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From: Susanne Renner <Renner at UMSL.EDU>
Subject: Arisaema sexual strategies
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Jim McClements wrote:

>By a "non-sex changer" I assume that you mean that the adult plants are
>monoecious, containing both male and female flowers. That has been the
>conventional view of the species, as far as I know.

Dear Jim,

By 'sex-changer' I mean that a plant start its reproductive life as=a
male, but become a simultaneous male and female or a pure female later on.
This is a common sexual strategy in animals, but rare among flowering
plants.  In Araceae, it is only known from Arisaema.  The evolution of
sexual strategies in Arisaema is one of the topics we are hoping to study
in the context of our phylogeny for the genus.

Although Arisaema sexual strategies are not clear-cut, they have been
classified as follows:

Strategy A involves the production of only male inflorescences at an earl=y
stage, followed by production of bisexual spadices at a later stage.

Strategy B involves sequential male, bisexual, and female life stages.
Examples: A. flavum, A. tortuosum,  A. candidissimum?? This strategy is
poorly separated from A  and is perhaps an artefact.

Strategy C involves abrupt inter-annual change from male to female. At
least 8 spp. follow strategy C:

A. dracontium from North America,
A. macrospathum from Mexico,
A. filiforme from Java,
A. grapsospadix from Taiwan,
A. prazeri from India and the Himalayas,
A. somalensis from Somalia,
A. tortuosum from India and China, and
A. wrayi from India


Regarding your question about the names of the subspecies of A. flavum: I
need to check Murata's paper again:
Murata, J. 1990. Three subspecies of Arisaema flavum (Forssk.) Schott
(Araceae). J. Jap. Bot. 65: 65-73.


>With regard to the "selfing" question, isn't any monoecious species capa=ble
>of this, at least in theory?

No.  Most bisexually-flowered angiosperms and most unisexually-flowered
monoecious angiosperms have a genetic mechanism called
self-incompatibility, which prevents self-pollen from germinating (either
on the stigma or inside the style, depending on the particular type of
self-incompatibility).

>I can't swear to it, but i think I've seen A.
>tortuosum, which is monoecious, self-pollinate.

If you can confirm this observation, it should be published.  It would be=a
neat addition to our understanding of Arisaema mating systems.  There are
very few experiments that have tested whether or not aroids set fertile
seeds after self-pollination.  As you say, species that normally are
single-sexed sometimes have flowers of both sexes on
the spadix while making the transition from male to female. Whether or no=t
they can self during this period needs to be experimentally investigated.
My gut feeling is that probably they can.

>[selfing wouldn't work if] flowers shed their pollen before the female
>stigmata are receptive, but some overlap can >probably occur.

Overlap definitely occurs in the selfing subspecies of A. flavum.  This h=as
been demonstrated by
Vogel. S., and J. Martens. 2000. A survey of the function of the lethal
kettle traps of Arisaema (Araceae), with records of pollinating fungus
gnats from Nepal. Bot. J. Linn. Soc. 133: 61-100.

Susanne Renner