Objectives What separates land plants from aquatic algae Know the life cycle of mosses vs ferns Prepare slides for examination with microscope Examine already-prepared slides Drawings Table Hepatophyta Liverworts The bryophyte phyla Anthocerophyta Bryophyta Hornworts True Mosses No vascular system No true roots – only rhizoids Primitive breathing pores - evolution of stomata Ecology Must live in moist habitats Spore dispersal Evolution Bluegreen algae Green algae Chara bryophytes © Wim van Egmond, Microsopy-uk.org Red algae Diploid – 2N Haploid – 1N Mitosis – somatic cell replication 2N → 2N + 2N ― Plants – gamete formation 1N → 1N +1N Meiosis 2N → 1N + 1N +1N + 1N Gamete – 1N Zygote – Union of two gametes Isogamy vs anisogamy Isosporous (homosporous) vs heterosporous Reproduction Most of the plant’s life cycle – 1N Short phase – 2N Gametes Mitosis 1N Zygote Union of gametes 2N Spores Meiosis 1N Marchantia Life Cycle Liverworts Liverworts Gemma cups Mnium True moss Sphagnum True moss Marchantia Liverwort Vascular plants - Seedless The pteridophyte phyla: Lycophyta Pterophyta Ferns Club mosses Horsetails Whisk ferns Sellaginella Resurrection plant Tolweb.org Reproduction Most of the plant’s life cycle – 2N Short phase – 1N Gametes Mitosis 1N Zygote Union of gametes 2N Spores Meiosis 1N Sori (singular – sorus) Sporangia (sporangium) spores Lab 7: Non-vascular and Vascular Seedless Plants Feel free to work remotely with your classmates, but you MUST write out your OWN answers; plagiarism, copying, and cheating are acts of academic dishonesty and will not be tolerated and will result in a score of 0. Please write your answers in a different color, in bold, or a different font in order to make your worksheet easier to grade. Introduction Watch this introductory video and proceed to the questions that follow. The objectives of the introduction are: ● Introduce the different groups of nonvascular plants and seedless vascular plants ● Identify the characteristics that differentiate plants from other eukaryotic organisms ● Understand the basics of plant life cycles Nonvascular plants and seedless vascular plants Bryophyte basics Nonvascular plants are also called bryophytes, which is NOT a monophyletic group (Figure 1). Despite the dominance of vascular plants today, there are about 17,000 species of bryophytes. They include liverworts (phylum Hepatophyta), hornworts (phylum Anthocerophyta), and mosses (phylum Bryophyta). Figure 1B. Bryophyte phylogeny. Note that the relative location of hornwort + liverwort + mosses group (bryophyta), their green algae ancestor, and Tracheophyta renders bryophytes a paraphyletic group. Most bryophytes are small and all lack vascular tissues, leaves, seeds, and flowers. Instead of roots, they have hair-like rhizoids that anchor them to the ground and absorb water and minerals from the soil. Bryophytes live in moist habitats because they are not very efficient at absorbing water and their male gametophytes are flagellated and require water to disperse. The major difference between this group and other plants is their life cycle; in all three groups of nonvascular plants, the ecologically persistent, photosynthetic phase of the life cycle is the haploid, gametophyte generation rather than the diploid sporophyte. Bryophyte sporophytes are very short-lived, are attached to, and nutritionally dependent on their gametophytes (Figure 2). Sporophytes consist of sporangia (aka capsule) that produces haploid spores by meiosis, seta that conducts materials to sporangium, and a foot that absorbs nutrients from the gametophyte. Figure 2. Moss life cycle (left) and life cycle forms of mosses (right). You don’t need to know the specifics of bryophyte life cycles! The right side shows anatomy: you should know these structures and their functions. Diversity of Nonvascular Plants Liverworts are small nonvascular plants that have leaf-like, lobed, or ribbon-like photosynthetic tissues rather than leaves. Liverwort rhizoids are thin, they lack stems, and are generally less than 10 centimeters tall. They often grow in colonies that carpet the ground. Hornworts are small nonvascular plants that have thin rhizoids and no stems. Their sporophytes are long and pointed and rise several centimeters above the gametophytes of the plant. Mosses are larger nonvascular plants that have coarser, multicellular rhizoids. They also have