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Lecture #5. Plant Diversity I: Non-vascular plants & Seedless Vascular plants. 1.2 billion years ago (BYA) – appearance of cyanobacteria on land 500 million years ago (MYA) – appearance of plants, fungi and animals more than 290,000 known plant species today

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lecture 5
Lecture #5

Plant Diversity I:

Non-vascular plants

&

Seedless Vascular plants

slide2
1.2 billion years ago (BYA) – appearance of cyanobacteria on land
  • 500 million years ago (MYA) – appearance of plants, fungi and animals
  • more than 290,000 known plant species today
  • plants inhabit all but the harshest environments
    • such as some mountaintops, deserts areas and polar regions
  • many plants have returned to their aquatic “roots”
    • e.g. some species of sea grasses
  • most present-day plants are terrestrial
  • presence of plants has enabled other life forms to survive on land
    • through their production of O2
plants and algae
Plants and Algae

Archaeplastida

Unikonta

Fungi

Animalia

Plantae

Chlorophyta

Charophyta

Rhodophyta

(Opisthokonta)

(Viridiplantae)

  • evolution of plants proposed from algae
    • closest relatives are located with the clade Charaophycea
    • these share a common ancestor with the clade Chlorophyta – include the green algae
    • similarities with algae:
      • multicellular
      • photosynthetic autotrophs
      • cell walls with cellulose
      • chlorophylls a and b

Choanoflagellates

Charophyceans

Plants

Fungi

Metazoans

Red algae

Chlorophytes

Ancestral eukaryote

4 key traits of plants
4 key traits of plants
  • four key traits of plants (and charophyceans)
    • provided by not only morphologic evidence but genetic evidence
    • 1. rose-shaped complexes for cellulose synthesis – both charophyceans and land plants have rosette cellulose-synthesizing complexes
    • 2. peroxisome enzymes – peroxisomes have enzymes that help minimize the loss of organic production as a result of photorespiration

Rosettes

4 key traits of plants1
4 key traits of plants
  • four key traits of plants (and charophyceans)
    • 3. flagellated sperm structure – similar to the charophyceans
    • 4. formation of a phragmoplast= group of microtubules that forms between the daughter nuclei of the dividing plant cell during mitosis
adaptations by land plants
Adaptations by Land plants
  • advantages of a terrestrial life:
    • stronger exposure to sunlight for photosynthesis
    • atmosphere offered more CO2 for photosynthesis
    • soil rich in nutrients
    • initially relatively few herbivores
  • movement onto land would require protection of the zygote from drying out
    • development of layer of durable polymer called sporopellenin– prevents exposed zygote from dessication
  • movement onto land resulted in the development of specific adaptations– facilitated survival and reproduction on land
    • e.g. development of a structural system to withstand the forces of gravity
    • e.g. changes adapting to the relative scarcity of water
  • these adaptations have defined the plant kingdom
adaptations by land plants1
Adaptations by Land plants
  • what adaptations are unique to plants?
  • depends on how you draw the boundary separating plants from algae
  • some traits are related to terrestrial life
    • for the earliest land plants – mycorrhizal associations with fungi for nutrient absorption
    • epidermis with a waxy covering called a cuticle
    • production of secondary compounds that are products of secondary metabolic pathways
      • primary metabolic paths produce lipids, carbohydrates, amino acids – not unique to plants
    • secondary paths produce compounds such as:
      • tannins, terpenes and alkaloids (defense against herbivores and parasites)
      • phenolics (flavonoids – absorb UV radiation, deter attacks by pathogenic microbes)
slide8

Kingdom Plantae contains the plants called embryophytes – plants the develop from embryos

  • however, current debate advises some changes – 2 options:
    • Kingdom Streptophytae – Embryophytes (land plates) + Charophyceans

