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 Proteins in the PM that synthesize cellulose in cell wall

Peroxisome enzymes Help minimize loss of organic products from

photorespiration Flagellated sperm structure

Similar structure in land plants with and charophyceans

Formation of a phragmoplast 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

Brighter sunlight, more CO2, and mineral rich Needed to overcome challenges

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

* Walled spores produced in sporangia.

Multicelled organs where sporocytes (2n) produce spores via meiosis.

* Multicellular gametangia

Archegonia: female, pear-shape with non-motile eggAntheridia: male, release sperm to environment

* Apical meristems

Localized regions of cell division at tips of shoots and roots

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 source of spices and medicines

E.g tannin in red wines from grape skin, stem, and seed; responsible to dry, pucker taste/sensation of good reds

Diversification of PlantsNonvascular: 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 appear as mini trees from which sporophytes hang Plagiochilla 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 for water absorbing and gardening;

dried as fuel

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 (tube-

shaped 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: highly branched vascular tissue More 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