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 1 st land plants to survive terrestrially Brighter sunlight, more CO 2, 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 egg Antheridia: 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 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 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, 1 st 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