Plantae groups

What are three examples of nonvascular plants?

∙ Glaucophytes = chlorophyll a only; chloroplast with peptidoglycan;  some with no cell wall, some with cellulose

∙ Red algae = chlorophyll a only; phycobilins,; complex life cycles, no  flagellates cells; cellulose cell walls

∙ Green plants = chlorophyll a & b, starch (includes all green algae  and land plants); cellulose cell walls

∙ Streptophytes = plasmodesmata, apical growth, phragmoplast,  sporopollenin (Charophytes and land plants)

∙ Embryophytes = oogamous, sportic meiosis (land plants) ∙ Vascular plants = vascular tissues

What is phylum hepatophyta?

∙ Seed plants = seeds and pollen grains

∙ Flowering plants = flowers, double fertilization to produce  endosperm

abundant at 811PhylogenyofPlants Angiosperms most abundant species at 257,000 and Gymnosperms least  Green algae

What is the basic morphology of leafy moss?

Don't forget about the age old question of What is the byzantine empire known for?

∙ Loose term for mostly aquatic protists with chlorophylls a and b ∙ Includes two groups: one NOT related to land plants (Chlorophytes) and one that INCLUDES land plants (Streptophytes)

∙ Very diverse

∙ Oogmaous, isogamous, anisogamous

∙ Motile and non-motile

∙ Three classes

o Ulvophyceae: generally form neither a phycoplast nor a  phragmoplast; nuclear envelope persists; spindle persists no cell  plate

 Marine parenchymatous green algae

 Sproic meiosis

a

ar

cell

ring

a

ystem nd

;

le

 isogamous

o Chlorophyceae: form a phycoplast during cell division; a system of microtubules parallel to plane of division; nuclear envelope  persists, spindle disappears

 Zygotic meiosis  We also discuss several other topics like What is the principle of radiation balance?

 Isogamy

 Flagellated zoospores can function as sexual propagules or  gametes

o Charophyceae: Advanced groups form a phragmoplast during  cell division; a system of microtubules outside the spindle and  perpendicular to the plane of division; nuclear envelope breaks  down; spindle persists; cell plate is formed. Includes Chara and Coleochaete. Shared by land plants

ndChlorophyceae 

∙ Volvox

o Colonial chlorphytes

o Connected haploid flagellated vegetative cells in a hollow  gelatinous matrix; moves in a rolling motion

o Asexual daughter colonies form from specialized gonidia;  

eventually move inside the parent colony

∙ Coleaochaete

o ParenchymatousDon't forget about the age old question of Bateson and punnett refer to what?

o Retained egg and zygote, which undergoes immediate meiosis  after release (zygotic meiosis)

o Specialized multicellular structures for holding gametes  (gametangia)

o Sporopollenin in zygote covering

∙ Chara

o Parenchymatous

o Zygotic meisosis

o Branding apical growth

o Nodes and internodes Don't forget about the age old question of Who has legal ownership of the information?

o Plasmodesmata

o Entire covering of egg

∙ Spirogyra

Data suggests that the earliest plants that diverged from charophytes were  like present-day bryophytes. Also, liverworts are sister to all remaining land

ata from present

ggests that the

iverge from 

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• DNA sequence data from present

at liverworts are

maining land

day plants also suggests that the earliest plants to diverge from  We also discuss several other topics like Who is immanuel kant?

hyte green algae

charophytes were like present­day

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orts

bryophytes

• molecular data support the hypothesis that liverworts are

ar plants es

sister to all remaining land

plants

plants.  

• Ch = charophyte green algae

• Lv = liverworts

• Ms = mosses

• Hw = hornworts

• VP = vascular plants

First Colonized Land Organisms

∙ Earliest plants date to the Ordovician, around 470 million years ago;  nonvascular

∙ Numerous microfossils (spores and sporangial fragments) from  Ordovician; identical to liverwort spores

Copyright ©2006 by the National Academy of Sciences

∙ First vascular plant macrofossils 425 mya ∙ Early terrestrial plants were tiny

∙ Traits of early land plants

o Alternation of generations life cycle (sporic meiosis)

o Oogamous

o Apical growth

o Motile sperm; requirement for liquid water for fertilization, a  hold-over from an aquatic lifestyle If you want to learn more check out The monetary base refers to what?