OR

    • Kingdom Viridiplantae – Embryophytes + Charophyceans + Chlorophytes

Viridiplantae

Streptophyta

Plantae

Charophyceans

Red algae

Embryophytes

Chlorophytes

Ancestral alga

hey guys how about confusing the issue
Hey guys! How about confusing the issue?
  • botanists do not use the term phyla when classifying the plant kingdom – use divisions
  • currently accepted organization: development of two lineages or divisions: non-vascular and vascular (390 MYA)
  • called the Bryophyta (non-vascular) and Tracheophyta (vascular)
  • ** plants can be divided into 2
  • major categories
  • non-vascular
  • vascular – subdivided into 2
  • more categories:
    • seedless
    • seed
kiss keep it simple stupid
KISS: Keep it simple stupid
  • ** plants can be divided into 2 major categories
  • non-vascular
  • vascular – subdivided into 2 more categories:
    • seedless
    • seed
land plants 4 characteristics
Land plants: 4 characteristics
  • 4 key derived traits found in plants:
    • 1. alternation of generations & multicellular, dependent embryos
    • 2. walled spores produced in sporangia
    • 3. multicellular gametangia
    • 4. apical meristems
land plants 4 characteristics1

Haploid multicellular

organism (gametophyte)

Mitosis

Mitosis

Gametes

Spores

MEIOSIS

FERTILIZATION

Zygote

Mitosis

Diploid multicellular

organism (sporophyte)

Land plants: 4 characteristics
  • 1. alternation of generations: alternation between multicellular haploid and diploid stages in a life cycle
    • seen also in some chlorophytans (algae) – but not in the charophyceans
    • these generations must be multicellular!!
    • haploid stage = gametophyte (haploid)
    • diploid stage = sporophyte (diploid)
    • the sporophyte is the mature plant produces haploid spores via meiosis
    • mitotic division of the haploid spore produces a multicellular gametophyte which is still haploid!!
land plants 4 characteristics2

Haploid multicellular

organism (gametophyte)

Mitosis

Mitosis

Gametes

Spores

MEIOSIS

FERTILIZATION

Zygote

Mitosis

Diploid multicellular

organism (sporophyte)

Land plants: 4 characteristics
  • 1. alternation of generations: alternation between multicellular haploid and diploid stages in a life cycle
    • the gametophyte is the reproductive part of the plant - produces haploid gametes by mitosis
    • gametes fuse via syngamy/fertilization to produce the zygote
    • zygote grows via mitosis to develop a new sporophyte
    • in non-vascular plants (ike ferns) – the sporophyte and gametophyte have distinct phenotypic appearances – but they are forms of the same species
    • in vascular plants – the gametophyte is microscopic
  • -sporophytes – multicellular, diploid, produce haploid spores via meiosis
  • -gametophytes – multicellular, haploid, produce haploid gametes via mitosis
slide14

1. Alternation of generations and multicellular dependent embryos cont….

    • in a life cycle with alternation of generations – the multicellular embryos develop from zygotes are retained within the female gametophyte
    • maternal tissue provides nutrients
    • plants with embryos are called embryophytes
    • embryo receives nutrition during development from placental transfer cells

Multicellular,

Dependent Embryos

Embryo

Maternal

tissue

10 µm

2 µm

Wall

ingrowths

Placental

transfer

cell (blue line)

land plants 4 characteristics3
Land plants: 4 characteristics
  • 2. walled spores in sporangia
    • within the diploid sporophyte are multicellular organs called sporangia (singular = sporangium) – production of haploid spores via meiosis
    • within a sporangium are diploid cells called sporocytes or spore mother cells – undergo meiosis to generate the haploid spores of the sporangium
    • the spores are protected bysporoporellin– key adaptation to terrestrial life

Walled Spores

Produced in Sporangia

Longitudinal section of

Sphagnum sporangium (LM)

Spores

Sporangium

Sporophyte

Gametophyte

Sporophyte and sporangium

of Sphagnum (a moss)

land plants 4 characteristics4
Land plants: 4 characteristics
  • 3. multicellular gametogangia
    • the haploid gametophyte undergoes production of haploid gametes within multicellular gametogania(singular = gametoganium)
    • the production of gametes is through mitotic division
    • female gametogania = archegonium- produces a single egg
    • male gametogania = antheridium– produces many flagellated sperm

