Overview of green plants
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Overview of Green Plants. Chapter 30. Defining Plants. The kingdom Viridiplantae includes land plants and green algae Red and brown algae are excluded The green algae split into two major clades Chlorophytes Charophytes Streptophyta includes the Charophytes and all land plants

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Overview of Green Plants

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Overview of Green Plants

Chapter 30


Defining Plants

  • The kingdom Viridiplantae includes land plants and green algae

    • Red and brown algae are excluded

  • The green algae split into two major clades

    • Chlorophytes

    • Charophytes

  • Streptophyta includes the Charophytes and all land plants

  • All green plants arose from a single species of freshwater algae


Defining Plants


Defining Plants

  • Land plants have two major features

    • Protected embryos

    • Multicellular haploid and diploid phases


Defining Plants

Adaptations to terrestrial life

  • Evolution of leaves that increase photosynthetic surface area

  • Protection from desiccation by a waxy cuticle and stomata

  • Shift to a dominant vertical diploid generation


Plant Life Cycles

  • Humans have a diplontic life cycle

    • Only the diploid stage is multicellular

      Plants have a haplodiplontic life cycle

    • Multicellular diploid stage = Sporophyte

    • Multicellular haploid stage = Gametophyte

  • Plants have an alternation of generation

    • sporophyte → gametophyte → sporophyte → etc.


Plant Life Cycles

  • Sporophyte (2N) produces haploid spores (N) by meiosis

  • Spores (N) divide by mitosis producing the gametophyte (N)

  • Gametophyte (N) produces gametes (N) by mitosis

  • Gametes (N) fuse to form the diploid sporophyte (2N)


process

process

process

The General Plant Life Cycle


Plant Life Cycles

As more complex plants evolved:

  • Diploid stage (sporophyte) became the dominant portion of the life cycle

  • Gametophyte became more limited in size

  • Sporophyte became nutritionally independent


Chlorophytes

  • Chlorophytes, sister taxa of the Streptophytes, are a diverse group including:

  • Chlamydomonas

    • Unicellular chlorophyte with two flagella

    • Have eyespots to direct swimming

    • Reproduces asexually as well as sexually


Chlorophytes

  • Volvox

    • Colonial chlorophyte

  • Hollow sphere of a single layer of 500-60,000 cells

  • A few cells are specialized for reproduction


Chlorophytes

  • Ulva

    • Multicellular chlorophyte

    • True haplodiplontic life cycle

    • Gametophyte and sporophyte have identical appearance


MITOSIS

Ulva life cycle


Charophytes

  • Charophytes are green algae related to land plants

Land plants


Charophytes

  • Charales (300 species)

    • Macroscopic

    • Plant-like plasmodesmata

    • Sister clade to land plants

  • Choleocaetales (30 species)

    • Microscopic

    • Plant-like mitosis

    • Next closest plant relatives


Bryophytes

  • Bryophytes are the closest living descendants of the first land plants

    • Called nontracheophytes because they lack tracheids (specialized transport cells)

    • Simple, but highly adapted to diverse terrestrial environments

    • Non-photosynthetic sporophyte is nutritionally dependent on the gametophyte

    • 3 groups: liverworts, hornworts and mosses


Bryophytes

  • Liverworts (phylum Hepaticophyta)

    • Have flattened gametophytes with liver-like lobes

  • Form gametangia in umbrella-shaped structures

  • Also undergo asexual reproduction


Bryophytes

  • Hornworts (phylum Anthocerotophyta)

    • Sporophyte has stomata

  • Sporophyte is photosynthetic

  • Cells have a single large chloroplast


Bryophytes

  • Mosses (phylum Bryophyta)

    • Gametophytes consist of small, leaflike structures around a stemlike axis

    • Anchored to substrate by rhizoids

    • Multicellular gametangia form at the tips of gametophytes

      • Archegonia – Female gametangia

      • Antheridia – Male gametangia

    • Mosses withstand drought, but not air pollution


Moss Reproduction


Tracheophyte Plants

  • Cooksonia, the first vascular land plant, appeared about 420 MYA

  • Only a few centimeters tall

  • No roots or leaves

  • Homosporous (spores are the same size and type)


Tracheophyte Plants

  • Vascular tissues are of two types

    • Xylem – Conducts water and dissolved minerals upward from the roots

      • contains tracheids

    • Phloem – Conducts sucrose and hormones throughout the plant

  • These enable enhanced height and size in the tracheophytes

  • Tracheophytes are also characterized by the presence of a cuticle and stomata


Tracheophyte Plants

  • Vascular plants have gametophytes reduced in size and complexity relative to sporophytes

  • Seeds

    • Highly-resistant structures that protect the plant embryo

    • Occur only in heterosporous plants

  • Fruits in flowering plants add a layer of protection to seeds

    • Also attract animals that disperse seeds


Tracheophytes

  • Vascular plants(tracheophytes)include seven extant phyla grouped in three clades

