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angiorepro213-page9 - compacted on the floral shoot to 1...

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Flowering Plant Reproduction - 9 Flower Parts and Evolution Flower structure and number and fusion of flower parts relates to the evolutionary specialization of flowering plants. Several trends are evident from the "ancestral" flowering plants to the evolutionarily derived (advanced) forms. The number of flower parts generally decreases with evolutionary specialization. The Magnoliides, for example, have indefinite numbers of floral parts; those that are more "advanced" have fewer, definite, numbers of floral parts. Early angiosperms lacked a showy perianth; clear distinction between calyx and corolla is an advanced evolutionary feature. The kinds of floral parts (calyx, corolla, androecium and gynoecium) become reduced with evolutionary complexity. The spiral arrangement of floral parts common in ancestral forms becomes
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Unformatted text preview: compacted on the floral shoot to 1 – 4 whorls in more advanced flowering plants. • Fusion of parts, particularly of carpels, (to themselves and other floral parts) is characteristic of the advanced flowering plants. • Inferior ovaries are associated with evolutionary specialization. • Zygomorphic flower shape is associated with evolutionary specialization. • Monoecious and dioecious flowers are considered an evolutionary advancement. • Pollen with one aperture (monocolpate) is found in the earliest angiosperms. Triaperturate pollen is believed to be more advanced. (Angiosperm evolution and diversity will be discussed in more detail in the plant diversity unit.)...
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