Multicellular female

Gametangia

Archegonium

with egg

Female gametophyte

Multicellular

Male Gametangia

Antheridium

with sperm

Male gametophyte

Archegonia and antheridia

of Marchantia (a liverwort)

land plants characteristics

Apical

Meristem

of shoot

Developing

leaves

Land plants: characteristics
  • 4. apical meristems
    • light and CO2 are available above ground, water and minerals are found mainly in the soil
    • must be a way of collecting these components
    • plants do this by growing in length – through the production of stems and roots
    • these grow from stem cell-like tissues in the plant called meristems

Shoot

Root

land plants characteristics1

Apical

Meristem

of shoot

Developing

leaves

Land plants: characteristics
  • 4. apical meristems
    • apical meristem – localized regions of cell division located at the tips of shoots and roots
    • e.g. shoot apical meristem – cells divide by mitosis and cytokinesis to produce progenitor cells for the rest of the stem
    • e.g. root apical meristem
    • progenitor cells from the meristem are the source for the tissues of the stem and root

Shoot

Root

plant diversification
Plant Diversification
  • plant fossils dating back to 475 MYA
  • one major way to distinguish groups of plants is to classify them as: vascular & non-vascular
    • vascular tissue – extensive system formed by cells joined into tubes
    • conduct water and nutrients
    • those without these tubes – non-vascular plants
  • bryophytes: term used to refer to all non-vascular plants
    • do not form a monophyletic group or a single clade
    • known popularly as the mosses, liverworts and hornworts
    • is a debate as to how they are related to each other
    • don’t possess the advanced adaptations of vascular plants (e.g. roots & leaves)
    • they do share many characteristic with vascular plants – see the slide on 4 plant characteristics
  • vascular plants: clade that includes 93% of all surviving plant species
    • categorized into smaller clades:
      • 1. lycophytes – club mosses
      • 2. pteryophytes – ferns
      • 3. gymnosperms
      • 4. angiosperms
slide20

Land plants

Vascular plants

Bryophytes

Seedless vascular plants

Seed plants

Gymno-

sperms

Angio-

sperms

Hornworts

Mosses

Liverworts

Lycophytes

Pterophytes

Charophyceans

Origin of seed plants

(about 360 mya)

Origin of vascular plants

(about 420 mya)

Origin of land plants

(about 475 mya)

Ancestral

green alga

non vascular plants
Non-vascular plants
  • commonly known as the bryophytes
    • even though Bryophyta is one of the 3 phyla in this group
  • three phyla:
    • 1. Phylum Hepatophyta: liverworts
      • gametophytes are flattened into a thalloid or a leafy shape
      • e.g. Marchantia
    • 2. Phylum Anthocerophyta – hornworts
      • sporophyte can grow quite tall – sporangium along the length
    • 3. Phylum Bryophyta – mosses

Plagiochiladeltoidea= liverwort

Marchantiapolymorpha= liverwort

non vascular plants1
Non-vascular plants
  • mosses are not to be confused with the vascular mosses = lycophytes
  • moss life cycle is dominated by the gametophyte stage
    • gamete forming stage
    • anchored to the ground by rhizoids – long tubular single cells
    • NOT roots – not composed of tissues (cells only), lack specialized conducting cells and are not responsible for water and mineral absorption
  • some mosses are NOT mosses at all – Irish moss (red seaweed), reindeer moss (lichen), club mosses (seedless vascular plant)
bryophyte general life cycle the gametophyte
Bryophyte General Life Cycle: The Gametophyte
  • dominant stage in all bryophytes
  • when a bryophyte spore land on favorable habitats – it germinates and grows into a haploid gametophyte
  • first the spore develops into a threadlike protonema – covers a large surface area for absorption or water and minerals
  • each protonema produces a bud with an apical meristem (stem-cell like tissue for growth)
    • the AM generates gamete-producing structures known as gametophores
    • the tips of the gametophore bear the male or female gametangia
    • the protonema + gametophore = gametophyte

the gametophyte of mosses

is the actual moss!!

