-plant bodies composed of tissues produced by an apical meristem. -spores with tough walls. -life history of alternation of generations

Transcription

1 Chapter 21-Seedless Plants Major modern plant groups All groups of land-adapted plants have a common set of characteristics: -plant bodies composed of tissues produced by an apical meristem -spores with tough walls -life history of alternation of generations -all plants produce their spores in multicellular enclosures called sporangia

2 Traits that characterize the 5 modern plant groups DNA, fossils, and other characteristics have been used to construct plant phylogenies. Plant phylogeny indicates: Land-adapted plants form a monophyletic group (plants originated from a common ancestor).

3 Charophycean algae (Charophyta) are the modern protists most closely related to plants. Bryophytes The First Land Plants Bryophyte is the name for a group of related organisms that included the ancestor of all other land plants. Based on the appearance of fossil bryophytes, the transition to land took place over 475 million years ago.

4 Bryophytes are rather simple organisms, but they are found in a wide variety of habitats and are highly diverse, with over 25,000 described species. Bryophytes are very important in many ecosystems: Bryophytes have a number of features that are similar to their charophyte ancestors, but they also possess several features that are clearly important for life on dry land. Bryophyte features shared with charophytes: similar pigmentation starch production in the plastid cell walls primarily of cellulose (no lignin) a photosynthetic gametophyte similarly structured sperm a need for free water for sexual reproduction Chara Mnium

5 Key innovations that first appeared in bryophytes. 1.Sporophyte evolution Zygote is retained on the gametophyte. The zygote divides by mitosis to produce a multicellular sporophyte s till attached to the gametophyte. The bryophytes are the first plants with embryos. In bryophytes, the embryos are immature sporophytes that are embedded in the tissue of the multicellular gametophyte. This arrangement of the sporophyte growing from within the gametophyte provides protection and nourishment for the sporophyte and allow for the production of many spores that can withstand desiccation. 2. Gametophyte evolution Large and elaborate gametophyte generation, similar to many charophytes and not found in other land plants. Multicellular structures surround the gametes. These structures are called gametangia.

6 Key innovations that first appeared in bryophytes. Structure of a liverwort (early bryophyte) 3. Stomata and cuticle Structure of an angiosperm leaf Stoma, with guard cells Stomata are structures that allow gas exchange but at the same time reduce water loss. The waxy cuticle also helps prevent water loss. Bryophytes comprise three distinct lineages of plants that do not have lignified vascular tissue. Hornworts Phylum Anthocerotophyta Liverworts Phylum Marchantiophyta Mosses Phylum Bryophyta Bryophytes comprise three distinct lineages of plants that do not have lignified vascular tissue.

7 Hornworts Phylum Anthocerotophyta Simple thalloid gametophyte. Form symbioses with cyanobacteria which enter the thallus through pores. Only land plants with this algal characteristic. Basic hornwort form. Note the simple sporophyte. Detail of the hornwort sporophyte. Hornworts are sometimes epiphytic but can be found free-living on clay banks. Liverworts Phylum Marchantiophyta Grow primarily in moist, shady areas. Two different types: Thalloid liverworts Resemble hornworts, but the thallus is held to the soil surface by single-celled rhizoids. Leafy liverworts Look more like a moss, with distinct leaves and stem.

8 Liverworts Phylum Marchantiophyta The thalloid genus Marchantia The thallus has minute pores that function much like stomata. Marchantia reproduces the gametophyte generation asexually through the production of small vegetative structures called gemmae, which are produced in gemmae cups. Marchantia also reproduces sexually. Male structures, called antheridiophores, resemble very small umbrellas.

9 Liverworts Phylum Marchantiophyta The thalloid genus Marchantia Marchantia also reproduces sexually. Female structures, called archegoniophores, resemble little palm trees. After fertilization, the sporophytes develop under the archegoniophores. Leafy liverworts Leafy liverworts are similar in appearance to mosses, but the leaves of liverworts have two or three distinct rows, instead of the spiral arrangement of leaves on most mosses. The resulting flattened appearance is rather distinctive. Porella

10 Leafy liverworts The archegonia appear at the tips of short leafy branches. Antheridia are produced in the axils of leaves. The leafy liverwort sporophyte is very simple. Mosses Division Bryophyta Dawsonia, found in Australia and New Zealand, to 60 cm tall. The common moss Polytrichum, hair-cap moss Sphagnum, the moss of bogs. botit.botany.wisc.edu/images/130/bryophytes/bryophyta/ Mnium, sometimes called carpet moss

11 Mosses. Vegetative Structure The first vegetative stage of the gametophyte is the protonema. This stage looks very much like a filamentous green alga. The stems of mosses have specialized tissues: They have an epidermal layer, often with a cuticle. The inner cells are called the cortex. A central strand of conductive tissue is present in some mosses. Central Strand Cell types present in some mosses include hydroids, which conduct water upward. Leptoids, which move sugar throughout the plant. These simple conductive tissues are the early evolutionary steps toward the complex vascular systems of other land plants.

12 Mosses. Vegetative Structure The leaves of mosses are not leaves in the true sense of the word. They do not have conductive tissues that are present in the leaves of vascular plants. Mosses Life Cycle The sporophyte grows to form an upright capsule and seta. Haploid spores are produced and released from the capsule. The spores germinate into haploid male and female gametophytes Flagellate sperm are released from the antheridium and travel to the archegonium where fertilization occurs. The moss that you most commonly see is a combination of the leafy gametophyte and the sporophyte that does not have leaves.

13 The capsule, the region of the sporophyte where the spores are produced, is often covered by the calyptra. The capsule may also have an operculum. These features differ greatly among the various families of mosses. The calyptra is a membraneous covering that is actually a remnant of the archegonial wall. Operculum covered by a calyptra. The operculum eventually pops off to become the opening for spore dispersal. Mosses- Peristome teeth The capsule opening of many mosses has a particular structure called perostome teeth. When the moss dries, the teeth outcurve, which pulls spores out and discharges them. Longitudinal section through a moss capsule showing all the features.

14 Study outline for Chapter 21-Bryophytes Name the five modern plant groups. What are the common set of characteristics that all groups of land-adapted plants share? Which algae are most closely related to land plants? When did the transition from water to land occur? Define bryophyte. How are bryophytes important in ecosystems? Name the features that bryophytes share with charophytes. Name the key innovations that appeared in bryophytes during the transition from water to land. Define sporophyte evolution. Define gametophyte evolution. Define archegonium. Define antheridium. What are the three distinct lineages of bryophytes that do not have lignified vascular tissue? What is the phylum for hornworts? What is the phylum for liverworts? What is the phylum for moss? What is the difference between a thalloid liverwort and a leafy liverwort? Define leptoid. Define hydroid. Label the structures in the liverwort Marchantia. gemmae (n) gemmae cups (n) antheridophore (n) antheridia (n) archegoniophore (n) archegonia (n) developing sporophyte (2n)

15 Study outline for Chapter 21-Bryophytes Define operculum. Define seta. Define protenema. Define peristomal teeth. Define calyptra. Define leptoid. Define hydroid. Label the terms from the moss life cycle. sporophyte gametophyte capsule seta protonema antheridium archegonium egg sperm zygote spores Bryophytes- Label the following: hornworts, thallose liverwort, leafy liverwort and moss. List 3 characteristics for each picture.