o Internal conductive tissue common but probably not in the  earliest land plants; hydroids and leptoids in some; try xylem and phloem in others

∙ Many characteristics were adaptations to terrestrial habitats o Multicellular jacket of cells surrounding gametangia and  sporangia

o (in protists, gametangia and sporangia are generally unicellular) o Zygote and embryonic sporophytes retained in maternal  gametophyte tissue

o Spores contained in sporopollenin, a resistant compound not  commonly found in the green algae (recently discovered in  zygotes of the charophyte Spirogyra)

o Internal vascular/conduvtive system

 Conductive tissue (hydroids and leptoids found in present day mosses)

 True xylem and phloem

∙ Nonvascular plants

o Three phyla (do not together form a monophyletic group)  Heptatophyta – liverworts

 Anthocerophyta – hornworts

 Bryophyta – mosses

o Predominant gametophytes stage and a nutritionally-dependent  sporophytes

o All parenchymatous (form tissues), but produce no true xylem  and phloem (mosses produce hydroids and leptoids)

o Some have cuticle and stomates

Phylum Heptatophyta – Liverworts

∙ Called liverworts because some look superficially like liver tissue ∙ Both leafy and thallose kinds

∙ Thallus (nonvascular plant body) dorsiventrally flattened; dorsal side  has pores and ventral side has rhizoids and scales

∙ Asexual reproduction by gemmae

Marchantia

MarchantiaGametophyteswith

SurfacePoresofMarchantia

Cups

MarchantiaMalegametophytesproduceantheridiaindiskson

Gemma  

Cups

Surface spore

antheridial headsonantheridiophoresandFemalesproduce

Marchantia male gametophytes produce antheridia in disks on antheridial  archegoniaontheunder-surfaceof stalkedarchegonial headson

heads on antheridiophores and females produce archegonia on the under surface of stalked archegonial heads on archegoniophores  

archegoniophores(-phore, GK. pole)

Male Female

Liverwort-Sporophytes

Sporangium before and after opening to release spores

verwor – poropye

Sporangiumbeforeandafteropeningtoreleasespores LifeCycleofaCommonLiverwortMarchantia

5

4

1

2

3

1-2. Fertilizationtakesplaceatthebaseofthearchegoniumafter splashdispersal of motile spermfrommaletofemalegametophyte

3.After fertilization, diploidzygotedevelopsintoasporophyteontheunder surfaceofthe archegonial head

4-5. Maturesporophyteproducesandreleasesspores

Phylum Bryophyta

∙ Gametophyte leafy

∙ Asexual reproduction by fragmentation

BasicMorphologyLeafyMoss

Basic Morphology of Leafy Moss

“Leaf”(microphyll)

TopView

CrossSection

Moss Gametophytes

∙ Male gametophytes produce antheridia at apices; motile sperm ∙ Female gametophytes produce archegonia at apices; fertilization  takes place at the base of the archegonia

∙ Asexual reproduction by fragmentation (some produce  gemmae)

Phylum Anthocerophyta (hornworts)

∙ Gametophytes superficially similar to thallose liverworts

• Gametophyte superficially similar to thallose liverworts • Sporophyte is photosynthetic but still dependent on gametophyte for water, minerals; stomates and cuticle on sporophyte

• cells contain large central chloroplasts with pyrenoids (like many

∙ Sporophyte is photosynthetic but still dependent on gametophyte for  water, minerals; stomates and cuticle on sporophyte

algae; in contrast, plants have numerous small chloroplasts with no ∙ Cells contain large central chloroplast with pyrenoids (like many algae;  

pyrenoids)

in contrast, plants have numerous small chloroplast with no pyrenoids) • Representative Anthoceros

∙ Representative Anthoceros

Hepatophyta         Anthocerophyta   Bryophyta

stomates no sporophyte sporophyte elaters yes yes no cond. tissue no no yes chloroplast plant algal plant protonema rarely no yes asexual gemmae frag. frag., gemmae

Vascular Plants

∙ All produce true vascular tissue (xylem and phloem)

∙ More complex structurally than nonvascular plants

∙ All extant groups have a life cycle dominated by the sporophyte ∙ All extant groups include some heterosporous species (all seed plants  are heterosporous)

∙ Gametophytes small but multicellular; some unisexual and some  bisexual; some photosynthetic and some not

