Gynoecology PBIO 381 Fall 2009
Flowers Q. In the slide show it says that if all four whorls are present, then the flower is complete and perfect. I thought whorls referred to whorled leaves, but here it means calyx, corolla, sepals, petals?
Gynoecium Androecium These are the four whorls of the flower
A flower that has all four whorls is said to be both complete and perfect.
Q. Is there any physiological difference between sepals and petals, aside from the fact that sepals tend to be photosynthetic? Are they different on a cellular or developmental level?
On Carpels and Pistils Gynoecium
Q. Is there more to the gynoecium than the pistil? Are they synonymous? Q. Pistil and carpel, what’s the difference? The gynoecium is the female part of the flower, the pistil or pistils. (Some flowers have more than one. ) The pistil comprises the ovary, the style, and the stigma.
Q. But then what is a carpel? A. It’s the female part of the flower, comprising the ovary, the style, and the stigma. But you said that was a pistil … Ah: if each pistil is made up of but one carpel, then the carpel and the pistil are the same. The pistil is said to be simple.
However, a compound pistil is made up of two or more fused carpels.
Q. One of the slides suggests that pistils developed from sporangia. Is this how it happened, evolutionarily?
The carpel was derived in the course of evolution from a sporangium-bearing leaf Simple pistil e. g. , pea Compound pistil e. g. , green pepper
Q. Does each carpel have its own pollen tube? Q. Can each carpel potentially be pollinated by a different males' pollen? Each individual ovule must be pollinated by its own pollen grain! Each can be pollinated by a different pollen parent.
Q. Could a flower have multiple compound pistils?
A. No: there are only three possibilities for gynoecium structure: • One simple pistil per flower (e. g. , pea) • Two or more simple pistils per flower (e. g. , buttercup, arrowhead) • One compound pistil per flower (e. g. , cucumber, tomato)
One simple pistil per flower. . .
Two or more simple pistils per flower. . .
One compound pistil per flower
Q. How do locules and carpels differ? Is it dependent on the placentation and the chamber walls?
Placentation
Q. In one of the pictures there is a pistil with only one chamber, but it seems to be labeled as a compound pistil. Is that because there are multiple clusters of ovules? Q. Does free central placentation always mean simple pistils? A. Yes - in the case of free-central or parietal placentation, There is but one locule though there are multiple carpels.
How to determine the number of carpels in a compound pistil? • If the placentation is axile, count the number of locules (chambers) in the ovary • If the placentation is parietal, count the number of placentae
How to determine the number of carpels in a compound pistil? • If the pistil has more than one style and/or stigma, count them • If the fruit is dehiscent (opens up), count the number of seams
Ovary Position
Q. How do you distinguish between superior and inferior ovaries when you are looking at the flowers of unfamiliar plants?
A. It’s often helpful to make a long section of the flower, which reveals the relationship of the ovary to the other whorls.
Q. My zucchini plant grows zucchinis below the flower petals, so that means the ovary is inferior? A. YES!
Hypanthium
Hypanthium - A floral cup or tube formed by the fusion of the basal portions of the sepals, petals, and stamens, and from which the rest of the floral parts arise.
Pistils
Q. Are there hypanthia where the ovary is fused to the hypanthium? A. Yes - in fact, that’s what’s going on with inferior ovaries.
Q. How are the hypanthium and the receptacle different? hypanthium receptacle
Complicating the issue is the fact that in some groups of plants, the hypanthium is formed from the receptacle. In Carolina allspice, for example, the hypanthium is receptacular.
Fruits
I would like to better understand how the parts of the ovary correspond to parts of the developed fruit.
Following pollination and fertilization, the ovary ripens into the fruit and the ovules mature into the seeds. Pericarp is a term for the fruit wall.
Q. Would it be possible to spend a portion of a class going over the differences between all the different fruiting types? A. Yes … or a lot of them, anyway.
True Fruits A true fruit develops from a single ovary of a single flower.
Kinds of true fruits: Fleshy Usually these are indehiscent (which is to say they don’t open up to release their seeds)
Berry: the entire pericarp is soft
Drupe: The pericarp is divided into three layers exocarp (skin) mesocarp (flesh) endocarp (stone)
Kinds of true fruits: Dry (these may be dehiscent or not )
Q. If a capsule is a dehiscent structure con taining two or more carpels, what is it called if it is just one carpel (but still many seeds)?
Follicle - a dry fruit from a simple pistil that splits open to release its seeds (it’s dehiscent).
Capsule: a dry, dehiscent fruit from a compound pistil
septicidal capsule of Aristilochia loculicidal capsule of violet (Viola)
A schizocarp splits into separate units that are dispersed separately. (These units are themselves indehiscent, and are called mericarps. )
Q. What is the difference between a samara and a schizocarp? Q. Maples have schizocarps, and I've heard it said that each one is made of two samaras. Is this correct? Because I don't buy it. A. I don’t either, but the point is almost semantic - stand by for a discussion of samaras!
An achene is a dry, indehiscent, oneseeded fruit.
A caryopsis - or grain - is like an achene except that the pericarp is fused to the seed.
A samara is a winged achene.
False Fruits A false fruit does not develop from a single ovary of a single flower.
Q. Could you please explain the parts of a strawberry? Why is the flesh considered receptacle? The strawberry is an accessory fruit: the sweet, juicy part is receptacle, not ovary wall!
A raspberry is an aggregate fruit: each little “unit” is the product of a separate ovary.
A pome is a false fruit in which the juicy edible part is hypanthium. What part of the apple is true fruit?
The pineapple is an example of a multiple fruit: the fruit is derived from the fusion of an entire inflorescence.
Q. Do the supermarket terms of 'vegetable' and 'fruit' mean much to botanist? Why or why not?
Fruit Structure is determined by two things: 1. The structure of the pistil(s) from which it formed. 2. Adaptations for dispersal of the fruit and the seeds.
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