No subject

[Arisaema Enthusiast Group (AEG) Discussion List (and other=]

hardy  Aroids)" <ARISAEMA-L at NIC.SURFNET.NL> Aroids)" <ARISAEMA-L at NIC.SURFNET.NL>
Sender: "Arisaema Enthusiast Group (AEG) Discussion List (and other=
From: Susanne Renner <Renner at UMSL.EDU>
Subject: still: Arisaema sexual strategies
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

Pascal,

The classification of Arisaema sexual systems into three types
isn't mine but was proposed by Hotta (1971, p. 286), and problems with th=is
categorization have been pointed out repeatedly, most recently by
Richardson & Clay (Plant Species Biology 16: 1-11, 2001 ).  As you say,
observational data from cultivated plants are difficult to interpret, and
field observations have been published for only 15-20 of species (dependi=ng
on one's definition of "field").
The terms dioecious and paradioecious do not apply to Arisaema (i=n
spite of their occasional use by Arisaema workers).  Dioecy is the sexual
system where each individual is either genetically male or female and thu=s
incapable of producing gametes of the other sex.  Paradioecious species a=re
(evolutionarily) on the way to dioecy, with mostly male and female plants=,
but a few genetically inconsistant individuals.
All arisamea are genetically bisexual and capable of producing ma=le
and female gametes, albeit usually in different years.  Arisaema is
therefore neither dioecious nor paradioecious.  Gender choice as practise=d
by Arisaema is something very special: You reap the ecological benefit of
outcrossing while not suffering the reproductive cost of giving up one
sexual function for good (the way dioecists do).   As far as known, 8-10 =of
the c. 13400 genera of flowering plants are capable of sex change (gender
choice).


>Producing only male/female flowers is the best
>way to ensure that self-pollination does not occur.

Yep.  However, other aroids manage to achieve the same effect by less
striking temporal separation of male and female function.  If it's enough
to separate pollen release and stigma receptivity by days or hours, why
separate by years?  Are arisaemas living under such stressed conditions
that they can't afford to be female most years?

>..  [Arisaema] flavum is generally regarded as one of the most primitive
>species so maybe flavum ssp. tibeticum is the most primitive of all the
>Arisaema?

In our molecular phylogenetic tree for the genus, A. flavum does not plac=e
as an early offshoot (I do not want to use the term primitive); rather it
appears relatively derived.  However, we need to sequence a longer stretc=h
of DNA to be sure.

Susanne