∙ Basically two groups, Lycophytes and Eupyllophytes (Monilophytes and  seed plants)

∙ Anatomy and Development

o All land plants develop apically and produce the same primary  tissues

o Secondary tissues produced also produced by seed plants

∙ Lignin gives wood its strength, even plant cannot breakdown this  polymer

∙ All land plants exhibit apical growth; some also produce secondary lateral  growth

o Primary tissues develop from apical meristems and develop into  primary plant body (roots, stems, leaves)

o Secondary tissues develop later within primary growth and permit thickening of the root and stem

Process begins during embryo

development and continues throughout

the life of the plant

∙ Plant tissues made up of many cell types

o Xylem

 Water-conducting tissue made up of tracheids and vessel members

o Phloem

 Food-conducting cells made up of sieve tube cells and  companion cells

∙ Epidermis

o Outermost layer of cells of stems and leaves, jigsaw puzzle  pattern of epidermal cells

o Stomates

 Guard cells surrounded by subsidiary cells

 Function together to regulate gas exchange and water loss ∙ Other specialized cells

o Trichomes (above ground — stems and leaves)

o Root hairs (below ground – roots)

∙ Cortex and pith

o Ground tissues make up ground tissue system; tissues  recognizable by location

o Cortex peripheral

o Pith central

• cortex peripheral

• pith central

• primary tissues similar in all parts of primary growth

(leaf, stem, root)

• primary meristems also the same

∙ Primary tissues similar in all parts of primary growth (leaf, stem, root) ∙ Primary meristems also the same

• arrangement of tissues is different

∙ Arrangement of tissues is different

Shoot Anatomy

∙ Shoot: stem and leaves

∙ Primary tissues arise from apical meristem

∙ Lateral shoots arise externally from axillary buds

Leaves

∙ Part of the shoot stem

∙ Develop from shoot apex (as does stem)

Roots

∙ Generally underground plant organs that anchor plant in soil and  absorb water and inorganic nutrients

∙ Also develop apically through the same developmental pattern

Cortex in roots has an endodermis

∙ Innermost layer of root cortices is called the endodermis

∙ Endodermal cells in a single layer with a suberin-containing  Casparian strip

∙ This strip is attached to the plasma membrane of the cell and also the  Casparian strip of each adjacent cell

∙ Blocks movement of water between cells; water must move through a  cell membrane to enter the vascular cylinder in center

As the root matures, the endodermis becomes sealed with suberin and water no longer moves into the vascular cylinder

Stele types:

Arrangements of vascular tissues changed over time in land plants ∙ Protosteles

o Solid core of xylem in center

o Still observed in some seed plant roots

∙ Siphonosteles

o Solid cylinders of vascular tissue with pith in center  

SEED PLANTS characterized by

o Fern rhizomes (stems)

secondary growth

o Has c-shape xylem/phloem with leaf gap in center

∙ Eusteles

Secondary growth

o Pith in center

o Vascular bundles in circle

∙ Atactosteles

• takes place within primary growth

o Scattered vascular bundles

after primary tissues are formed

o In monocot stems

• develops from secondary

SEED PLANTS characterized by secondary growth

meristems and enables plant to

Secondary growth

grow in diameter

∙ Takes place within primary growth after primary tissues are formed ∙ Develops from secondary meristems and enables plant to grow in  • sequence of development:

diameter

∙ Sequence of development:

Vascular cambium

 xylem ose in m

e of

lar

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ular

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∙ Produces secondary xylem and phloem adjacent to primary xylem and  phloem; develops between primary xylem and phloem initially ∙ As growth in diameter continues, pressure on peripheral tissues causes them to slough off

∙ Cell types in secondary xylem and phloem same as those in primary  xylem and phloem

∙ Appearance different:

o Stacked appearance of cells

o Presence of vascular rays

 Cells of rays also produced by vascular cambium

 Oriented radially in growth

Cork cambium

∙ Initiates first in cortex as epidermis is disrupted

∙ Produces cork to the outside and phelloderm to the inside; the out  layers become heavily filled with suberin (all layers together called  periderm)

∙ Provides a waterproof protective layer as epidermis disappers

          r called periderm)

es a waterproof protective layer as epidermis  ears

• in an old woody 

stem, most tissues 

are secondary:

