Everyone knows the common lawn violets. Viola papillionaceae or V. cucullata. They are the state flower of New Jersey and men with pristeen lawns hate them. One reason that they are such effective weeds is their means of reproduction.

They have normal 5 petaled flowers in spring. These have infrared landing pads for bees that direct them to the nectar source which is produced in a spur in the lower petal (disect a viola or pansy flower next spring and you will easily find the spur). When the bees pollinate the flowers and seed forms it gets shot out with a sort of spring loaded slingshot effect far and wide.

As if that wasn't enough they have a second sneaky way of pollination. later in the summer they produce cleistogomous flowers way down in the foliage and almost beneath the ground. These are enclosed flowers that never open (they may have no petals or just two petals or be made up of just closed sepals). They pollinate themselves! Interesting because most flowers have very specific means to prevent self pollination so the genes spread. I believe that these seed are dropped right at the base of the plant (which is why in spring you often see your lawn violets growing in close clumps) but they may also spit some of these far away too.

I had learned of this in school but never saw it before. When I was weeding some violets out of the border I discovered this secret reproduction method. Caught in the act!

You can see on the left a flower just forming and on the right two seed pods forming. In the back you can see one that has already burst and released its seed.

Cool huh?

I am not sure how and why they evolved to do this. How does it help them? What is the benefit of self pollination when most plants try to avoid it? Does anyone know? Please let us know.

I remember reading of an Orchid that blooms underground (!). I was almost as impressed with the botanist who discovered this as I was with the plant he described.
Oops, didn't mean to get off-course...just that your post made me remember still another strange botanical marvel. josh

googled cleistogamous flowers + evolution and there is plenty of reading to do!!

The evolution of angiosperm breeding systems has lead to the development of many floral morphologies, including cleistogamy. In this dimorphic breeding system, both open (chasmogamous) and closed (cleistogamous) flowers are typically produced on the same individual. Chasmogamous flowers are primarily outcross-pollinated while cleistogamous flowers are autogamous, producing fruits through self-fertilization.
Violet species are known to exhibit high degrees of morphological diversity and hybridization ability. One exception is the stemmed yellow violet, Viola pubescens of which there are no known hybrids

AND

This famous mixed breeding system involves different morphologies of showy, cross-pollinating (chasmogamous) flowers and non-showy, permanently closed self-pollinating (cleistogamous) flowers. Evolutionary biologists and population ecologists view this mixed breeding system as a highly successful strategy for producing genetically diverse new plants from chasmogamous flowers and other new plants very similar to the parental genotypes from cleistogamous flowers. The mixed breeding system is found in many distantly related plant families and has recently been proposed as a vehicle for containment of transgenic modifications in plant groups where it could be induced. However, the molecular mechanisms underlying this fascinating system have never been investigated.

Is there any known way to encourage the growth of chasmogamous flowers on a plant that only seems to produce cleistogamous flowers? I grow the violets as food for caterpillars, but I do like the flowers and wouldn't mind seeing them occasionally. Or is it possible that mine have become sufficently inbred that they can't produce chasmogamous flowers?

BP

BP