    • Lycophytes (club mosses)

    • Pterophytes (ferns and their relatives)

    • Seed plants


Lycophytes

  • Club mosses are the earliest vascular plants

    • They lack seeds

  • Superficially resemble true mosses but they are not related

  • Homosporous or heterosporous


Pterophytes

  • The phylogenetic relationships among ferns and their relatives is still being sorted out


Pterophytes

  • Whisk ferns

    • Saprophyte consists of evenly forking green stems without leaves or roots

  • Some gametophytes develop elements of vascular tissue

  • Often symbionts with fungi


Pterophytes

  • Horsetails

    • All 15 living species are homosporous

    • Constitute a single genus, Equisetum

  • Consist of ribbed, jointed photosynthetic stems that arise from branching rhizomes

  • High silica content in stems made them useful as “scouring rushes”


Pterophytes

  • Ferns

    • The most abundant group of seedless vascular plants with about 11,000 species

  • The conspicuous sporophyte and much smaller gametophyte are both photosynthetic


Pterophytes

  • The fern life cycle differs from that of a moss

    • Much greater development, independence and dominance of the fern’s sporophyte

  • Fern morphology

    • Sporophytes have rhizomes

    • Fronds (leaves) develop at the tip of the rhizome as tightly rolled-up coils then uncoil and expand


Pterophytes

Uncoiled fronds are called “fiddleheads” and are a delicacy among northern First Nation peoples


Pterophytes


Pterophytes

  • Fern reproduction

    • Most fern are homosporous

    • Produce distinctive sporangia in clusters called sori on the back of the fronds

    • Diploid spore mother cells in sporangia produce haploid spores by meiosis

    • At maturity, the spores are catapulted by snapping action


Seed Plants

  • Seed plants first appeared 305-465 MYA

    • Evolved from spore-bearing plants known as progymnosperms

  • The seed represents an important advance

    • Protects the embryo

    • Easily dispersed

    • Introduces a dormant phase in the life cycle


Seed Plants

  • Seed plants produce 2 kinds of gametophytes

    • Male gametophytes

      • Pollen grains

      • Dispersed by wind or a pollinator

    • Female gametophytes

      • Develop within an ovule

      • Enclosed within diploid sporophyte tissue


Seed Plants

  • There are two types of seed plants

    • Gymnosperms are plants with “naked seeds”

      • Ovuleis exposed on a scale at pollination

      • All lack flowers and fruits of angiosperms

    • Angiosperms are flowering plants

      • Ovules are enclosed in diploid tissue at pollination

      • The carpel (modified leaf) covers seeds and develops into fruit


Gymnosperms

  • There are four living groups

    • Cycadophytes

    • Gnetophytes

    • Ginkgophytes

    • Coniferophytes


Gymnosperms

  • Cycads (phylum Cycadophyta)

    • Slow-growing gymnosperms of tropical and subtropical regions

  • Sporophytes resemble palm trees

  • Have largest sperm cells of all organisms!


Gymnosperms

  • Gnetophytes (phylum Gnetophyta)

    • Only gymnosperms with vessels in their xylem

  • Contain three (unusual) genera

    • Welwitschia

    • Gnetum

    • Ephedra

      • ephedrine can be extracted from species of this genus


Gymnosperms

  • Ginkgophytes (phylum Ginkgophyta)

    • Only one living species remains

      • Ginkgo biloba

  • Dioecious

    • Male and female reproductive structures form on different trees


Gymnosperms

  • Conifers (phylum Coniferophyta) are the largest gymnosperm phylum and include:

    • Pines, spruces, firs, cedars and others

    • Coastal redwood – Tallest tree

    • Bristlecone pine – Oldest living tree

  • Conifers are sources of important products

    • Timber, paper, resin and taxol (anti-cancer)


Gymnosperms

  • Pines

    • More than 100 species, all in the Northern hemisphere

    • Produce tough needlelike leaves in clusters

    • Leaves have:

      • Thick cuticle and recessed stomata

      • Canals into which cells secrete resin


Pine reproduction


Angiosperms

  • Angiosperm origins are a mystery

  • The oldest known angiosperm in the fossil record is Archaefructus

  • The closest living relative to the original angiosperm isAmborella


Angiosperms


Angiosperms

  • Flower morphology

    • Primordium develops into a bud at the end of a stalk called the pedicel

    • Pedicel expands at the tip to form a receptacle,to which other parts attach

    • Flower parts are organized in circles calledwhorls


Angiosperms

  • Flower morphology

    • Outermostwhorl = Sepals

    • Secondwhorl = Petals

    • Thirdwhorl = Stamens(androecium)

      • Each stamen has a pollen-bearing anther and a filament (stalk)

    • Innermost whorl = Gynoecium

      • Consists of one or more carpels that house the female gametophyte


Angiosperms

The ovary eventually develops into the plant’s fruit


Angiosperm Reproduction


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