My understanding is that what matters in distinguishing members of the plant
kingdom (embryophytes) from the macrophytic algae is not that they have
embryos,
but that the embryos are protected, a very useful characteristic for
organisms
on dry land. Specifically, fertilization takes place inside an archegonium
and/or ovule, and the zygote develops into an embryo right there, within the
protection of the archegonium/ovule. The green algae thought to be closest
to
the plant kingdom (e.g. Chara, Coleochaete)have internal fertilization, but
the
zygote does meiosis right away -- no 2n embryo to be protected. Other algae
with lovely 2n embryos (e.g. Fucus)produce them from zygotes formed by
external
fertilization, so there's no automatic protection.
On the kingdom question.... Although grouping embryophytes and charophytes
together seems straightforward, I think there's some evidence that the green
algae
as a whole are polyphyletic. Of course, their chloroplasts may be more
closely
related than their nuclei.
_____________________________
Dr. Katherine M. Schmid
Dept. of Biological Sciences
Butler University
4600 Sunset Ave.
Indianapolis IN 46208
317-940-9956
kschmid at butler.edu
