Skip to content
Quick Guides

Plant Biology - Seedless Vascular Plants

Preview 6 of 19 pages

See the first 6 pages exactly as they appear in the document.

  1. Page 1
    Read page 1 as text

    Study Guide Plant Biology – Seedless Vascular Plants 1. Phylum Lycophyta: Club Mosses and More 1.1 An Ancient Group of Plants Lycophytes are the oldest living seedless vascular plants on Earth. They belong to one of the two main evolutionary lines of vascular plants. These two lines split very early — probably during the Silurian Period , and definitely by the Devonian Period . Because of this early split, lycophytes have evolved independently from other vascular plants for about 400 million years . Over time, they changed dramatically. They began as small, semi - aquatic plants and later grew into giant tree - like forms that dominated forests during the Coal Age for nearly 40 million years. As continents shifted and climates became drier, lycophytes gradually lost dominance. By the late Carboniferous to early Permian , most of the large forms became extinct. Interestingly, lycophytes developed features similar to flowering plants, even though they are not closely related. This is called convergent evolution . Traits like leaves, wood, tree forms, and seed - like reproductive structures evolved independently in both groups. 1.2 Lycophytes Today Today, about 1,200 species of lycophytes are still alive. They are grouped into three families: • Lycopodiaceae • Selaginellaceae (only one genus: Selaginella , about 700 species) • Isoetaceae (only one genus: Isoetes , about 100 species) Modern lycophytes are much smaller than their ancient relatives. None grow taller than about one meter , even in tropical regions where they are most abundant. Many tropical species are epiphytes , meaning they grow high up in tree canopies. In temperate regions, lycophytes are usually small, creeping, evergreen plants . In the past, people collected them to make simple evergreen coverings for graves. Some Selaginella species are famous as “resurrection plants.” These plants live in very dry environments. During droughts, they shut down their metabolism and curl into tight, brown balls that

  2. Page 2
    Read page 2 as text

    Study Guide look dead. When water becomes available, they quickly uncurl, turn green, and begin photosynthesis again — storing enough energy to survive the next dry period. Lycophytes are also found in cold regions , including the Arctic, and often form a ground cover in northern and mountain conifer forests. 1.3 Key Structural Features Lycophytes can be identified by two main features: 1. Vascular tissue arrangement 2. Microphyll leaves , which are small leaves with only one vascular strand Their sporangia (structures that produce spores) are kidney - shaped , just like those of their ancient ancestors. These sporangia are carried on sporophylls , which are grouped together into cone - like structures called strobili . In Selaginella and Isoetes , a small scale - like structure called a ligule is present near the base of the leaf. This feature helps distinguish these groups from other lycophytes. 1.4 Life Cycle of Lycopods (Lycopodiaceae) Members of the Lycopodiaceae are homosporous , meaning they produce only one type of spore. Each spore grows into a bisexual gametophyte that produces both eggs and sperm. Some gametophytes grow underground and depend on a mycorrhizal fungus for nutrients. Others grow above ground. This gametophyte stage can last a very long time — up to 15 years in some species — before reproduction occurs. After fertilization, the embryo develops slowly into a sporophyte. The young sporophyte may stay attached to the gametophyte and rely on it for nutrition for an extended period. 1.5 Life Cycle of Selaginella Selaginella species are heterosporous , meaning they produce two different types of spores: • Megaspores , which develop into female gametophytes • Microspores , which develop into male gametophytes

  3. Page 3
    Read page 3 as text

    Study Guide The female gametophyte develops inside the megaspore . When the spore wall breaks, the archegonia (structures containing eggs) are exposed. The male gametophyte produces biflagellate sperm , which are also released when the spore wall breaks. These sperm swim to the archegonia to fertilize the egg. After fertilization, the embryo develops within the archegonium , which stays inside the megagametophyte. This setup is similar to flowering plants, but there is an important difference: No integuments form , and therefore no seed coat develops . This structure is considered an early step toward seed evolution , but it is not a true seed. 1.6 The Isoetes Group The third lycophyte group, Isoetes , is also heterosporous . Its sporangia are found on quill - like sporophylls that grow in a tight cluster around a short, swollen stem called a corm . A unique feature of Isoetes is the presence of a cambium within the corm. This cambium produces secondary tissues , a trait that is uncommon among seedless vascular plants. Summary Lycophytes are a fascinating group of plants with a long evolutionary history. Although most of their ancient tree - sized forms are extinct, modern lycophytes show important evolutionary traits — especially those related to vascular tissue, leaves, and reprod uction. Studying them helps us understand how complex land plants, including seed plants, evolved over time.

