Plant Diversity I Level 1 Biological Diversity Jim Provan Campbell: Chapter 29.

Plant Diversity IPlant Diversity I

Level 1 Biological DiversityLevel 1 Biological Diversity

Jim ProvanJim Provan

Campbell: Chapter 29Campbell: Chapter 29

Main groups of land plantsMain groups of land plants

Four main groups:Four main groups:BryophytesBryophytes (mosses, liverworts and hornworts) (mosses, liverworts and hornworts)

— Differ from algae due to adaptation to terrestrial lifeDiffer from algae due to adaptation to terrestrial life— Mainly reproductive differences e.g. developing embryo Mainly reproductive differences e.g. developing embryo

attached to mother plantattached to mother plant

PteridophytesPteridophytes (ferns, lycophytes, horsetails etc.) (ferns, lycophytes, horsetails etc.)— Vascular system not found in bryophytesVascular system not found in bryophytes— Some bryophytes have a rudimentary water-conducting Some bryophytes have a rudimentary water-conducting

systemsystem

GymnospermsGymnosperms (conifers etc.) (conifers etc.)— Seed plants: embryo, food supply and protective Seed plants: embryo, food supply and protective

coveringcovering

AngiospermsAngiosperms— Flowering plantsFlowering plants

Highlights of plant evolutionHighlights of plant evolution

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Ten phyla of extant plantsTen phyla of extant plants

Common nameCommon name Approximate numberof extant species

Approximate numberof extant species

Nonvascular plants (bryophytes)

Division BryophytaDivision HepatophytaDivision Anthocerophyta

Vascular plants

Seedless vascular plantsDivision LycophytaDivision Pterophyta

Seed plantsGymnosperms

Division ConiferophytaDivision CycadophytaDivision GingkophytaDivision Gnetophyta

AngiospermsDivision Anthophyta

Nonvascular plants (bryophytes)

Division BryophytaDivision HepatophytaDivision Anthocerophyta

Vascular plants

Seedless vascular plantsDivision LycophytaDivision Pterophyta

Seed plantsGymnosperms

Division ConiferophytaDivision CycadophytaDivision GingkophytaDivision Gnetophyta

AngiospermsDivision Anthophyta

MossesLiverwortsHornworts

LycophytesFerns

ConifersCycadsGingkoGnetae

Flowering plants

MossesLiverwortsHornworts

LycophytesFerns

ConifersCycadsGingkoGnetae

Flowering plants

12,0006,500100

1,00012,000

550100

170

250,000

12,0006,500100

1,00012,000

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170

250,000

Plants probably evolved from Plants probably evolved from green algae called charophytesgreen algae called charophytes

Evidence suggests plants Evidence suggests plants and and charophytescharophytes evolved evolved from a common ancestor:from a common ancestor:

Homologous chloroplasts: Homologous chloroplasts: accessory pigments, accessory pigments, stacked thylakoids, DNA stacked thylakoids, DNA evidenceevidenceBiochemical: cellulose and Biochemical: cellulose and peroxisomesperoxisomesCell division: dispersed Cell division: dispersed nuclear envelope, nuclear envelope, persistence of spindle etc.persistence of spindle etc.Sperm ultrastructureSperm ultrastructurePhylogeneticsPhylogenetics

Differences between plants and Differences between plants and charophycean algaecharophycean algae

Apical meristemsApical meristemsLight and COLight and CO22 found above ground found above groundWater and nutrients mainly found below groundWater and nutrients mainly found below ground

Multicellular, dependent embryosMulticellular, dependent embryosAlternation of generations:Alternation of generations:

Occurs in some algae but Occurs in some algae but notnot charophyceans (no charophyceans (no sporophyte generation): evolved independently in land sporophyte generation): evolved independently in land plantsplantsDiffers from standard haploid/diploid life cycles in that Differs from standard haploid/diploid life cycles in that both stages are represented by multicellular bodiesboth stages are represented by multicellular bodies

Walled spores produces in sporangiaWalled spores produces in sporangiaMulticellular gametangiaMulticellular gametangia

Alternation of generationsAlternation of generations

Alternation of generations Alternation of generations (continued)(continued)

Most plants reproduce sexually and most are also Most plants reproduce sexually and most are also capable of asexual reproduction: all plants have life capable of asexual reproduction: all plants have life cycles with an cycles with an alteration of generationsalteration of generations::