general life cycle the gametophyte
General Life Cycle: The Gametophyte
  • located in the gametophyte are the reproductive structures = gametangia
  • (singular = gametangium)
    • multiple gametangia develop on each gametophore
    • some bryophyte gametangiaare bisexual – both antheridium and archegoniumon the same gametophyte = monoecious
    • most mosses have separate antheridiumand archegoniumlocated on separate gametophytes on separate plants - dioecious
  • production of the gametes by mitosis since the gametophyte is haploid already!!!

antheridium

archegonium

general life cycle the gametophyte1

Gametophore of

female gametophyte

500 µm

Foot

Seta

Sporangium

Marchantia polymorpha,

a “thalloid” liverwort

Marchantia sporophyte (LM)

General Life Cycle: The Gametophyte
  • the gametophores of a liverwort are found at the end of stalks
  • they grow out of the gametophyte
  • the undersurface of these gametophores is where you find the antheridia and archegonia
  • since both of these are found on the same sporophyte plant = monoecious

the gametophyte of

the liverwort

is the actual liverwort!!

general life cycle the sporophyte
General Life Cycle: The Sporophyte
  • the sporophyte is very small in the non-vascular plant
  • fertilization is followed by development of the embryo within the archegonium
  • the embryo develops into a small sporophyte (diploid) - remains attached to the archegonium via a foot – for absorption of nutrients
  • the sporophyte is comprised of:
    • 1. seta (stalk)
    • 2. sporangium surrounded by a capsule
  • haploid spores develop in this sporangium via meiosis

moss

liverwort

sporophyte

general life cycle the sporophyte1
General Life Cycle: The Sporophyte
  • haploid spores develop in the sporangium via meiosis
  • the spores are dispersed and settle onto a new substrate
  • from these spores comes new protonemata(singular = protonema)
  • hornwort and moss sporophytes tend to be large and more complicated
  • liverwort sporophytes are microscopic
life cycle of a moss

Raindrop

Key

Male

gametophyte

Haploid (n)

Life Cycle of a Moss

Diploid (2n)

Sperm

“Bud”

Spores develop into

threadlike protonemata.

A sperm swims through a film of moisture to an archegonium and fertilizes the egg.

Antheridia

The haploid protonemata produce “buds” that grow into gametophytes.

Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.

Protonemata

“Bud”

Egg

Gametophore

Spores

Female

gametophyte

Archegonia

Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.

Rhizoid

Peristome

The sporophyte grows a long stalk, or seta, that emerges from the archegonium.

FERTILIZATION

Sporangium

(within archegonium)

MEIOSIS

Seta

Calyptra

Zygote

Capsule

(sporangium)

Mature

sporophytes

Foot

Embryo

Archegonium

The diploid zygote develops into a sporophyte embryo within the archegonium.

http://www.sumanasinc.com/webcontent/animations/content/moss.html

Young

sporophyte

Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.

Female

gametophytes

Capsule with

peristome (SEM)

the economics of moss
The Economics of Moss
  • mosses have very lightweight spores
  • easy distribution has allowed for the establishment of mosses around the globe
  • very common and diverse in moist forests and wetlands
  • can help retain nitrogen in the soil
    • many species harbor cyanobacteria that increase the availability of nitrogen to the moss
  • many species can survive drought and rehydrate when moisture reappears
the economics of moss1
The Economics of Moss
  • one wetland moss = Sphagnum or “peat moss”
    • peat moss = partially decayed remnants of Sphagnum
    • major component of partially decayed organic material called peat
    • regions with thick layers of peat = peatlands (3% of Earth’s surface)
      • peat contains 30% of world’s soil carbon
      • 450 billion tons of carbon is stored as peat
    • Sphagnum does not decay easily – phenolic compounds in its cell walls
    • peat – fuel source in northern Europe rather than wood
    • overharvesting of Sphagnum – could alter CO2 levels globally