• wood

(secondary xylem)

• bark (secondary 

phloem and 

periderms toward

the outside in the

outer bark)

Earliest vascular plants fossils: Rhynie Chert, Scotland, 425 mya No leaf-like organs, photsynthetic stems only

Early Devonian Landscape – 400 Ma

∙ Small plants only – non-vascular and early vascular

The Carboniferous Landscape (ca. 360 Ma)

ylls are

 are found in ups

nching from a

ophytes

ascular 

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∙ Lycopods and Pteridophytes Dominate

o Some estimates make lycopods the source for 70% of Coal

VASCULAR PLANTS

Differentiation of sporophyte

∙ Stems above and below-ground (rhizomes); both vertical and  horizontal; earliest protosteles,; later siphonosteles

∙ Roots frequently adventitious from rhizomes

∙ Leaves either none (sometimes small nonvascular scales), small  (microphylls) and large (megaphylls)

∙ Reproductive leaves called sporophylls; bear sporangia o Sporophylls sometimes clustered together into strobili (cones) Microphylls and Megaphylls are produced differently and are found in  different phylogenetic groups

∙ Microphylls form by branching from a protostele

o No leaf gap

o Characteristic of lycophytes

∙ Megaphylls form from vascular bundles that leave behind a leaf gap o Siphonosteles and eusteles

o Usually complex branching systems

o Characteristics of all other vascular plants (euphyllophytes) o Atactosteles in monocot stems

ocot stems Reprouctive biology

Homomospory vs heterospory (sporophytes)

∙ Homosporous sporophytes produce on type of spore

∙ Heterosporous sporophytes produce two types of spores

o Microspores in microsporangia; germinate and develop into male  gametophytes that produce antheridia; small and numerous

o Megaspores in megasporangia; germinate and develop into  female gametophytes that produce archegonia; large and few

Endospory vs exospory (gametophytes)

∙ Endosporic gametophyte develops inside spore wall

o All species with endosporic gametophytes are heterosporous ∙ Exosporic gametophytes break out of spore wall and develop  independently

o All species with exosporic gametophytes are homosporous

Lycophytes

∙ Sporangia are borne adjacent to microphylls

∙ Sometimes condensed into cone-like strobili

∙ Have microphylls

Lycopodium

∙ Homosporous sporophytes with microphylls

∙ Spores produced in sporangia attached to sporophylls clustered  together in cones

Selaginella

∙ Heterosporous sporophytes with microphylls

∙ Micro- and megaspores produced in separate sporangia clustered  together loosely on stem

∙ Endosporic gametophytes

∙ Embryo develops inside female gametophyte inside megaspore wall

Euphyllophytes

∙ Have true leaves with netted leaf venation and leaf gaps o The ferns and fern allies (monilophytes)

o The seed palnts

Monilophytes (ferns and “fern allies)

∙ Sister group to seed plants

∙ Horsetails, whisk ferns, leptosporangiate ferns

∙ All shed spores into the environment

∙ Typically produce their spores in bead-shaped sporangia (GK. monilo string of beads)

Horsetails

∙ 1 genus/15 species

∙ world-wide distribution

∙ Equisetum

Whisk ferns

∙ Psilotum and Tmesipteris

∙ 2 genera/17 species

∙ world-wide, frost-free

Leptosporangiate ferns

∙ extant ~12,000 species

∙ Stem can be any of: rhizome, trunk, or vine

∙ Distribution of sporangia distinguish leptosporangiate fern  species

∙ Sporus (pl. sori) – aggregation of sporgangia

∙ Indusium – flap

FernLifeCycle

SwimmingSperm!