Haploid Haploid gametophytegametophyte generation produces and alternates generation produces and alternates with a diploid with a diploid sporophytesporophyte generation generation gametophyte gametophyteLife cycles are heteromorphic i.e. have different morphologyLife cycles are heteromorphic i.e. have different morphologySporophyte is larger and more noticeable, except in mossesSporophyte is larger and more noticeable, except in mosses

Comparison of life cycles among divisions is Comparison of life cycles among divisions is instructive:instructive:

Points to an important trend in plant evolution - reduction of Points to an important trend in plant evolution - reduction of gametophyte generation and dominance of diploid gametophyte generation and dominance of diploid sporophytesporophyteSome features are adaptations to terrestrial environment - Some features are adaptations to terrestrial environment - replacement of flagellated sperm by pollenreplacement of flagellated sperm by pollen

Alternation of generations in plants Alternation of generations in plants may have originated by delayed may have originated by delayed

meiosismeiosis

Evolved independently in various groups of algae:Evolved independently in various groups of algae:Does not occur among modern charophytes - occurrence Does not occur among modern charophytes - occurrence in plants had a separate origin from alternation of in plants had a separate origin from alternation of generations in algaegenerations in algaeAppearance in plants Appearance in plants analogousanalogous to occurrence in algae to occurrence in algae

ColeochateColeochate may hold clues to evolution: may hold clues to evolution:Parental thallus retains eggs - zygote also attached to Parental thallus retains eggs - zygote also attached to parentparentThallus cells grow around zygote which enlarges, Thallus cells grow around zygote which enlarges, undergoes meiosis and releases haploid swimming sporesundergoes meiosis and releases haploid swimming sporesHaploid spores develop into new individualsHaploid spores develop into new individuals

Only diploid stage is zygote - no multicellular Only diploid stage is zygote - no multicellular diploid stage. This would arise if meiosis was diploid stage. This would arise if meiosis was delayed until after mitotic division of zygotedelayed until after mitotic division of zygote

Alternation of generations in plants Alternation of generations in plants may have originated by delayed may have originated by delayed

meiosismeiosis

MeiosisMeiosisdelayeddelayed

Zygotic mitosisZygotic mitosisproduces multicellularproduces multicellular

sporophytesporophyte

Adaptations to shallow water Adaptations to shallow water preadapted plants for living on preadapted plants for living on

landland

Many modern charophytes live in shallow water, Many modern charophytes live in shallow water, as did their ancestorsas did their ancestors~440mya (Ordovician ~440mya (Ordovician Silurian), climatic Silurian), climatic changes caused fluctuations in water levelschanges caused fluctuations in water levelsNatural selection favoured plants tolerant to Natural selection favoured plants tolerant to periodic drying - preadaptation to terrestrial life:periodic drying - preadaptation to terrestrial life:

Waxy cuticlesWaxy cuticlesProtection of gametesProtection of gametesProtection of developing embryosProtection of developing embryos

Eventually, accumulated adaptations made it Eventually, accumulated adaptations made it possible for ancestral plants to live above water possible for ancestral plants to live above water lineline

BryophytesBryophytes

The embryophyte adaptation The embryophyte adaptation evolved in bryophytesevolved in bryophytes

The embryophyte condition was The embryophyte condition was a pivotal adaptation - :a pivotal adaptation - :

AntheridiumAntheridium (male gametangium) (male gametangium) produces flagellated sperm cellsproduces flagellated sperm cellsArchegoniumArchegonium (female (female gametangium) produces egg - gametangium) produces egg - fertilisation/embryo development fertilisation/embryo development occur within female organoccur within female organ

Bryophytes are not totally Bryophytes are not totally independent of aquatic habitat:independent of aquatic habitat:

Need water for sperm to swim inNeed water for sperm to swim inHave no vascular tissue - diffusionHave no vascular tissue - diffusion

The gametophyte is the dominant The gametophyte is the dominant generation in the life cycle of generation in the life cycle of

bryophytesbryophytes

Mosses (Division Bryophyta)Mosses (Division Bryophyta)

A tight pack of many moss A tight pack of many moss plants forms a spongy mat plants forms a spongy mat that can absorb waterthat can absorb water

Each plant grips the Each plant grips the substratum with substratum with rhizoidsrhizoids

Photosynthesis occurs in Photosynthesis occurs in the upper parts of plantsthe upper parts of plants

Cover about 3% of land Cover about 3% of land surface and contain vast surface and contain vast amounts of organic carbonamounts of organic carbon

Liverworts (Division Liverworts (Division Hepatophyta)Hepatophyta)