  4. Page 4
    Read page 4 as text

    Study Guide 2. Phylum Sphenophyta: Horsetails 2.1 A Once - Giant Group, Now Much Smaller Long ago, during the Carboniferous Period , horsetails were part of a large group of woody, tree - sized plants that filled ancient forests. Today, only one herbaceous (non - woody) genus , Equisetum , remains. This genus includes about 15 living species . Even though modern horsetails are much smaller, they closely resemble their ancient ancestors. Because of this, Equisetum may be the oldest living genus of vascular plants and one that has changed very little over time. 2.2 How to Recognize a Horsetail Horsetails are among the easiest plants to identify . They have several distinctive features: • Jointed, ribbed, hollow stems • Stems contain large amounts of silica , which makes them rough

  5. Page 5
    Read page 5 as text

    Study Guide o When two stems are rubbed together, they make a rasping sound • This rough texture led to the old common name “scouring rush,” because early settlers used them for cleaning pots At each node (joint) on the stem, there is a ring of small leaves fused into a sheath . In many species, each node also produces a whorl of branches , giving the plant its familiar “horsetail” appearance . The aboveground shoots grow from a widespread rhizome system below the soil. 2.3 Habitat and Growth Horsetails need moist environments , at least during part of the growing season. This is because their sperm must swim through a thin film of water to reach the eggs — just like in ferns and other fern allies. However, horsetails do not rely only on sexual reproduction. They often spread vegetatively through their rhizomes , allowing them to colonize areas quickly without forming spores. 2.4 Distribution and Ecological Role Equisetum grows almost worldwide , except in Australia, New Zealand, and Antarctica . Most species are found in the Northern Hemisphere , especially between 40° and 60° north latitude . Despite their long history, modern horsetails have little commercial value and play only a minor role in most ecosystems today. 2.5 Life Cycle: Similar to Ferns The life cycle of Equisetum is very similar to that of ferns , with differences mainly in structure rather than process. Spore Production • Sporangia are grouped together in cone - like structures called strobili • In some species, these strobili grow at the tips of normal green shoots • In other species, the plant produces a short - lived, non - green, unbranched shoot that exists only to make spores Inside the strobili, sporangia hang in clusters of five to ten from umbrella - shaped structures called sporangiophores .

  6. Page 6
    Read page 6 as text

    Study Guide 2.6 Spores and Elaters Each spore is surrounded by four thickened bands called elaters . These elaters are hygroscopic , meaning they respond to changes in moisture. • When the air is dry, the elaters twist and move • This motion helps the spores float and disperse more easily (These elaters are different from the elaters found in mosses.) 2.7 Gametophyte Stage and Fertilization Once a spore germinates, it forms a small, green, flat (thalloid) gametophyte . This gametophyte: • Anchors itself to moist, nutrient - rich surfaces using rhizoids • Produces multiflagellate sperm , which require water to swim The sperm swim to the archegonium , where one sperm fertilizes the single egg . The resulting zygote develops into an embryo inside the archegonium. At first, the young sporophyte stays attached to the gametophyte , receiving nourishment. Once its roots, stems, and shoots are developed enough, the sporophyte becomes independent , completing the life cycle. Key Takeaway Horsetails are living fossils — simple, tough plants with an ancient design. While they no longer dominate forests, their structure and life cycle give us valuable insight into the early evolution of vascular plants and how modern plant groups developed over time. 3. Phylum Psilotophyta: Whisk Ferns Let’s take a closer look at Psilotophyta , a small and unusual group of plants commonly called whisk ferns . Even though they look ancient, there’s more to their story than meets the eye.

13 more pages in the full document

Unlock it once and it stays in your library, ready to chat with or turn into flashcards.

Unlock the full document

More Biology study materials

See all

Study this document with CramX

Once it is in your library, every tool can work from it.