Non-vascular & Seedless Vascular Plants

• For much of Earth's history, the terrestrial surface was lifeless
• Cyanobacteria and protists likely existed on land 1.2 billion years ago
• Around 500 million years ago, small plants, fungi, and animals emerged on land
• Since colonizing land, plants have diversified into roughly 290,000 living species
• Land plants


  Plants with terrestrial ancestors, even though some are now aquatic
• Land plants do not include photosynthetic protists (algae)
• Plants supply oxygen and are the ultimate source of most food eaten by land animals
• Green algae called charophytes


  The closest relatives of land plants
• Characteristics shared by land plants and some algae

  • Rings of cellulose-synthesizing proteins
  • Structure of flagellated sperm
  • Formation of a phragmoplast
• Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants
• Land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes
• Sporopollenin


  A durable polymer that prevents exposed zygotes from drying out and is also found in plant spore walls
• The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, and nutrient-rich soil
• Land presented challenges: a scarcity of water and lack of structural support
• Land plants diversified as adaptations evolved that enabled them to thrive despite challenges
• Embryophytes

  Plants with embryos
• Five key traits that appear in nearly all land plants but are absent in the charophytes

  • Alternation of generations
  • Multicellular, dependent embryos
  • Walled spores produced in sporangia
  • Multicellular gametangia
  • Apical meristems
• Alternation of generations


  A reproductive cycle where plants alternate between two multicellular stages: a haploid gametophyte that produces gametes, and a diploid sporophyte that produces spores
• Multicellular, dependent embryos


  The diploid embryo is retained within the tissue of the female gametophyte, and nutrients are transferred from parent to embryo through placental transfer cells
• Walled spores produced in sporangia


  The sporophyte produces spores in organs called sporangia, and the spore walls contain sporopollenin which makes them resistant to harsh environments
• Multicellular gametangia


  Gametes are produced within organs called gametangia, with female gametangia (archegonia) producing eggs and male gametangia (antheridia) producing sperm
• Apical meristems


  Plants sustain continual growth in their apical meristems, where cells differentiate into various tissues
• Additional derived traits include a cuticle, stomata, and mycorrhizae
• Fossil evidence indicates that plants were on land at least 470 million years ago
• Fossilized spores and tissues have been extracted from 450-million-year-old rocks
• Fossils of larger structures, such as sporangium, date to 425 million years ago
• Ancestral species gave rise to a vast diversity of modern plants
• Informal groupings of land plants

  • Nonvascular plants (bryophytes)
  • Vascular plants
  • Seedless vascular plants
  • Seed plants
• Bryophytes are not a monophyletic group
• Seedless vascular plants can be divided into clades

  • Lycophytes (club mosses and their relatives)
  • Monilophytes (ferns, horsetails, whisk ferns)
• Origin of land plants

  • EEN
  • ALGA
• Origin of vascular plants

  • Liverworts
  • Mosses
  • Hornworts
  • Lycophytes
  • Monilophytes
  • Gymnosperms
  • Angiosperms
• Millions of years ago (mya)

  500<|>450<|>400<|>350<|>300<|>50<|>0
• Land plants


  • Can be informally grouped based on the presence or absence of vascular tissue
  • Most plants have vascular tissue; these constitute the vascular plants
  • Nonvascular plants are commonly called bryophytes
  • Bryophytes are not a monophyletic group
• Seedless vascular plants


  • Can be divided into clades: Lycophytes (club mosses and their relatives), Monilophytes (ferns and their relatives)
  • Do not form a clade
  • Organisms that are grouped based on shared key biological features, rather than shared ancestry, can be referred to as a grade
• Seed plants


  • Form a clade and can be divided into further clades: Gymnosperms, the "naked seed" plants, including the conifers; Angiosperms, the flowering plants
• Seed


  An embryo and nutrients surrounded by a protective coat
• Bryophytes


  • Represented today by three phyla of small herbaceous (nonwoody) plants: Liverworts, phylum Hepatophyta; Mosses, phylum Bryophyta; Hornworts, phylum Anthocerophyta
  • These groups are thought to represent the earliest lineages to diverge from the common ancestor of land plants
• Bryophyte gametophytes


  • In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes
  • Sporophytes are typically present only part of the time
• Bryophyte life cycle


  1. Spore germinates into a gametophyte composed of a protonema and gamete-producing gametophore

  2. Mature gametophytes produce flagellated sperm in antheridia and an egg in each archegonium

  3. Sperm swim through a film of water to reach and fertilize the egg

  4. Zygote develops into a young sporophyte

  5. Sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome