Description
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Plantae groups
∙ 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
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∙ 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
We also discuss several other topics like What is the principle of terrestrial climate?
∙ 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 We also discuss several other topics like Bateson and punnett refer to what?
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
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 Don't forget about the age old question of Why are information technology ethical issues important?
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; Don't forget about the age old question of Moral luck means what?
eventually move inside the parent colony
∙ Coleaochaete
o Parenchymatous
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 We also discuss several other topics like The money multiplier refers to what?
o Nodes and internodes
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
like presentday
ta support the
• DNA sequence data from present
at liverworts are
maining land
day plants also suggests that the earliest plants to diverge from
hyte green algae
charophytes were like presentday
rts
s
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
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
o
ular
in
∙ 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
d a leaf gap usteles
nching
other vascular s)
∙ 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