Less conspicuous than Less conspicuous than mossesmossesSometimes have bodies Sometimes have bodies divided into lobesdivided into lobesLive cycle similar to Live cycle similar to mosses: sporangia have mosses: sporangia have elaters to aid dispersalelaters to aid dispersalCan reproduce asexually Can reproduce asexually from gemmaefrom gemmaeMost diverse in tropical Most diverse in tropical forestsforests

Hornworts (Division Hornworts (Division Anthocerophyta)Anthocerophyta)

Resemble liverworts but Resemble liverworts but sporophytes are horn-sporophytes are horn-shaped and grow from shaped and grow from mat-like gametophytemat-like gametophyte

Photosynthetic cells Photosynthetic cells have a single, large have a single, large chloroplastchloroplast

Most closely related to Most closely related to vascular plantsvascular plants

Additional terrestrial adaptations Additional terrestrial adaptations in vascular plantsin vascular plants

Regional specialisation of the plant bodyRegional specialisation of the plant body: evolution : evolution of roots to absorb water and stems/leaves to make of roots to absorb water and stems/leaves to make foodfoodStructural supportStructural support: no buoyancy from water, so : no buoyancy from water, so lignin became embedded into cell wallslignin became embedded into cell wallsVascular systemVascular system::

XylemXylem: conducts water and minerals from roots. Composed : conducts water and minerals from roots. Composed of dead, tube-shaped cells and provides structural supportof dead, tube-shaped cells and provides structural supportPhloemPhloem: conducts food throughout the plant. Composed of : conducts food throughout the plant. Composed of living cells organised into tubules and distributes sugars etc.living cells organised into tubules and distributes sugars etc.

PollenPollen and and seedsseeds: to transport gametes: to transport gametesIncreased dominance of the diploid sporophyteIncreased dominance of the diploid sporophyte

PteridophytesPteridophytes

The sporophyte-dominant life The sporophyte-dominant life cyclecycle

Exemplified by ferns:Exemplified by ferns:Familiar leafy plant is the sporophyteFamiliar leafy plant is the sporophyte

Gametophytes are small and grow on or below the soil surfaceGametophytes are small and grow on or below the soil surface

Vascular plants display two distinct reproductive Vascular plants display two distinct reproductive strategies:strategies:

Sporophyte of Sporophyte of homosporoushomosporous plants (e.g. ferns) produces a plants (e.g. ferns) produces a single type of spore which develops into a bisexual single type of spore which develops into a bisexual gametophyte with both male and female sex organsgametophyte with both male and female sex organs

Sporophyte of Sporophyte of heterosporousheterosporous plants produces two types of plants produces two types of spore:spore:

— Megaspores develop into female gametophytes (Megaspores develop into female gametophytes (archegoniaarchegonia))— Microspores develop into male gametophytes (Microspores develop into male gametophytes (antheridiaantheridia))

A sporophyte-dominant life cycle A sporophyte-dominant life cycle evolved in seedless vascular evolved in seedless vascular

plantsplants

MITOSISMITOSIS

Lycophytes (Division Lycophyta)Lycophytes (Division Lycophyta)

Includes club mosses and Includes club mosses and ground pinesground pinesDominated land through Dominated land through the Carboniferous Period the Carboniferous Period (340-280mya)(340-280mya)Some species of Some species of Lycopodium Lycopodium are are epiphytesepiphytes::

Sporangia borne on Sporangia borne on sporophyllssporophyllsSpores develop into Spores develop into inconspicuous gametophytesinconspicuous gametophytes

Mostly homosporousMostly homosporous

Horsetails (Division Horsetails (Division Sphenophyta)Sphenophyta)

Survived through Survived through Devonian and at peak Devonian and at peak during Carboniferousduring Carboniferous

Only genus is Only genus is EquisetumEquisetum::

Lives in damp locations Lives in damp locations and has flagellated spermand has flagellated sperm

HomosporousHomosporous

Conspicuous sporophyte Conspicuous sporophyte generationgeneration

Has photosynthetic, free-Has photosynthetic, free-living gametophytesliving gametophytes

Ferns (Division Pterophyta)Ferns (Division Pterophyta)

Co-existed with lycopods Co-existed with lycopods and horsetails in and horsetails in Carboniferous forestsCarboniferous forestsLarger leaves with Larger leaves with branched system of veins branched system of veins - fronds are compound - fronds are compound leavesleavesHomosporous:Homosporous:

Specialised sporophyllsSpecialised sporophyllsGametophyte is small and Gametophyte is small and fragilefragileEmbryo develops within Embryo develops within archegoniumarchegonium