CHAPTER 29: PLANT DIVERSITY How Plants Colonized Land By: Meg Riley, Anna Ferlanti, and Laurie VanBenschoten

The Greening of Earth  Land plants evolved from aquatic green algae 500 mya  Plants are crucial to life on Earth  Supply Oxygen  Provide Habitats  Provide Food Charophyceans (algal ancestor of land plants)

Evolution from Algae  Aquatic green algae= charophyceans  closet living relative of land plants, share a common ancestor  First land plants were seedless  reproduced using spores

Evidence for Common Ancestry  Morphological and Biochemical Evidence  Structure of flagellated sperm Closely resembles that of charophyceans  Genetic Evidence  Nuclear & chloroplast genes suggest relatedness to charophyceans Confirms conclusions from above

Adaptations for Movement to Land  Adaptations enabling the Move to Land  A chemical found in both charophyceans & land plants Plants encases spores Algae prevents zygote from drying out in exposed environments

The Plant Kingdom  Kingdom Plantae currently includes all embryophytes  Embryophytes= plants that grow from an embryo excludes charophyceans

Derived Traits of Land Plants  These traits, unique to nearly all plants, distinguish them from charophyceans  Apical meristems- localized regions of cell division that make vascular tissue  Alternation of generations- alternation between two multicellular body forms between generations  Walled spores produced in sporangia- multicellular capsules that contain and protect spores during development  Multicellular gametangia- multicellular organs in which gametes are produced Archegonia- female, 1 egg Antheridia- male, many sperm  Multicellular, dependent embryos- zygote retained within tissue of female parent and develops with nutrients from mother  Cuticle coverings- layer of polyesters & waxes that prevents plant from drying- out ***(see pg for full explanations)

Evolutionary History of Land Plants

Gametophyte vs. Sporophyte Gametophyte multicellular haploid form of a cell undergoing alternation of generations 1n Sporophyte multicellular diploid form of a cell undergoing alternation of generations 2n VS.

Characteristics of Bryophytes  Bryophytes are seedless nonvascular plants  found in three plant phyla…phylum Hepatophyta (liverworts), Anthocerophyta (hornworts), and Bryophyta (aka moss)  Gametophyte is dominant over sporophyte  Bryophyte Gametophytes  Characteristics Form ground-hugging carpets, low to the ground, short Thin, approx. 1 cell layer thick  Bryophyte Sporophytes  Consist of 3 parts: Foot- anchors to set into sporophyte Seta (or stalk)- holds up sporangium Sporangium (or capsule)- contains & protects spores  Ecological and Economic importance of Mosses  Mosses are widespread and important Ex. Peat moss used as fossil fuel and good for preserving bodies in swamps

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Life Cycle of Bryophyte (ex. Moss)  Spores develop into threadlike strands of plant fibers  The haploid strands produce “buds” that grow into gametophytes  Most mosses have separate male and female gametophytes with antheridia and archegonia respectively  A sperm swims through a film of moisture to an archegonium and fertilizes the egg  The diploid zygote develops into a sporophyte embryo within the archegonium  The sporophytes grows a long stalk, or seta, that emerges from the archegonium  Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte  Meiosis occurs and haploid spores develop in the sporangium of the sporophyte  Sporangium pops off, propelling spores into the air using “teeth”

Characteristics of Lycophytes & Pterophytes  Origins and Traits of Vascular Plants  Life Cycles with Dominant Sporophytes More sporangia, more spores, more evolutionarily fit to survive into adulthood  Transport in Xylem and Phloem (type of vascular tissue) Xylem-conducts water & minerals Phloem- conducts sugar, amino acids, and other organic products  Evolution of Roots Roots –anchor plant, allow for absorption of water and nutrients from soil  Evolution of Leaves Leaves- increase surface area, allow capture of more sunlight for photosynthesis, increase plant efficiency Mircohpylls- leaves of old lycophytes Megaphylls- leaves of new lycophytes, more complex

Characteristics of Seedless Vascular Plants (cont.)  Sporophylls and Spore Variations Sporophylls (modified leaves with sporangia) Homosporous vs. Heterosporous Megaspores vs. Microspores

Life Cycle of a Lycophyte (ex. Fern)  Sporangia release spores  Spore develops into photosynthetic gametophyte  Cross or self- fertilization may occur between male and female gametes  Sperm use flagella to swim from antheridium to archegonium  Sporophyte grow out of archegonium of gametophyte  Spores form in clusters on underside of reproductive leaves (sorus)

Classification  Phylum Lycophyta: older seedless vascular plants, common ones include spike & club mosses (not true mosses)  Phylum Pterophyta: younger seedless vascular, all sorts of ferns Spike/Club MossFern

Significance  How evolution of vascular tissue, roots, and leaves allows plants to grow bigger than ever before…development of large forests  Increased removal of CO2 from atmosphere, resulting in global cooling  Plants fossilize to from coal, however, once coal is burned as fossil fuels, it results in global warming

Answers to Activity:  Part 1- Moss  Part 2- Fern