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  Lemna and other duckweeds
From: "Eduardo Goncalves" edggon at hotmail.com> on 2000.06.20 at 18:45:33(4863)
Dear Aroiders,

Since I received some private messages concerning my last not-so-funny
joke, I think I should present this aspect to the whole list. Some say they
are shooked-up about the fact that Amorphophallus and Lemna being close
relatives. Others corrected me, saying that Lemna is a genus of Lemnaceae
(duckweed family), not an aroid. Ok, I have a bombastic new to the members
that have been sleeping for the last five years. Yes, all duckweeds are true
aroids! In fact, duckweeds can be better considered like an aroid than
Gymnostachys, Orontium and Symplocarpus! I will try to explain it (before
you try to beat me)...
Taxonomy has suffered an irreversible micro-revolution in recent
years. Since Linnean times, taxonomy deals exclusively with morphological
aspects like shape of organs, color, etc. The taxonomic dataset has been
improved by plant anatomy (or micro-morphology), chromosomic features and
phytochemistry, but all of this aspects concern phenotypic information.
After the discovery of the structure of the DNA by Watson & Crick, we became
able to take a closer look to the essence of the living beings, i.e. we can
'read' their genes. It is true that it is not so simple to access and
compare genes, but it is potencially a very powerful tool.
Lemnaceae has been considered a "good" family for much time, since
they are all free floating plants, with similar reduced flowers. Until very
recently, most taxonomic treatments include Lemnaceae as a distinct family,
always based on phenotypic features. If I am not confused, in the book
"Families of Monocotyledons", R. Dahlgren and colleagues included Lemnaceae
in the order Arales, together with Araceae.
In French's work (with collaborators) concerning the cladistic
analysis of restriction site changes in Araceae, the genus Lemna was
included. Interestly, it appeared well nested within the "advanced" aroid
genera, being closer to a "twig" that includes Amorphophallus, all
Caladieae, all Areae and all Colocasieae. Just for information, the "twig"
with Gymnostachys, Orontium and Symplocarpus ("Proto-Aroids") are very far
from it, and seems to be almost as a syster family. The same you can see if
you analyse the sequence of the genetic marker rbcL. These data with rbcL
were not published, but I used the sequences I imported from GenBank, just
for fun. I surveyed Lemna and Spirodela (both from the Lemnaceae) and both
appeared like "advanced" aroids. Once again, the Proto-Aroids appeared so
related to the other aroids as a Potamogeton I used in this analysis! This
is to show you that if you put Lemnaceae as a distinct family, you should
also separate Gymnostachys, Orontium and Symplocarpus in a distinct family,
and probably a miriad of other "small families". I don't think it would be a
good idea, since I love aroids with all currently recognized genera!
I know that Lemna and all the other genera in Lemnaceae don't look
exactly like an aroid. They are a very specialized group of free-floating
plants, with very fast vegetative reproduction. The reduction in their
reproductive organs (maybe because big flowers make small plants to sink in
the water) seems to be strongly adaptative, and resulted in the poor
recognition of these plants like true aroids. However, we can't say that
they are not aroids only because WE couldn't recognize them before! If we
want a taxonomy based on the evolutive history, I think we should consider
those diminute duckweeds like true aroids, just like we recognize an
outrageous A. titanum! Ok, who will be the fist one to shoot me?

Best wishes,


From: "Peter Boyce" p.boyce at rbgkew.org.uk> on 2000.06.21 at 17:36:02(4876)



From: "Gabe Thomas" CDANIELLE at prodigy.net> on 2000.06.21 at 17:37:45(4877)
All this time I thought I didn't have anything I could trade to fellow aroid
enthusiasts and it turns out I have millions of little aroids floating
around in my water gardens... Duckweed anyone?

Gabe Thomas

From: Lewandjim at aol.com on 2000.06.21 at 17:39:18(4878)
In a message dated 06/20/2000 9:46:06 PM Eastern Daylight Time,
edggon@hotmail.com writes:

<< Since I received some private messages concerning my last not-so-funny

From: StellrJ at aol.com on 2000.06.21 at 17:45:59(4882)
In a message dated Tue, 20 Jun 2000 9:46:08 PM Eastern Daylight Time,
"Eduardo Goncalves" writes:

<< Dear Aroiders,

From: "Eduardo Goncalves" edggon at hotmail.com> on 2000.06.21 at 19:39:02(4885)
Dear Jim,

Yes, you're correct. Let me try to say it with more precison: If you
consider that all taxa are a somewhat stable assembly of genes that were
transfered mainly in a "vertical" way in recent times, the best hypotesis we
have now for the duckweeds is that they are very specialized forms of the
assembly of genes we use to call aroids. They share very similar sequence of
cpDNA genes we suppose that are homologous and they are also very similar if
we compare the effect of restriction enzimes at the total DNA (nuclear +
plastid). Since we don't know any other thing that could be considered
better than DNA to show relationship without "morphogenetic black boxes",
all this evidence make us believe that aroids+duckweeds can be considered a
good taxonomic group together. I know there are lots of strong limitations
(like reticulation, lost genetic information, possibility of "lamarckist
genes", horizontal transference, etc), but I think it is the best
information we have. Maybe, in the future, we will be able to travel back in
the time and see different stages of evolution of the Araceae. Maybe we will
discover that we will never now the true story of evolution (because it is
unique and most evidences are lost) so the taxonomy will be deliberately
artificial! (Hey, that will be really good... For the first time after
Darwin's era, we will be able to be sure about our taxonomic concepts). Ok,
I think I can't be more precise than this by now. I still can refine my
concepts, but my poor English is already lacking! Maybe if I could write in
Portuguese... :o)

From: DeniBown at aol.com on 2000.06.22 at 15:36:26(4888)
Phew! Now I know no one is going to get shot at, I'll come out from under
the bed and say that in the revised edition of Aroids - Plants of the Arum
Family (to be published in September) I treat duckweeds as aroids and explain
(in layperson's terms but with scientific references) the whys and wherefores
of this fascinating taxonomic change. Thank you, Eduardo, for risking life
and limb in giving us your lucid comments on the subject.

I have always thought that the Araceae is the most mind-boggling family of
plants on this planet, and now that it embraces the gigantic Amorphophallus
titanum and miniscule Wolffia microscopica, no one can question it - unless
to wonder if they are from another planet after all!

Deni Bown (lurker)

From: Aroideae at aol.com on 2000.06.23 at 16:47:34(4897)
I'm another one who very much enjoyed eduardo's very informative posting!
i'm hungry for more. now, I cannot resist asking!! What is Wolffia

From: Dean Sliger deanslgr at juno.com> on 2000.06.23 at 20:23:45(4901)
On Fri, 23 Jun 2000 18:47:34 -0500 (CDT) Aroideae@aol.com writes:
> I'm another one who very much enjoyed eduardo's very informative
> posting!
From: Aroideae at aol.com on 2000.06.24 at 17:27:46(4908)

thankyou for the information! aroids are amazing! no wonder we're 'hooked'.


From: StellrJ at aol.com on 2000.07.07 at 16:42:34(5007)
In a message dated 6/23/00 11:24:17 PM Eastern Daylight Time,
deanslgr@juno.com writes:

<< I've carefully

From: Lewandjim at aol.com on 2000.07.07 at 19:38:36(5014)
In a message dated 07/07/2000 8:00:11 PM Eastern Daylight Time,
StellrJ@aol.com writes:

<< << I've carefully

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