Seed plants

∙ Macrofosslis appear first in fossil record 365 mya in late Devonian;  proably polyphyletic

∙ Seeds and pollen grains

∙ Gymnosperms – naked seeds

∙ Angiosperms – covered seeds

∙ Dominant sporophyte; nutritionally-dependent gametophytes ∙ Heterosporous sporophyte (microspores and megaspores) and  unisexual gametophyes

∙ Innovations

o Air-transported microgametophye (pollen grain)

 No anheridia; sperm transported in pollen tube to egg

o Integumented megasporangium (ovule, which develops into a  seed)

 Megagametophyte develops archegonia and eggs

 After fertilization, megagametophyte provides nourishment to embryo

 No need for liquid water for fertilization

Seed

∙ An embryo surrounded by nutritive tissue and enveloped by a seed  coat; the sexual reproductive propagule of the seed plants

Progymnosperms

∙ Extinct

∙ Produced a true vascular cambium that develops both secondary  xylem and secondary phloem (bifacial vascular cambium characteristic of seed plants)

∙ Produced first discrete vascular bundles (eustele, a more derived stele  type)

∙ Reproduction like ferns (NO SEEDS):

o Most were homosporous, but some were heterosporous o Since all seed plants are heterosporous, these would have been  the most likely progymnosperm ancestors of seed plants

Archaeopteris

∙ Woody progymnosperms common from 370 to 340 mya ∙ Both homosporous and heterosporous species in the genus ∙ Also called Callixyoln (the wood)

Two distinct groups of gymnosperms diverged from the progymnosperms:  seed ferns (extinct) and all other gymnosperms (polyphyletic)

Medullosa

∙ Carboniferous seed fern

∙ ‘ferny’ leaves named Neuropteris or Alethopteris

∙ seeds

∙ pollen sacs

Living gymnosperm clades:

∙ Conifers – pines, spruces, hemlocks, sequoias, yews, cedars, etc. ∙ Cycads – cycads

∙ Ginkgo – Ginkgo biloba

∙ Gnetophytes – Gnetum, Ephedra, Welwitschia

Cycads

∙ Tropical and subtropical

∙ Slow-growing

∙ Large stiff compound leaves

∙ Dioecious sporophytes produce either male or female cones (both  simple)

∙ Fleshy stems – much parenchyma

∙ Ancient and diverse groups

∙ Cycads of today thicker and shorter; evolved in Tertiary ∙ May have originated from seed ferns (Medullosans)

∙ Flagellated sperm in pollen tube

Gnetophytes

∙ Ancient group; represented in late Triassic

∙ Compound cones on separate plants (some Ephedra spp are  monoecious)

∙ Three genera, all of which have flowering plant characteristics ∙ Vessels in xylem

∙ Insect pollination

∙ Double fertilization

∙ Some lack archegonia

∙ Gnetum – dioecious tree or vine in old world wet tropics; insect  pollination; no archegonia

∙ Ephedra – looks like Equisetm

o Dioecious and monoecious arid plants world-wide

o Vessels, double fertilization and flower-like cones

Ephedra intermedia

∙ ‘Ephredra’ contains ephedrine, used a drug for thousands of years, but  recently has been marketed as an appetite suppressant and athletic  performance and energy enhancer

∙ FDA found that ephedrine show only short-term weight loss  effectiveness

∙ Drug raises blood pressure, stressing the circulatory system and  leading to more serious health problems like cardiac arrest and  strokes

∙ The ban is in effect for dietary supplements like ephedra, ma huang, sida cordifolia, and pinellia

∙ Welwitschia - stem buried in desert soils

∙ Grows in Namib Desert in Africa

∙ Dioecious, cone-bearing; two strap-shaped leaves

∙ Forms vessel in xylem; egg tube grows towards pollen tube; no  

archegonia

∙ Ginkgoes

∙ Ginkgo biloba only living species

∙ Dioecious sporophytes; males produce pollen; female produce  

single seeds at end of short stalks; fleshy seed coat; flagellated  

sperm cells

∙ Known primarily for dietary supplement

∙ Conifers

∙ Pine life cycle

∙ Sporophyte with leaves, stems, and roots, all with primary and  

secondary vascular tissues

∙ Stems made up of long shoots and short shoots

∙ Reproductive structures (cones) are modified long and short shoots;  separated by sex

MALE FEMALE

Female (ovulate) cone

ot

• modified long shoot

• larger and more

complex than male cone

s with

ring

• cone axis is a modified stem with modified stems

inserted 

(ovuliferous scales) 

in early

inserted laterally in the

ngia, cells is to

axils of modified leaves (nonphotosynthetic bracts)

s (n)

∙ “female” or ovulate cones modified long shoots o modified long shoot

o larger and more complex than male cone

o cone axis is a modified stem with modified stems (ovuliferous  scales) inserted laterally in the axils of modified leaves  

