On Wed, 17 Mar 2004 15:57:11 +0000 (UTC), schuetz-kemmern{at}t-online.de
(Daniel Sch?tz) wrote:

>Dear NG,
>
>in zoology there are a lot of evolution models for the origin of
>multicellularity. But is there any model for the origin of
>multicellularity in botany, too? What? How does it think about? I've
>you do know, please contact me or write in this NG.
>
All models of multicellularity stem from models in the Protista.
There are numerous algae (brown, red, and green) with true
multicellularity.  In particular, the green algae represent the origin
of the multicellular plants (they share chlorophyll-b, cellulose cell
walls, starch storage).  The charophyceans in particular seem to be
the origin of the plants.

Green algae include single celled forms, forms made of two cells or
small clumps of cells, long filaments, sheets, and globular clusters.
Look up the "Volvocine series" in google for examples of what is
traditionally considered one model for the evolution of
multicellularity.  Check out 

  Kirk D. (1999) 
  "Evolution of multicellularity in the volvocine algae", 
   Current Opinion in Plant Biology, 2 : 496-501

Abstract: Recent studies reveal that relationships among the volvocine
algae are more complex than was previously believed. Nevertheless,
this group still appears to provide an unrivaled opportunity to
analyze an evolutionary pathway leading from unicellularity
(Chlamydomonas) to multicellularity with division of labor (Volvox).
Significant progress in this regard was made in the past year when two
genes playing key roles in Volvox cellular differentiation were
cloned, and clues were uncovered regarding their mechanisms of action.

I can't find a free copy of this on the web.

For some general thoughts on the subject, not restricted to plants,
see 

PNAS paper by Pfieffer and Bonhoeffer, "An evolutionary scenario for
the transition to undifferentiated multicellularity" at 
http://genetics.med.harvard.edu/~dsegre/Pfeiffer_Bonhoeffer_PNAS_2003_multicell.pdf

Heredity paper by Michod and Roze, "Cooperation and conflict in the
evolution of multicellularity" at
http://eebweb.arizona.edu/Michod/Downloads/Cooperation%20and%20conflict%20Heredity%20paper.pdf
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