SeedPlants213 - Seed-Dispersing Plants - 1 The seed plants...

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Seed-Dispersing Plants - 1 The seed plants include the most successful plants in our earth's ecosystems today: the conifers and flowering plants, along with three other, less prominent, phyla. As we have discussed, the production of a seed, kept within an ovule for dispersal, gives a plant a distinct survival advantage over a single-celled spore, with the seed's nutrient-packed head start for the next generation and a variety of methods of dispersing to new locations. In addition, transporting sperm within a pollen grain frees the plant from the need for water for fertilization. Megaphylls, multi-stranded vascular leaves, provide more conduction and support for a larger surface area for photosynthesis. The ferns are the only spore- dispersing vascular plants that have functional megaphylls. As with all vascular plants, the dominant generation for the seed plants is the sporophyte generation. All seed plants are heterosporous. Heterospory often ensures greater genetic variation for sexual reproduction, providing for enhanced survival in changing or different environments. Both male and female gametophytes are dependent upon the sporophyte and female gametophytes are retained by the sporophyte plant until the seeds (of the next sporophyte generation) are mature. Seed Plant Traits Seed plant fossils date back about 350 million years.
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Seed-Dispersing Plants - 2 Phyla of Seed-dispersing Vascular Plants Fossil Groups Progymnospermophyta Pteridospermales – Fossil Seed Ferns Cordaitales – Primitive Conifer-like Bennettitales – Fossil Cycadeoides Extant Phyla Gymnosperms – Seed not protected by a fruit Four Phyla Cycadophyta: Cycads Coniferophyta: Conifers (e.g., Pine, Spruce, Fir, Hemlock, Yew) Ginkgophyta: Ginkgo Gnetophyta: Gnetum, Ephedra, Welwitschia
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Seed-Dispersing Plants - 3 Gymnosperm Phyla with Living Representatives Angiosperms (Flowering plants) – Seed protected by a fruit (the ovary) One Phylum Anthophyta – Flowering Plants Two Classes comprise 97% of Angiosperms Eudicotyledones (Eudicots) Monocotyledones (Monocots) Additional Groups comprise 3% of the more primitive Angiosperms Magnoliidae, including several orders Nymphaeales – Water Lilies Illiciales – Star Anise, Avocado and Pepper families Amborellales Archaefructales – Fossil progenitor of Magnoliides
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Seed-Dispersing Plants - 4 General Life History of the Seed-Dispersing Vascular Plants All seed plants are heterosporous. Male and female sporangia may be on separate plants (dioecious) or on the same plant (monoecious). Generally, sporangia are clustered in strobili. In Angiosperms, the flowering plants, the male and female sporangia may be in the same flower (bisexual), on different flowers on the same plant (monoecious), or on separate plants (dioecious). As learned previously, special terms are used for sporangia and gametophyte structures in flowering plants.
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SeedPlants213 - Seed-Dispersing Plants - 1 The seed plants...

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