From: "Julius Boos" ju-bo at msn.com> on 2003.05.18 at 12:27:50(10266)|
Dear Zack, Marc and Friends,
I have a couple observations and comments on this subject-- in Urospatha
the female and then the male anthesis are very obvious (as I noted in my
notes on this genus in Aroideana), the female anthesis takes place just as
the spathe begins to open, and drops of liquid will be observed on the
stigmas. This phase lasts several days, then the tips of the stigmas turn
brown and dry up. Soon after the female phase is completed, the strands of pollen can then be observed being produced, starting
at the very TOP of the spadix and slowly working downward the entire length, and
this phase can take a week to ten days or more. Because these two phases take place
pretty far apart and with no apparent 'overlap', and the female stigmas are dry when the pollen is being
shed, I do not believe self-pollination can take place. But---on a large
mature plant just a very few fruit will still develop and contain some viable
seed without apparent pollination , even if there is only one bloom on a single plant in your collection. Small or immature plants will generally abort the bloom with no fruit/seed production, and (as I have suggested previously) perhaps only make their contribution to genitic diversity by their pollen production. I discussed this with the late Dr. Birdsey, he explained that this seed production without pollination is called 'apomixis', and is not self-pollination. Recently I have seen a Xanthosoma acutum
Goncalves (section Acontias, a tuberous sp. like most Caladium sps.) develop
a full infructesence with only one bloom present, and since this genus also
has distinct non-overlapping (as far as we know) female then male anthesis, we suspect apomixis in at least this species in the genus Xanthosoma.
I have been pondering the possible 'benefit' of apomixis vs. true self-pollination, and wonder if my thoughts bear merit---we are told that self-pollination is not a 'good' thing because of the non-transference of genetic material between two different plants, so we accept this, and so I wonder how apomixis may 'benefit' a plant. I was thinking----suppose a single seed, transported by a bird or other means, falls on fertile ground and grows into an adult and flowering plant, but too far removed from another plant or population to allow for cross-pollination. The plant blooms, and a few seed are produced by apomixis which fall and grow near to the single parent plant, these plants are clones of the 'mother' plant, but we should bear in mind that in her seed she carries the genes of her parents and the plants that produced 'her'. When a bloom from this population of clones is pollinated by another related clone, there is more mixing of genetic material than would occur if there were true self-pollin
ation (but less than if there were cross-pollination by an unrelated plant), so eventually this may allow this population that were originally clones by apomixis to become a self-sustaining and sufficiently diverse in genetic material to be healthy population, as soon there will be sufficient plants in this new population to allow cross pollination to begin.
> Aroids is a big family with great variability.
> Due to the protogyny, self-pollination is not supposed to be common (but
> several taxa have overlapping stigma receptivity and pollen release).
> Arisarum vulgare can be self-pollinated, if you brush the stigma with a
> For example in Arum, you can not self-pollinated within a same
> inflorescence but in many cases you can "self"-pollinated between
> inflorescences of a same individuals (that is called geitonogamy).
> Do you have some genera in mind?
> All the best,