Seedless Vascular Plants: Study with Video Lessons, Practice Problems & Examples

Seedless vascular plants, such as ferns and lycophytes, exhibit a sporophyte-dominant life cycle and primarily reproduce through spores. They possess vascular tissue reinforced with lignin, allowing for greater structural support. Sperm requires water for fertilization, limiting their habitat. These plants played a crucial role in carbon fixation, contributing to global cooling and coal formation. Ferns produce clusters of sporangia called sori, where spores develop into gametophytes, which contain reproductive structures like antheridia and archegonia. Understanding these processes highlights the ecological significance of seedless vascular plants in Earth's history.

Seedless Vascular Plants

Hi. In this video, we're going to talk about seedless vascular plants. Now you might recall that seedless vascular plants have a sporophyte dominant life cycle, and their gametophytes are quite small, but they're not yet at the microscopic level, like those of seed plants. Now, they're mostly homospores. However, there are some heterospore species, and they still reproduce through spores, as opposed to pollen, which we'll see in the seed plants. Now, the sperm still requires water to reach the egg, just like the nonvascular plants we looked at. And this is again going to limit the types of environments in which these plants can survive. Now, the seedless vascular plants are obviously part of vascular plants, which are called tracheophytes. And these are just plants that possess vascular tissue that's reinforced with lignin. Now seedless vascular plants fall into the categories lycophytes, which are actually the only vascular plants to have those microfills we saw, which are the little leaves that only have the singular vascular tissue running through them. And they include organisms like clubmosses, spike mosses, and quillworts. And if you have no idea what those are, don't really worry about it. You know, you can look them up if you want, but it's not really a big deal that you don't know what these plants look like. Now the example we're going to use mainly is the fern. And ferns are part of, monelophytes. And these also include horsetails as well. Now, what's really cool about seedless vascular plants is in the course of evolution, they're actually responsible for the removal of a lot of CO₂ from the atmosphere. And this actually led to the formation of glaciers because removing all of that CO₂ resulted in a cooling of the atmosphere. I mean, think about global warming today. Right? We talk about CO₂ getting into the atmosphere, causing global warming. Right? It's one of those greenhouse gases. Well, removal of CO₂ has, the opposite effect. It's gonna cause a general cooling. And this led to the formation of glaciers. Also, fixing all of this carbon led to the formation of coal. And it's kind of ironic, I think, to think about how, today we burn coal and put that CO₂ back in the atmosphere, right, and cause global warming, whereas these plants removed CO₂ from the atmosphere, made that coal, and caused a global cooling. Just kind of funny thing to think about. Now, fern sporophylls, right? Remember those modified leaves that have the sporangia? They actually produce clusters of sporangia we call Sori. And that's the plural, sorus is the singular. And these are again clusters of sporangia on the undersides of leaves, you can see some here. So these are sori. And here we have the gametophyte. And the gametophyte actually contains the antheridium and the archegonium. We obviously can't really see it in this picture but the antheridium is going to be down here. And up here, we're going to have the archegonium. And these tendrils coming out, these are the oops, rhizoids. Right? Which are going to sort of function like roots. Now remember that these are vascular plants, so they do in fact have roots, but the gametophyte does not. Only the sporophyte has roots. These gametophytes just have these rhizoids, which is fine because, remember, they're not the dominant part of the life cycle, it's the sporophyte that is now. So, these gametophytes aren't going to be really hanging around too long, so to speak. And, as we said before, the sperm requires water to get to the egg. Right? So the sperm will swim to the archegonium and produce an embryo, for the, or an embryo that will turn into the new sporophyte. And we can see a little graphic of the fern's life cycle here. We have the sporophyte which is the fern we're used to seeing. Right? These are the leaves. Here, we have all the roots and on the underside of leaves, we're going to have the sporangium that are going to produce spores. Those spores are going to turn into the gametophyte, which is kind of a weird looking picture. You know, this is again, what the gametophyte looks like. And, from this gametophyte, this spore, you know, this right here is the sporophyte sprout that I've just circled, and that is going to grow out of our gametophyte and turn into this large sporophyte again. So that's all I have for seedless vascular plants. I'll see you guys next time.

Here’s what students ask on this topic:

What are seedless vascular plants and how do they reproduce?

Seedless vascular plants, such as ferns and lycophytes, are plants that possess vascular tissues (xylem and phloem) but do not produce seeds. Instead, they reproduce through spores. These plants have a sporophyte-dominant life cycle, meaning the sporophyte (diploid) stage is the most prominent. The gametophytes (haploid) are relatively small and produce gametes. Sperm from the antheridia (male structures) require water to swim to the archegonia (female structures) to fertilize the egg, forming a zygote that grows into a new sporophyte. This reliance on water limits their habitats to moist environments.

What role did seedless vascular plants play in historical carbon fixation and climate change?

Seedless vascular plants played a significant role in historical carbon fixation by removing large amounts of CO₂ from the atmosphere. This process contributed to global cooling and the formation of glaciers. The fixed carbon was stored in plant biomass, which eventually led to the formation of coal deposits. This is particularly interesting because the burning of coal today releases CO₂ back into the atmosphere, contributing to global warming. Thus, these plants were crucial in shaping past climate conditions and continue to impact current climate dynamics through the carbon cycle.

What are sori in ferns and what is their function?

Sori are clusters of sporangia found on the undersides of fern leaves (sporophylls). Each sporangium within a sorus produces spores through meiosis. When the spores are mature, they are released into the environment, where they can germinate and grow into gametophytes. These gametophytes will then produce gametes, continuing the reproductive cycle. Sori are essential for the reproductive success of ferns, enabling them to disperse spores over a wide area and colonize new habitats.

How do the gametophytes of seedless vascular plants differ from those of seed plants?

The gametophytes of seedless vascular plants, such as ferns and lycophytes, are relatively small but still visible to the naked eye. They contain reproductive structures like antheridia (male) and archegonia (female). In contrast, the gametophytes of seed plants are microscopic and develop within the tissues of the sporophyte. For example, in flowering plants, the male gametophyte is the pollen grain, and the female gametophyte is the embryo sac within the ovule. This difference highlights the evolutionary shift towards greater protection and reduced size of gametophytes in seed plants.

Why do seedless vascular plants require water for fertilization?

Seedless vascular plants require water for fertilization because their sperm are flagellated and need to swim to reach the egg in the archegonium. This mode of fertilization is similar to that of nonvascular plants like mosses. The dependence on water limits these plants to moist environments where water is readily available for the sperm to travel. This requirement is a significant factor in the distribution and habitat preferences of seedless vascular plants.