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7.7: Life Cycle of Seedless Vascular Plants

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    Have you ever noticed these little capsules on moss?

    These tiny capsules produce spores. This is one stage in the process of reproduction in the mosses. Remember mosses and other seedless plants do not have flowers, so their life cycle is quite different from other plants.

    Reproduction in Seedless Plants

    Seedless plants can reproduce asexually or sexually. Some seedless plants, like hornworts and liverworts, can reproduce asexually through fragmentation. When a small fragment of the plant is broken off, it can form a new plant.

    Reproduction in Nonvascular Seedless Plants

    Like all plants, nonvascular plants have an alternation of generations life cycle. That means they alternate between diploid cell stages (having two sets of chromosomes) and haploid cell stages (having one set of chromosomes) during their life cycle. Recall the haploid stage is called the gametophyte, and the diploid stage is called the sporophyte.

    In the life cycle of the nonvascular seedless plants, the gametophyte stage is the longest part of the cycle. The gametophyte is the green photosynthetic carpet that you would recognize as a moss.

    The life cycle of nonvascular seedless plants can be described as follows:

    1. The male gametophyte produces flagellated sperm that must swim to the egg formed by the female gametophyte. For this reason, sexual reproduction must happen in the presence of water. Therefore, nonvascular plants tend to live in moist environments. Though the life of a nonvascular seedless plant is a cycle, this can be considered the initial step in the life cycle.
    2. Following fertilization, the sporophyte forms. The sporophyte is connected to, and dependent on, the gametophyte.
    3. The sporophyte produces spores that will develop into gametophytes and start the cycle over again.

    Reproduction in Seedless Vascular Plants

    For the seedless vascular plants, the sporophyte stage is the longest part of the cycle, but the cycle is similar to nonvascular plants. For example, in ferns, the gametophyte is a tiny heart-shaped structure, while the leafy plant we recognize as a fern is the sporophyte.

    The fern's sporangia, where spores are produced, are often on the underside of the fronds (Figure below). Like nonvascular plants, ferns also have flagellated sperm that must swim to the egg. Unlike nonvascular plants, once fertilization takes place, the gametophyte will die, and the sporophyte will live independently.

    This fern is producing spores underneath its fronds
    Figure \(\PageIndex{1}\): This fern is producing spores underneath its fronds.
    In ferns, the sporophyte is dominant and produces spores that germinate into a heart-shaped gametophyte
    Figure \(\PageIndex{2}\): In ferns, the sporophyte is dominant and produces spores that germinate into a heart-shaped gametophyte.

    Summary

    • In nonvascular seedless plants, the gametophyte (haploid) stage is the longest part of the cycle.
    • In seedless vascular plants, the sporophyte (diploid) stage is the longest part of the cycle.

    Explore More

    Use the resource below to answer the questions that follow.

    1. Where can the sorus on ferns be found?
    2. What is found in the sorus?
    3. How is the mechanism that causes spores to be released similar to the mechanism that causes water to move up xylem? Explain your answer.
    4. What is meant by a bisexual gametophyte?
    5. What is the affect of the plant hormone antheridiogen? Why is this hormone crucial to ferns?

    Review

    1. How do some seedless plants reproduce asexually?
    2. What is alternation of generations?
    3. Why must nonvascular plants live in moist environments?
    4. Compare and contrast the fern gametophyte and sporophyte.