 The flower is the most beautiful part of a plant, but it's not just the beauty of a flower that is so interesting about it. The flower is actually a very complex organ. It is as you know the reproductive organ of a plant and it has all these different worlds, the calyx, the corolla, the androsium, and the gynotium, all of which play a very important part in reproduction. All these different parts of the flower rest on this basal structure called the thalamus. The way in which all these parts, the sepals, the petals, the stamens, and the carpals are arranged on the thalamus may be symmetrical or asymmetrical. When the arrangement is symmetric, the flower can be of two types, actinomorphic and zygomorphic. What is actinomorphic? There is a radial symmetry in the flower. So what do I mean by radial symmetry? There is more than one plane which can divide the flower into two equal parts. So actinomorphic has radial symmetry and there are more than one planes which can divide the flower into two equal parts, like this. So this is one plane, this is another plane, this is another plane, and so on. There are five planes like this. I have drawn lines here, but if you imagine three dimensionally, then actually these are planes that are cutting the flower. So there are five such planes in this case, which can cut the flower in a way that we can divide the flower into two equal halves. So that's radial symmetry and the flowers which have radial symmetry are called actinomorphic. Actinophthno actually means ray. So when you draw all these lines that divide the flower into halves, they look like rays, hence actinomorphic. So that's one type of symmetry present in flowers. The other type is zygomorphic in which there is just one plane which can divide the flower into two equal halves. So right here. This is the only plane that can divide the flower into two equal halves and this is called bilateral symmetry. So an example of bilateral symmetry flowers would be flowers belonging to the family of peas and then for radial symmetry, as you can see, hibiscus is a good example. So these are the symmetric flowers. Now there are some flowers which are asymmetric. You can't think of any possible plane for this flower which will divide it into two equal halves. The flower over here is called canna. This is only one way in which the flower can be classified. There are other ways too. Another way of classifying the flower is mirosity. What is mirosity? It is the number of the parts of a flower like the number of petals, number of sepals, or the number of statements. So most of the flowers are either trimaris, tetramerus, or pentamerus. What do I mean by that? In trimaris flowers, the number of parts of a wall of a flower is three or multiples of three. For example, in this flower, you can see there are six petals. So six is a multiple of three. So this is a trimaris flower. Similarly in tetramerus flowers, the parts of the different walls are either four or multiples of four. Like in these flowers, there are four petals. In pentamerus flowers, as you must have guessed, the number is five or a multiple of five. In this case, the number of petals is ten. So this is another way of classifying flowers. Another way of classifying the flower is the presence or absence of bracts. So what do I mean by bracts? So a bract is a leaf or a modified leaf that is present at the base of the stalk of a flower. So right here is the flower and this is the stalk also called the pedicel and then at the base of the pedicel is this leaf which is called the bract. So this flower is bractiate. Because it has a bract and flowers which do not have bracts are called a bractiate. So right here, if you look closely, these are the pedicels of the flowers and there is no leaf or leaf-like structure at the base of any of the pedicels. Hence, these flowers are a bractiate. Finally, we are going to look at the classification of the flower in terms of the position of its ovary with respect to the rest of the parts of the flower. So in some flowers, the ovary is present above the rest of the walls. So these are the sepals, these are the petals, these are the stamens and this is the ovary. As you can see, the ovary is at a higher level than all of the others. So this is said to have a superior ovary, superior because it is above the rest and the flower is said to be hypogynous. Hypomens below and gyness, gyno means female. So the rest of the parts of the flower are below the ovary, hypogynous below ovary. Hence, this flower is said to be hypogynous. The opposite of this is epigynous in which the ovary is below the rest of the parts of the flower. If you see here closely, the ovary right here is below all of these other things, the sepals, petals and stamens. This kind of an ovary is said to be inferior ovary and the flower is said to be epigynous. Epi means above. So the rest of the parts of the flower are above the ovary. Hence epigynous. Now there is a type of flower which has the ovary in between, neither quite superior nor quite inferior. So it's something like this. As you can see, the other parts of the flower are kind of in between, not quite above the ovary, not quite below the ovary and this is said to be half inferior ovary. And the flower is said to be perigynous and perigynous means what? Peri means around or about or beside. So the other parts of the flower are kind of beside or around the ovary, hence the name perigynous. So why are we studying all this? Why are we looking at all the different ways in which a flower can be classified? Because this is a good way to differentiate between the flowers of different families. Just as we classify animals, we need to classify plants as well and in angiosperms a very easy way of classifying plants is to look at the flowers, the differences between them. So one way of differentiating flowers is this, looking at the different arrangements of the different parts of the flower in general. And then we also look at specific arrangements, how the petals are arranged with respect to each other, how the stamens are arranged, how the ovaries, the ovules are arranged. We classify flowers based on those as well and we will look at all that in subsequent videos.