Sphagnum moss

seedless vascular plants
Seedless Vascular Plants
  • bryophytes prominent during the first 100 million years of plant evolution
    • but they are not very tall
    • rarely over 20 cm in height
  • those plants that could achieve heights would have better access to sunlight, better spore dispersal
  • height would mean the need for a transport system for water and nutrients
  • would also need a structural support system
  • ferns are example of the evolution of plants that began to develop height and a vascular system
  • fossils of present day vascular plants date back 425 MYA
seedless vascular plants1
Seedless Vascular Plants
  • 4 major characteristics of vascular plants:
    • 1. dominant phase in the alternation of generations life cycle is the sporophyte
      • the opposite case with bryophytes
      • e.g. ferns – the leafy plant is the sporophyte
      • the sporophyte becomes the larger and more complex stage of the life cycle
      • dramatic reduction in gametophyte stage – may be under the soil
      • sporophyte no longer dependent on the gametophyte for nutrition
seedless vascular plants2
Seedless Vascular Plants
  • 4 major characteristics of vascular plants:
    • 2. development of vascular tissues – xylem and phloem
      • xylem – conduction of water and minerals
        • new cell population = tracheids
        • so vascular plants are often referred to as tracheophytes
        • water conducting cells contain a phenolic polymer – lignin
      • phloem – conduction of sugars and other nutrients
        • living cells
        • arranged into tubes for the distribution of sugars, amino acids and other organic products
seedless vascular plants3
Seedless Vascular Plants
  • 4 major characteristics:
    • 3. development of sporophylls: modified leaves that bear sporangia
      • vary in structure
      • two types: microphyll and megaphyll
      • e.g. in ferns – megaphylls with clusters of sporangia called sori
      • e.g. in lycophytes and gymnosperms – microphylls that form cone-like strobili
    • most seedless vascular plants are homosporous– one type of sporangium that produces one type of spore
      • this spore produces a bisexual gametophyte  egg and sperm
    • heterosporousspecies has two types of sporangia that develop into two types of spores
      • megasporangium - megaspore  egg
      • microsporangium - microspore sperm
seedless vascular plants4
Seedless Vascular Plants
  • 4 major characteristics of vascular plants:
    • 4. development of roots and leaves
      • rather than rhizoids – the sporophytes of vascular plants have evolved roots
      • roots– organs for the anchorage of the plant & absorption of water and nutrients
      • leaves– organs for the increase of vascular surface area to capture more solar energy
        • megaphylls are larger and have a highly branched vascular system (of veins) running through them
          • greater photosynthetic capacity
        • microphyllsare spine-like
          • supplied by a single, unbranched vein
          • appeared to have evolved first
evolution of leaves
Evolution of Leaves
  • evolution of microphylls from clusters of sporangia
  • evolution of megaphylls from an accumulation of branches on a stem
    • one branch with overtopping growth
    • smaller branches flattened and fused to one another and to the overtop branch
seedless vascular plants5
Seedless Vascular plants
  • two clades:
    • Phylum Lycophytaand Phylum Pterophyta
      • both have modified leaves called sporophyllsthat bear sporangia
      • two types of sporophylls: microphylls and megaphylls
      • most seedless vascular plants are homosporous
seedless vascular plants6
Seedless Vascular plants
  • Phylum Pterophyta – ferns, horsetails and whisk ferns
    • the pterophytes are divided by some botanists into separate phyla:
      • phylum Sphenophyta – horsetails
      • phylum Psilophyta – whisk ferns and relatives
      • phylum Pterophyta – ferns

Equisetum – horsetail fern

Psilotum – whisk fern

seedless vascular plants7
Seedless Vascular plants
  • Phylum Lycophyta – club mosses, spike mosses and quillworts

Quillwort

Isoetes

Club moss

Selaginella

phylum lycophyta

Strobili

(clusters of

sporangia)

Diphasiastrum tristachyum, a club moss

Phylum Lycophyta
  • club mosses, spike mosses and quillworts
  • 1200 species today
  • NOT true mosses since they have vascular tissue
  • most ancient line of vascular plants
  • modern lycophytes grow on tropical trees as epiphytes – BUT they are NOT parasites

