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• 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• 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

(Opisthokonta) (Viridiplantae)

Rho

doph

yta

Pla

nts

Chl

orop

hyte

s

Cha

roph

ycea

ns

Red

alg

ae

Met

azoa

ns

Fung

i

Cho

anof

lage

llate

s

Archaeplastida

Ani

mal

ia

Chl

orop

hyta

Fung

i

Pla

ntae

Cha

roph

yta

Unikonta

Ancestral eukaryote

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 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• 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 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)

Viridiplantae

Streptophyta

Plantae

Red algae Chlorophytes Charophyceans Embryophytes

Ancestral alga

• 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

• 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)

Hey guys! How about confusing the issue?

** plants can be divided into 2major categories1. non-vascular2. vascular – subdivided into 2 more categories:

a. seedlessb. seed

KISS: Keep it simple stupid

** plants can be divided into 2 major categories1. non-vascular2. vascular – subdivided into 2 more categories:

a. seedlessb. seed

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

Mitosis

Spores

Mitosis

Mitosis

Zygote

Gametes

Haploid multicellularorganism (gametophyte)

Diploid multicellularorganism (sporophyte)

MEIOSIS FERTILIZATION

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!!

Mitosis

Spores

Mitosis

Mitosis

Zygote

Gametes

Haploid multicellularorganism (gametophyte)

Diploid multicellularorganism (sporophyte)

MEIOSIS FERTILIZATION

-sporophytes – multicellular, diploid, produce haploid spores via meiosis-gametophytes – multicellular, haploid, produce haploid gametes via mitosis

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 (like ferns) – the sporophyte and gametophyte have

distinct phenotypic appearances – but they are forms of the same species• in vascular plants – the gametophyte is microscopic

• 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

Maternaltissue

Embryo

2 µm 10 µm

Wallingrowths

Placentaltransfercell (blue line)

Land plants: 4 characteristics

Walled SporesProduced in SporangiaLongitudinal section ofSphagnum sporangium (LM)

Spores

Sporangium

SporophyteGametophyte

Sporophyte and sporangiumof Sphagnum (a moss)

– 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 by sporopellinin – key adaptation to terrestrial life

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 femaleGametangia

Archegonia and antheridiaof Marchantia (a liverwort)

Male gametophyte Antheridiumwith sperm

Female gametophyte

Archegoniumwith egg

Multicellular Male Gametangia

ApicalMeristemof shoot

Developingleaves

Shoot Root

– 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

Land plants: characteristics

ApicalMeristemof shoot

Developingleaves

Shoot Root

– 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

Land plants: characteristics

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

Ancestralgreen alga

Origin of land plants(about 475 mya)

Origin of vascular plants(about 420 mya)

Origin of seed plants(about 360 mya)

Land plants

Vascular plants

Seed plantsSeedless vascular plantsBryophytes

Live

rwor

ts

Hor

nwor

ts

Mos

ses

Lyco

phyt

es

Pter

ophy

tes

Gym

no-

sper

ms

Ang

io-

sper

ms

Cha

roph

ycea

ns

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

Marchantia polymorpha = liverwort

Plagiochila deltoidea = liverwort

Non-vascular plants

• two plant forms in the bryophyte life cycle– 1. Gametophyte– 2. Sporophyte

• sporophyte – bears spore-producing structures called sporangia (singular = sporangium)

• gametophyte – bears gamete-producing structures called gametangia (singular = gametangium)

• two kinds of gametangia– 1. Archegonium (female) – makes an egg– 2. Antheridium (male) – makes sperm

• moss life cycle is dominated by the gametophyte stage

Malegametophyte

“Bud” Spores develop intothreadlike protonemata.

Protonemata“Bud”

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

Raindrop

Sperm

Antheridia

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

Egg

Haploid (n)Diploid (2n)

Key

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

Archegonia

Rhizoid

Femalegametophyte

GametophoreSpores

Sporangium

Peristome

MEIOSIS

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.

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

FERTILIZATION(within archegonium)

Archegonium

Zygote

Embryo

Calyptra

Youngsporophyte

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

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

Capsule(sporangium)

Seta

Foot

Maturesporophytes

Capsule withperistome (SEM)

Femalegametophytes

Life Cycle of a Moss

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

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 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 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 Plants• 4 major characteristics:

– 3. development of sporophylls: modified leaves that bear sporangia• 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– heterosporous species has two types of sporangia that develop into two types of spores

• megasporangium - megaspore female gametophyte (egg)

• microsporangium - microspore male gametophyte (sperm) sperm

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

– microphylls are spine-like» supplied by a single, unbranched vein» appeared to have evolved first

Seedless Vascular plants• two divisions: Division Lycophyta and Division Pterophyta• ferns, horsetails and whisk ferns• the Pterophytes used to be divided by botanists into separate phyla:

• Phylum Sphenophyta – horsetails• Phylum Psilophyta – whisk ferns and relatives• Phylum Pterophyta – ferns

Equisetum – horsetail fern Psilotum – whisk fern

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

Diphasiastrum tristachyum, a club moss

Strobili(clusters ofsporangia)

epiphytic ferns

Phylum Lycophyta• microphyll line 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 (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

• megaphyll line of evolution – development of leaves from a branching system of stems– seen in all seed vascular plants, ferns and arthrophytes (horsetails)– telome theory: 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 acquired spore-forming ability

telomes

Spore

Sperm

Antheridium

Egg

Haploid (n)Diploid (2n)

Key

Younggametophyte

Sorus

Sporangium

MEIOSIS

FERTILIZATION

Archegonium

ZygoteNewsporophyte

Maturesporophyte

Sporangium

Gametophyte

Fiddlehead

Fern Life Cycle

• in the sporophyte – presence of multiple sporangia clustered into a sorus (sori = plural)

• spores released from the sori 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

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

Spore

Sperm

Antheridium

Egg

Haploid (n)Diploid (2n)

Key

Younggametophyte

Sorus

Sporangium

MEIOSIS

FERTILIZATION

Archegonium

ZygoteNewsporophyte

Maturesporophyte

Sporangium

Gametophyte

Fiddlehead

Fern Life Cycle

• 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

• heterosporous fern species have megasporangium and microsporangium on the sporophyte – production of distinct spores for male and female gametophytes