Factors influencing floral diversity

There is enormous variation in the developmental programs of plants. For example, grasses possess unique floral structures. The carpels and stamens are surrounded by scale-like lodicules and two bracts the lemma and the palea. Genetic evidence and morphology suggest that lodicules are homologous to eudicot petals.[97] The palea and lemma may be homologous to sepals in other groups, or may be unique grass structures. The genetic evidence is not clear. Variation in floral structure is typically due to slight changes in the MADS-box genes and their expression pattern. Another example is that of Linaria vulgaris, which has two kinds of flower symmetries-radial and bilateral. These symmetries are due to epigenetic changes in just one gene called CYCLOIDEA.[98] Large number of petals in roses is the result of human selection Arabidopsis thaliana has a gene called AGAMOUS that plays an important role in defining how many petals and sepals and other organs are generated. Mutations in this gene give rise to the floral meristem obtaining an indeterminate fate, and many floral organs keep on getting produced. Roses, carnations and morning glory, for example, that have very dense floral organs. These flowers have been selected by horticulturists for increased number of petals. Researchers have found that the morphology of these flowers is because of strong mutations in the AGAMOUS homolog in these plants, which leads to them making a large number of petals and sepals.[99] Several studies

n diverse plants like petunia, tomato, Impatiens, maize etc. have suggested that the enormous diversity of flowers is a result of small changes in genes controlling their development.[100] Some of these changes also cause changes in expression patterns of the developmental genes, resulting in different phenotypes. The Floral Genome Project looked at the EST data from various tissues of many flowering plants. The researchers confirmed that the ABC Model of flower development is not conserved across all angiosperms. Sometimes expression domains change, as in the case of many monocots, and also in some basal angiosperms like Amborella. Different models of flower development like the The fading boundaries model, or the Overlapping-boundaries model which propose non-rigid domains of expression, may explain these architectures.[101] There is a possibility that from the basal to the modern angiosperms, the domains of floral architecture have gotten more and more fixed through evolution. Monocotyledons ( /?m?nk?tli?dn/[1]), also known as monocots, are one of two major groups of flowering plants (or angiosperms) that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon (seed-leaf), in contrast to the two cotyledons typical of dicots. Monocots have been recognized at various taxonomic ranks, and under various names (see below). The APG II system recognises a clade called "monocots" but does not assign it to a taxonomic rank.