epiphytic ferns

phylum lycophyta1
Phylum Lycophyta
  • microphyllline of evolution
    • distinct line of evolution that came out of the first land plants
    • development of leaves from clusters of sporangia
    • earliest lycophytes formed primitive leaves = enations
    • enations are now called microphylls
    • evolution of true roots – increased the size of the sporophyte
    • sporangia became clustered into compact cones or strobili
    • many species evolved heterospory
phylum pterophyta
Phylum Pterophyta
  • megaphyllline of evolution
    • development of leaves from a branching system of stems
    • seen in all seed vascular plants, ferns and arthrophytes (horsetails)
    • telometheory: main stem with dichotomously branching lateral stems
    • the lateral branches developed subdivisions – all on one plant
    • the last lateral branches = telomes
    • during evolution - tissue grew in between (webbing)
    • the telomes also acquired spore-forming ability
    • positioning of the branches became very regular and controlled

telomes

phylum pterophyta1
Phylum Pterophyta

alternate

  • development of phyllotaxy– arrangement of leaves on a stem
    • four basic patterns developed:
      • spiral phyllotaxy: lateral branches became arranged in a spiral pattern
      • alternating: stepwise arrangement of leaves
      • opposite: leaves directly opposite one another
      • whorled pattern: more complicated arrangement

opposite

whorled

phylum pterophyta2
Phylum Pterophyta
  • ferns
    • leaves are known as megaphylls
    • fern sporophyte is comprised of underground, horizontal stems called rhizomes
    • from these come vertical shoots that give rise to large leaves called fronds divided into pinna (or leaflets)
    • frond grows as the fiddlehead
      • leaf primordial cells as they grow curl inward
    • mature frond is called the megaphyll
    • megaphyll is a compound leaf with a center rachis and multiple pinna
    • the pinna itself may be may up of small pinnules
    • although some fern species – e.g. staghorn fern – have a simple leaf structure
phylum pterophyta3
Phylum Pterophyta
  • gametophyte is very small and shrivels and dies after the young sporophyte develops
  • the diploid sporophyte bears sporangia (singular = sporangium) clustered under the pinna in structures called sori (singular = sorus)
  • so one sorus is made up of multiple sporangia
    • a sporangium contains spore mother cells (2n)
  • the spore mother cells undergo meiosis to produce spores (n)  haploid gametophyte
the annulus and spore dispersal from the sporangium
The Annulus and spore dispersal from the Sporangium
  • http://www.youtube.com/watch?v=-xF83pHEx6Q
  • the individual sporangium is a stalked structure
  • at the end are spring-like devices that disperse the spores = annulus
      • annulus, a row of cells that bisects the sporangium like a sturdy spine.
      • annulus walls are permeable to water
      • as the sporangium dries, evaporating water is drawn out from the annulus, causing the cells to shrink – this pries the sporangium open
      • the presence of water within the sporangium propels the spores out like a catapult
fern life cycle

Key

Haploid (n)

Diploid (2n)

Antheridium

Spore

Young

gametophyte

MEIOSIS

Sporangium

Sperm

Archegonium

Egg

New

sporophyte

Mature

sporophyte

Sporangium

Zygote

FERTILIZATION

Sorus

Gametophyte

Fiddlehead

  • in the sporophyte – presence of multiple sporangia clustered into a sorus (sori = plural)
  • spores released from thesori and germination into a bisexual gametophyte
  • bisexual gametophyte develops male and female gametogania
    • male antheridium – for sperm production
    • female archegonium - for egg development
    • sperm are released and swim to the egg within the archegonium – fertilization and development into a diploid zygote
Fern Life Cycle

http://www.youtube.com/watch?v=9c9Zi3WFVRc

fern life cycle1

Key

Haploid (n)

Diploid (2n)

Antheridium

Spore

Young

gametophyte

MEIOSIS

Sporangium

Sperm

Archegonium

Egg

New

sporophyte

Mature

sporophyte

Sporangium

Zygote

FERTILIZATION

Sorus

Gametophyte

Fiddlehead

    • the zygote develops into a new diploid sporophyte – emerges from the gametophyte
  • growth of the sporophyte produces fronds or megaphylls
    • young, developing frond is called the fiddlehead
  • gametophyte disappears
  • fronds develop sporangia for the production of spores (via meiosis)
  • almost all fern species are homosporous
    • produce one kind of spore  bisexual gametophyte
Fern Life Cycle
  • heterosporousfern species have megasporangiumand microsporangium on the sporophyte – production of distinct spores for male and female gametophytes