tiny, photosynthetic structures similar to leaves that encircle a central stemlike structure. Mosses grow in dense clumps, which help them retain moisture. Evolution of Early Land Plants Nonvascular and seedless plants dominated the first million years that plants existed on planet Earth. Based on molecular and anatomical similarities, we know that green algae (specifically from the protist phylum Charophyta) are the closest relatives of plants. Charophytes inhabit shallow edges of lakes, ponds, rivers, and streams and are known to occasionally dry out. The descendants of these green algae that could withstand drying out invaded the land and gradually adapted to the various challenges and benefits of living in the gravity-dominated terrestrial environment. The variety of these early adaptations eventually gave rise to the astounding diversity of plants known today and from the fossil record (290,000 described species in Kingdom Plantae!). Within bryophytes, scientists believe that the first nonvascular plants to evolve were the liverworts (based on similarities in spore chemical composition and cell wall) and that mosses have the most recent common ancestor with vascular plants. Vascular Seedless Plants There are two groups of vascular plants that lack seeds: Lycophyta (club mosses, spikemosses, and quillworts) and Monilophyta (ferns, horsetails, and whisk ferns). Seedless vascular plants do NOT comprise a monophyletic lineage. Seedless vascular plants dominated and diversified during the warm, wet Carboniferous period, and were the first plants to grow tall. Unlike the bryophytes, lycophytes and monilophytes have a vascular system, true leaves (the photosynthetic organ of plants), roots (a sporophyte organ that absorbs water and nutrients from the soil and anchors the plant), sporophylls (modified leaves that bear sporangia and therefore function in plant reproduction), and a life cycle dominated by the sporophyte form. The vascular system of plants is composed of two tissues: xylem (tissue consisting of mostly dead cells that conduct water and minerals upward from roots to the rest of plant) and phloem (living cells arranged into tubes that move sugars and organic nutrients throughout the plant). Questions to answer 1. Below is an image of a moss under a microscope (left) and in the field (right). Identify the labeled parts (hint: Google Mnium and look through the images that are returned - that will help you identify the labeled parts): a. b. c. d. e. What is the ploidy of part C? f. What is the ploidy of part D? 2. Why are mosses only found in wet places? 3. Below are images of the antheridium and archegonium of a liverwort under a microscope. a. Which is the antheridium, panel A or panel B? b. Which is the archegonium, panel A or panel B? c. What is the purpose of these two structures? d. Are these structures haploid or diploid? 4. Examine the diagram below, which illustrates the life cycle of a moss. In the space below, describe in your own words the life cycle of a typical moss. 5. The dots on the underside of the leaves of a fern are called sori (top image). a. Identify the sorus and sporangia based on the images provided below i. AA: ii. BB: b. Explain the function of each structure c. Where would you find the spores on this organism? 6. Below is an image of a horsetail, which is a seedless vascular plant, stem in cross section (left), a close up of a single vascular bundle (middle), and an entire specimen (right). Identify the labeled parts and briefly explain their function: a. b. c. d. 7. Complete the table below: Kingdom Phylum Common name Vascular ? Yes/No Sporophyte dominant? Y/N Seeds? Y/N Heterosporous ? Y/N Charophyta Bryophyta Hepatophyta Anthocerophyta Pterophyta Lycophyta Critical thinking about nonvascular and seedless vascular plants 8. Using what you know about natural selection, form a hypothesis (explanation) that explains how the ancestors of modern plants were able to invade land. 9. From the perspective of early plants, list two benefits and two challenges associated with life on land. 10. Briefly explain why the evolution of land plants was (and is) so critical to life as we know it on planet Earth. 11. What is the functional significance of a vascular system? Put another way, what did the evolution of a vascular system allow plants to do? 
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