EVOLUTION AND PLANT DIVERSITY
Chapter 29
Evolution of Green Algae

Plants share many characteristics
with many protists
 Multicellular,
eukaryotic,
and photoautotrophs
 Cell walls of cellulose
 Chloroplasts with chlorophylls a
and b

Charophytes are only algae that
share 4 distinctive traits with
land plants
 Identified
lineage as closest
relatives to land plants
Charophytes Traits

Rosette-shaped cellulose-synthesizing complexes


Peroxisome enzymes


Similar structure in land plants with and charophyceans
Formation of a phragmoplast


Help minimize loss of organic products from photorespiration
Flagellated sperm structure


Proteins in the PM that synthesize cellulose in cell wall
Microtubules that form between daughter nuclei to create
new cell wall in dividing cells
Doesn’t imply land plants are descendents
Land Move Adaptations

Charophyte algae inhabit shallow waters
Dessication is a problem
 Natural selection chose individuals that could survive


Sporopollenin is a polymer layer to prevent spores
from drying out during dispersal

Allowed 1st land plants to survive terrestrially


Needed to overcome challenges


Brighter sunlight, more CO2, and mineral rich
Scarce water and little structural support
4 adaptations specific to land plants

Not unique to (convergent evolution) and not all plants have
Alternation of Generations


Each generation gives rise to the
other
Gametophyte generation
 From
1n spore by mitosis
 Produce gametes by mitosis
 Gametes combine in syngamy to
form 2n zygote

Sporophyte generation
 From
2n zygote by mitosis
 Produces spores by meiosis

Generations can look different
 Plants
we see usually sporophyte
Other Derived Traits
* Apical meristems
Localized regions of
cell division at tips of
shoots and roots
* Walled spores
produced in sporangia.
Multicelled organs where
sporocytes (2n) produce
spores via meiosis.
* Multicellular gametangia
Archegonia: female, pearshape with non-motile egg
Antheridia: male, release
sperm to environment
Additional Characteristics


Epidermis covered by a cuticle to protect leaves
from desiccation
Early plants without true roots and leaves benefited
from mycorrhizal associations with fungi
 Review:

2 types are?
Secondary compound production to prevent against
herbivores, parasites, and UV radiation
 Human
 E.g
source of spices and medicines
tannin in red wines from grape skin, stem, and seed;
responsible to dry, pucker taste/sensation of good reds
Diversification of Plants
Nonvascular: unclear
monophylogeny
No vascular tissue, true
roots, stems, or leaves
Small, grow low, moist
environments
Vascular: exist in
smaller clades (phyla)
Seedless are
paraphyletic
Seeds are embryos with
nutrients in a protective
shell
Gymno: naked seeds
Angio: flowering plants
Nonvascular Plants

Phylum Hepatophyta (liverworts)
 Marchantia
has ‘thalloid’ shape gametophyte
 Gametangia
 Plagiochilla

appear as mini trees from which sporophytes hang
has ‘leafy’ looking gametophytes
Phylum Anthocerophyta (hormworts)
 Long,
tapered sporophyte with an open sporangium
 Gametophyte grows horizontally, 1st to colonize open area

Phylum Bryophyta (mosses)
 Mainly
see gametophyte stage, carpet-like
 Sporophytes visible and tall, green when young, tan to
release spores
Nonvascular Plants Life Cycle

Gametophyte is dominant
stages
Protonemata produce
‘buds’
 Develop into gametophores
with rhizoids = anchors
 Antheridia or archegonia
 Can be bi- (not mosses)


Sporophyte results
Dependent on parent
 Develop foot, stalk (seta),
and capsule (sporangium)

Importance of Mosses


Colonize bare, sandy soil and help retain nitrogen
Moist environments and extreme ones
 Mountaintops,


tundra, and deserts
Survive despite loss of water and rehydrate when
conditions improve
Sphagnum forms deposits of dead organic material
= peat
 Good
fuel
for water absorbing and gardening; dried as
Evolution of Seedless Vascular Plants

Sperm is flagellated like
nonvascular plants so must
move through films of water
to fertilize egg




Common in moist environments
Branched sporophytes not
dependent on gametophytes
for nutrition
Branching allowed for
multiple sporangia
Ancestors lacked roots, but
shared other traits
Seedless Vascular Plant Life Cycle



Compare with nonvascular life cycle
Sporophyte generation is larger and more complex
In ferns is what is seen


Gametophytes grow on or in soil
Gametophytes reduced as evolution to seed plants
Vascular Transport Tissue

Xylem conducts most water
and minerals




Usess tracheids (tubeshaped cells) to move root to
tip
Cell walls strengthened with
lignin, a polymer
Phloem distributes sugars,
amino acids, and other
organics through cells
arranged as tubes
Evolutionary adaptations


Taller
Cover other plants
(dominance)

Evolution of trees
Roots and Leaves Appear

Roots absorb from the soil and provide support
 Resemble

stem tissue
Leaves increase SA and serve as photosynthetic
organs
 Stomata
to regulate gas and water exchange
 Microphylls: small, spine-like leaves, single vascular
tissue
 Phylum
lycophyta only
 Megaphylls:
 More

highly branched vascular tissue
photosynthetic
Stems move water and minerals to leaves and
organics from leaves to roots
Sporophylls
Modified leaves
that bear
sporangia
Vary in structure
between phyla
of vascular
plants
Most seedless
vascular plants
are
homosporous
Phylum Lycophytes




Club mosses, spike
mosses, and quillworts
Sporophylls clustered
together as cone-like
structures called strobili
Club mosses all
homosporous while
others are heterosporous
Club moss spores are
rich in oil

Photographers ignited
them to create light

Previously represented as 3 separated phyla
All homosporous

Ferns




Sporophytes produce fronds that grow as fiddlehead uncoils
Gametophytes die after sporophyte detaches
Horsetails


Separate fertile (cone-bearing) and vegetative stems
Stems have joints with small leaves emerging from them


Stem is main photosynthetic organ
Whisk ferns


Sporophytes have branched stems, but no roots
3 fused sporangia on stems