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

Overview of Green Plants

Chapter 30


Defining plants

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


Overview of green plants

Defining Plants


Defining plants1

Defining Plants

  • Land plants have two major features

    • Protected embryos

    • Multicellular haploid and diploid phases


Defining plants2

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

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 cycles1

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)


The general plant life cycle

process

process

process

The General Plant Life Cycle


Plant life cycles2

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

  • 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


Chlorophytes1

Chlorophytes

  • Volvox

    • Colonial chlorophyte

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

  • A few cells are specialized for reproduction


Chlorophytes2

Chlorophytes

  • Ulva

    • Multicellular chlorophyte

    • True haplodiplontic life cycle

    • Gametophyte and sporophyte have identical appearance


Overview of green plants

MITOSIS

Ulva life cycle


Charophytes

Charophytes

  • Charophytes are green algae related to land plants

Land plants


Charophytes1

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

  • 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


Bryophytes1

Bryophytes

  • Liverworts (phylum Hepaticophyta)

    • Have flattened gametophytes with liver-like lobes

  • Form gametangia in umbrella-shaped structures

  • Also undergo asexual reproduction


Bryophytes2

Bryophytes

  • Hornworts (phylum Anthocerotophyta)

    • Sporophyte has stomata

  • Sporophyte is photosynthetic

  • Cells have a single large chloroplast


Bryophytes3

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


Overview of green plants

Moss Reproduction


Tracheophyte plants

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 plants1

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 plants2

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

Tracheophytes

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

    • Lycophytes (club mosses)

    • Pterophytes (ferns and their relatives)

    • Seed plants


Lycophytes

Lycophytes

  • Club mosses are the earliest vascular plants

    • They lack seeds

  • Superficially resemble true mosses but they are not related

  • Homosporous or heterosporous


Pterophytes

Pterophytes

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


Pterophytes1

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


Pterophytes2

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”


Pterophytes3

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


Pterophytes4

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


Pterophytes5

Pterophytes

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


Pterophytes6

Pterophytes


Pterophytes7

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

  • 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 plants1

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 plants2

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

Gymnosperms

  • There are four living groups

    • Cycadophytes

    • Gnetophytes

    • Ginkgophytes

    • Coniferophytes


Gymnosperms1

Gymnosperms

  • Cycads (phylum Cycadophyta)

    • Slow-growing gymnosperms of tropical and subtropical regions

  • Sporophytes resemble palm trees

  • Have largest sperm cells of all organisms!


Gymnosperms2

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


Gymnosperms3

Gymnosperms

  • Ginkgophytes (phylum Ginkgophyta)

    • Only one living species remains

      • Ginkgo biloba

  • Dioecious

    • Male and female reproductive structures form on different trees


Gymnosperms4

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)


Gymnosperms5

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

Pine reproduction


Angiosperms

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


Angiosperms1

Angiosperms


Angiosperms2

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


Angiosperms3

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


Angiosperms4

Angiosperms

The ovary eventually develops into the plant’s fruit


Overview of green plants

Angiosperm Reproduction


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