(nonphtosynthetic bracts)

o ovule (integumented megasporangia) are produced in the  early spring on the upper surface of the scales

o a single cell (megaspore mother cell, 2n) inside the  

megasporangium (nucellus) inside the integuments of each  ovule undergoes meiosis to produce four megaspores (n),  three of which are smaller and eventually die

o the remaining functional megaspore begins to divide and form a female gametophyte inside the nucellus, which remains  

• at this time, pollen captured inside the female cone in the

inside integuments

previous spring germinate and pollen tubes grow toward eggs

o at maturity, the female gametophyte forms two archegonia  with eggs at the micropyle end of each ovule

• fertilization is therefore internal and requires no water

o at this time, pollen captured inside the female cone in the  previous spring germinate and pollen tubes grow toward eggs • zygote (2n) develops into an embryo with numerous 

 fertilization is therefore internal and requires no water

o zygote (2n) develops into an embryo with numerous  

embryonic leaves (cotyledons), root and stem

embryonic leaves (cotyledons), root and stem

∙ “male or staminate condes modified short shoots

o modified short shoot

o simple

o modified stem axis with modified leaves bearing  

microsporangia (microsporophylls) inserted laterally;  

produced in early spring

o within microsporangia microspore mother cells (2n) undergo  meiosis to produce miscrospores (n)

 microscpores undergo two mitotic divisions to produce a 4-celled macrogametophyte (pollen grain)

 pollen grain at maturity contains two prothallial cells

(vegetative), a tube cell and a generative cell

o Ultimately, some pollen grains land in a female cone where  

they germinate to form a pollen tube, a cytoplasmic extension

of the tube cell, which will carry the generative nucleus with it

• pine seed is made up of three parts, each with a distinct

genotype

o Later, the generative nucleus gives rise to daughters, one of  which divides to produce two sperm nuclei

∙ Pine seeds are made up of three parts, each with a distinct  

• seed coat (2n) develops from the remnants of the

genotype

integuments and nucellus of the parent sporophyte

o Seed coat (2n) develops from the remnants of the  • female gametophyte tissue (n) serves as a food supply for

integuments and nucellus of the parent sporophyte

the embryo

o Female gametophyte tissue (n) serves as a food supply for the embryo

• embryo (2n), the second­generation sporophyte

o Embryo (2n), the second-generation sporophytes

∙ Pollination and fertilization take place one year apart in pine, usually o Pollination is the transfer of pollen from the male cone to the  female (first spring)

o Fertilization is the fusion of gametes (second spring)

∙ Seeds are dispersed when mature; sometimes the end of the  second year, sometimes later

o Some species dispersed by animals or fire to open cones

o Life cycle of all gymnosperms similar to that of pine

∙ Unique characteristics of gymnosperm life cycle

o 1. Reduced gametophyte – dependent on sporophyte

o 2. No antheridia; pollen tube transports male gametes to site  of fertilization; no water required

o 3. Gametes not produced until after pollination

o 4. Seeds protected by seed coat and embryos

ANGIOSPERMS (flowering plants)

∙ a monophyletic group of derived gymnosperms that all share certain features (synapomorphies)

o Flowers

o Double fertilization that creates endosperm (nutritive tissue in seed)

o Seeds covered by mature flower tissues (fruits)

∙ Origins unclear

o Morphological data suggest an origin in the now-extinct seed  ferns

o Molecular data suggest an ancient origin in the Triassic (245  mya)

o Fossil angiosperm-like pollen in the Jurassic (160 mya)

o Oldest actual macrofossil angiosperms (Archaefructus) from  the Cretaceous (125 mya)

Archaefructus – ca. 127 Ma. possible example of earliest known angiosperm  showing pistils separated from pollen bearing organs and no petals or sepals

Angiosperm

phylogeny

Basal ­ 3% spp.

Monocots ­ 22% spp.

www.mobot.org/MOBOT/Research/APweb/

Angiosperm characteristics Flowers

Eudicots ­ 75% spp.

∙ Highly reduced gametophytes (7-celled female, 2-3 celled male) ∙ Two integuments around the ovule

 ∙    Double fertilization 

o Endosperm

 ∙    The carpel 

o Fruits

∙ Phloem with companion cells

∙ Vessel elements

∙ As compared to gymnosperms reproduction, angiosperm reproduction  is energetically less costly (“cheaper”), faster, promotes extensive  outcrossing, which may speed the evolution of new adaptations, as  

well as opportunities for genetic isolation among incipient species via  animal pollination. This is likely why they predominate today.

