of cells that will become leaves.
Generation of leaves may involve the entire node circumference of the meristem
(whorled). In spiral arrangement only part of the meristem (one side) is
involved in creating the leaves; in spiral arrangements the next primordium is
separated from the previous by an angle of about 137 degrees.

In whorled arrangements 1 primordium may be produced per node leading to
alternate leaves (dogwood); or 2 primordia may be produced on opposite sides of
the giving rise to distichous phyllotaxy (like corn) or decussate phyllotaxy
(like some Crassula species).

Spiral phyllotaxy is common; if you do the math (137 degrees separating each
leaf) you can see that 8 leaves are produced for every 3 full turns around the
stem, or that 13 leaves are possible every 5 full turns around the stem etc.
(Fibonacci series).

If spirally arranged leaves are telescoped very close together along a stem,
you can get what you see in most Crinum, an apparent whorl of leaves going
every which way. If spirally placed leaves are separated by inches you get a
typical branch (like a rose bush).

Anyway, not much is known about the regulation and control behind leaf
primordia formation. But genetic studies have indicated that a single gene or two
can make a lot of difference.

LINK 1: Distichous Leaves, Aloe plicatilis
http://halstedgallery.com/artists/i_cunningham/…
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LINK 2: Decussate Leaves, Crassula hybrid
http://rth.org/occss/1998show/…

LINK 3: Phyllotaxy Drawings and Essay
http://ct-botanical-society.org/newsletter/…

Cordially,