----- Original Message -----
To: Multiple recipients of list AROID-L
Sent: Tuesday, June 20, 2000 6:48 PM
Subject: Lemna and other duckweeds
> 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,
>
> Eduardo.
>
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