Four concentric whorls in a flower: sepals, petals, stamens, pistils

Flower Anatomy

Sepals: outermost whorl, sometimes green, sometime other colors, if fused,  collectively called a calyx

Petals: Next whorl inside sepals, colored if animal pollinated; if fused,  collectively called a corolla

Stamens: fused microsporangia (anthers) supported by a stalk (filament);  these may also be fused together or to petals

Pistil: central structure made up of one or more carpels (leaves bearing  ovules) rolled into tubes; at the tip is a sticky stigma connected by a long  style or a swollen base (ovary) containing ovules

Naked ovules on the edge of a leaf become enrolled and encapsulated in a hollow vessel. This matches what we see during flower development.

Microsporangia on leaves that gets smaller and more streamlined over time. Many stamens in basal angiosperms are “leaf­like” in appearance.

What does angiosperm phylogeny tell us about the evolution of the flower?

Amborella trichopoda- A rare new Caledonian Shrub, most primitive  angiosperm

∙ Dioecious, small, unisexual flowers with spiraled parts, and no vessels ∙ Sister to all other extant angiosperms

Variation in Flower structure

∙ Magnolia Flower

o Radially symmetrical

o Many individual tepals

o Carpels and stamens

o Evolved earlier

o Regular, complete, perfect

∙ Orchid Flower

o Bilaterally symmetrical

o Fusion of parts

o Evolved later

o Irregular, incomplete

∙ Regular flowers: have all members of a whorl are similar in shape and  size

∙ Irregular flowers: where one or more members of whorl differ from the  others in shape and/or size

∙ Complete Flowers: have all flower parts (sepals, petals, stamens, pistil) ∙ Incomplete flowers: are missing some parts

∙ Perfect flowers: have both stamens and pistils

∙ Imperfect flowers: are either staminate or pistillate

Plants

∙ Hermaphroditic plants have perfect flowers; most species are of this  sort

∙ Monoecious plants have imperfect flowers, but both staminate and  pistillate flowers are on the same plant; Begonia, corn, pine ∙ Dioecious plants have only staminate or pistillate flowers at an given  time; holly, willow, gingko

Angiosperm life cycle: gametophytes (pollen grains and embryo sacs)  develop in anthers and ovules

∙ Male gametophytes (pollen grains) develop inside anthers (fused  microsporangia)

o Tapetum cells nourish spores then degenerate

o Microspore mother cell (2n) undergoes meiosis to form four  microspores (n)

o When mature pollen is transported (by wind or animals) to the  top of the pistil (stigma), it germinates and a pollen tube carrying sperm nuclei grows towards the base of the pistil (ovary) where  ovules are maturing

∙ Female gametophyte

o Develops inside an ovule as in gymnosperms; however, ovules  are enclosed in the ovary

o Female gametophyte develops from a single functional  megaspore (n); three mitotic divisions form a mature female  gametophyte (embryo sac)

o Develops from the functional megaspore and undergoes  three mitotic divisions

o At maturity, it has seven cells and eight nuclei:

 Two polar nuclei that migrate from each end to the center  of a large central cell

 Three antipodal cells at the end of the micropyle end

 Two synergid cells bordering the eggs

 One egg cell

Pollination

∙ Mature pollen is transported (by wind or animals) to the top of the pistil (stigma)

∙ Mature pollen of correct species germinates and a pollen tube carry  sperm nuclei grows towards the base of the pistil (ovary) where ovules  are maturing. The generative cell divides to form 2 sperm cells (not  flagellated)

Double Fertilization

∙ The pollen tube makes contact with the embryo sac and deposits  sperm nuclei inside:

o One sperm nucleus fuses with the egg to form a zygote (2n) o The other sperm nucleus fuses with the polar nuclei to form an  endosperm nucleus (3n)

o This triploid nucleus develops into endosperm

o Double fertilization in angiosperms results in production  of endosperm

Angiosperm Seed is made up of three parts

1. Seed coat (2n) develops from the remnants of the integuments and  nucellus of the parent sporophyte

2. Endosperm tissue (3n) serves as a food supply for the embryo 3. Embryo (2n) is the daughter plant of the adult sporophyte

Endosperm (3n) is also produced during embryology

∙ As the embryo grows, food stored in endosperm is sometimes stored in cotyledons; for ex. In legume seeds (beans, peas, peanuts, etc), there  is frequently no endosperms at maturity; stored in cotyledons ∙ In other seeds, endosperm is abundant; for ex. In grains, coconuts, etc.

