At this point, another major division is reached – the evolution of the seed. The trimerophytes had also branched into progymnosperms. These were seedless vascular plants with megaphylls and xylem and phloem tissue for support and conduction. They evolved into seed plants. Seeds are advantageous because they have a multicellular developed embryo with root stem and leaves already formed, as opposed to a spore which contains one cell. A seed also has a food supply in the ovule and a resistant coat around it to prevent desiccation. It can live for long periods of time at reduced rates of metabolism. Progymnosperms branched early on into gymnosperms and angiosperms.

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Gymnosperms
Anthophytes (Angiosperms)

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