Monocot seeds

∙ Corn fruit (with fused seed)

∙ Pericarp actually fused seed coat and fruit wall

∙ Extensive endosperm

∙ Embryo with a single cotyledon (scutellum is interpreted as a modified  cotyledon)

Evolution of endosperm

∙ Double fertilization evolves first in gymnosperms (seen in Ephedra and  Gnetum); creates two embryos; female gametophyte nurtures embryo ∙ In basal angiosperms, double fertilization creates a diploid embryo and  a diploid endosperm—essentially two embryos, one of which nurtures  the other (no nurturing female gametophyte)

∙ In derived angiosperms, double fertilization creates a diploid embryo  and a triploid endosperm

How is double fertilization to produce endosperm adaptive? Theoretical work  has focused on two things:

1. Energetics: it costs less energy

a. Gymnosperms produce a relatively large and costly female  gametophyte early in the life cycle

b. Angiosperms produce a small 7-celled female gametophyte late  in the life cycle

2. Flexibility: Plants can make cost:benefit adjustments to current  resources

a. Gymnosperms are committed early (a year in advance) to  mature a certain number of ovules

b. Angiosperms can abort ovules they can’t afford to mature at little cost

Trends over time in land plant evolution:

1. Increase in size of vascular plants

a. Nonvascular plants were and still are small

b. Vascular plants became very large in the Carboniferous and the  largest plants groups thereafter have been vascular plants 2. Increased protection of reproductive tissues

a. All lands plants have tissues surrounding reproductive parts b. Seed plants have additional covers; angiosperms have the most  protection

3. Reduction of gametophyte size of vascular plants

a. Nonvascular plants have a dominant gametophyte

b. Early vascular plants probably had isomorphic gametophytes and sporophytes

c. Seedless vascular plants include heterosporous species with  endosporic gametophytes

d. Seed plants have further reduced gametophytes

e. Angiosperms have the most reduced gametophytes

Green algae (Chlorophyta, Ulvophyta, Charophyta}

Unique (derived):

∙ Chlorophyll b

∙ Phycoplast (Chlorophyta)

∙ Phragmoplat (Charophyta)

Holdover (shared):

∙ Cellulose (red algae and other clades)

∙ Alternation of generations (red algae and other clades)

∙ Oogamy (many other clades)

∙ Flagellated cells (many other clades)

Non-vascular plants (Hepatophyta, Anthocerophyta, Bryophyta): Unique (derived):

∙ Multicellular gametangia (archegonia and antheridia)

∙ Embryos develop in maternal tissue

Holdover (shared):

∙ Phragmoplast (Charophytes)

∙ Alternation of generations

∙ Oogamy

∙ Flagellated sperm

Seedless vascular plants (Monilophytes, Lycophytes)

Unique (derived):

∙ Heterospory (microspores and megaspores)

∙ Vascular tissue (xylem and phloem)

∙ True routes, stems and leaves

Shared with ancestors:

∙ Homosporys (and exosporic gametophyes)

∙ Archegonia and antheridia

Gymnosperms (Coniferophyta, Gnetophyta, Cycadophyta, Ginkgophyta) Unique (derived):

∙ Pollen grains (no antheridia)

∙ Internal fertilization

∙ Ovules (integumented megasporangia)

∙ Seeds (covered embryos with food)

Holdover (shared):

∙ Heterospory

∙ Vascular tissue and secondary growth (Progymnosperms) ∙ Archegonia

Angiosperms (Anthophyta):

Unique (derived):

∙ Endosperm

∙ Fruits

∙ Reduced gametophytes

∙ No archegonia

Holdover (shared):

∙ Vascular tissue (secondary growth, progymnosperms) ∙ Double fertilization (Ephedra and Gnetum)

∙ Heterosporous sporophytes, endosporic unisexual gametophytes ∙ Pollen grains and ovules