Chapter 28 - Sadava Plants without Seeds: from Water to Land

Before we start Plants, a review…. Domain Archaea Prokaryotic, include extremophile bacteria Domain Bacteria Prokaryotic, includes what we knew as Kingdom Monera Domain Eukarya Eukaryotic Includes: Kingdom Fungi What we knew as Kingdom Protista (green algae are related to plants) Kingdom Plantae Kingdom Animalia

Land plants are monophyletic all descend from a single common ancestor One shared derived character a synapomorphy development from an embryo protected by tissues of the parent plant Why is this important on land? Also called embryophytes

Land plants retain derived features they share with green algae (which are protists): Chlorophyll a and b. Starch as a storage product. Cellulose in cell walls. Photo 28.2 Green algae of phylum Chlorophyta are most likely ancestors of plants.

“Plants” can be defined in several ways Streptophytes include land plants and a paraphyletic group of green algae —all retain egg within parent’s body Green plants: streptophytes plus all other green algae. All have chlorophyll b This textbook: “plants” refers only to land plants What we think of in Kingdom Plantae

Vascular plants, or tracheophytes 10 clades of land plants Vascular plants, or tracheophytes 7 clades all have conducting cells called tracheids The seven groups of vascular plants constitute a clade themselves Nonvascular plants 3 clades www.sonoma.edu/users/c/cannon/

Plants first appeared on land between 400–500 million years ago Adaptations were needed to survive in dry environments Large plants must transport water to all parts of plant Needed support in air Needed methods to disperse gametes

Characteristics of land plants: The cuticle (waxy lipids) Stomata – openings in stems and leaves; regulate gas exchange (except liverworts) Gametangia enclosing gametes Embryos in a protective structure Pigments that protect against UV radiation Spore walls containing sporopollenin Mutualistic relationships with fungi to promote nutrient uptake from soil

Alternation of generations All land plants have a life cycle with alternation of generations multicellular haploid (gametophyte) multicellular diploid (sporophyte) individuals

Alternation of generations Sporophyte Produces spores, all cells are diploid Cells in sporangia (in sporophyte) undergo meiosis to produce haploid, unicellular spores Spores are released Spore develops into multicellular haploid structure, the gametophyte Gametophyte Produces gametes, all cells are haploid Produce gametes by mitosis Fusion of egg and sperm results in diploid zygote Zygote develops into sporophyte

In plants that appeared later, this is reversed Reduction of the gametophyte generation is a major theme in plant evolution In nonvascular plants: gametophyte is larger, longer-lived, and more self-sufficient than the sporophyte Gametophyte is photosynthetic In plants that appeared later, this is reversed In seed vascular plants (gymnosperms and angiosperms), sporophyte generation is dominate Sporophyte is photosynthetic Gametophyte might only be a few cells it is so small

Nonvascular plants Do not have vascular tissue liverworts, hornworts, and mosses These groups do not form a clade – why?

In nonvascular plants, the gametophyte generation is photosynthetic Sporophytes may or may not be photosynthetic,… but are always nutritionally dependent on gametophyte, and is permanently attached Sporophytes arising from gametophytes Gametophytes http://taggart.glg.msu.edu/bot335/MOSS.GIF

Haploid gametophyte produces gametes in specialized sex organs (gametangia) Female: archegonium  produces one egg Male: antheridium  produces many sperm with two flagella each Archegonium Antheridium Flagellated moss sperm http://www.dkimages.com/discover/previews/832/20113674.JPG

Nonvascular plants Sperm must swim to archegonium, or be splashed by raindrops Egg or archegonium releases chemical attractants for sperm Water is required for all these events

Vascular Plants Vascular plants include the club mosses, ferns, conifers, and angiosperms (flowering plants). True roots and leaves

What Features Distinguish the Vascular Plants? The vascular system consists of tissue specialized for transport of materials Xylem conducts water and minerals from soil up to aerial parts of plant. Some cells have lignin — provides support Phloem conducts products of photosynthesis through plant. http://plantandsoil.unl.edu/croptechnology2005/UserFiles/Image/siteImages/Fig-3-large.gif

First plant fossils are from Silurian (408-440 mya) Tracheids are main water-conducting element in xylem Evolution of tracheids in plants set stage for invasion of land First plant fossils are from Silurian (408-440 mya) Made land more hospitable for animals Amphibians and insects arrived soon after plants www.unlv.edu/Colleges/Sciences/Biology/Schulte/Anatomy/CellsTissues

Vascular plants also have a large, branching, independent sporophyte Mature sporophyte is nutritionally independent from gametophyte Fern prothallus Small independent gametophyte (left) and branched sporopythe (right) of ferns http://virtual.yosemite.cc.ca.us/randerson/Lynn's%20Bioslides/20.jpg http://web.cortland.edu/broyles/hayg

Vascular plants Euphyllophytes “true leaf plants” Includes: Monilophytes – seedless vascular plants that have megaphylls seed plants (gymnosperms and flowering plants) Synapomorphies include overtopping growth — new branches grow beyond the others —an advantage in the competition for light

True leaves evolved flattened photosynthetic structures arising from a stem or branch has true vascular tissue two types Microphylls – small, one vascular strand Club mosses have these Megaphylls

Heterosporous vascular plants produce two types of spores: Megaspores develop into female gametophytes — megagametophyte Megaspores are produced in small numbers in megasporangia Microspores develop into male gametophytes — microgametophyte Microspores are produced in large numbers in microsporangia

Nonvascular seedless land plants: three clades: liverworts mosses hornworts

Embryophytes Nonvascular Seedless plants Hepatophyta Liverworts: Hepatophyta Sporophytes very short Remember that gametophyte generation is dominant in nonvascular plants Can reproduce asexually Do so by dispersing gemmae which are in gemmae cups www.bcbiodiversity.homestead.com/files

Embryophytes Nonvascular Seedless plants Bryophyta The mosses: Bryophyta Mosses (plus hornworts and vascular plants) have stomata important in water & gas exchange

Embryophytes Nonvascular Seedless plants Anthocerophyta Hornworts: Anthocerophyta Gametophytes are flat plates of cells Have stomata, which do not close http://www.botany.org/PlantImages/Conant/CA06-014_300.jpg

Seedless Vascular Plants Seedless VASCULAR plants – three monophyletic clades: club mosses horsetails whisk ferns plus ferns and allies (not monophyletic, though 97% are)

Seedless Vascular Plants Small, short-lived gametophyte is independent of the large sporophyte Single-celled spore is resting stage Can grow larger because of vascular tissue but must have water for part of life cycle — for the flagellated, swimming sperm www.biologie.uni-hamburg.de/b-online/library/webb/BOT311/FERNS

Embryophytes Seedless Vascular Plants Lycophytes Lycophytes: club mosses, spike mosses, and quillworts Roots and stems have dichotomous branching Leaves are microphylls Strobilli – clusters of sporangia Lycopodium annotinum http://ip30.eti.uva.nl/bis/flora/pictures

Embryophytes Seedless Vascular Euphyllophytes Monilophytes Monilophytes (a.k.a. Pteridophytes) — horsetails, whisk ferns, and ferns & allies, form a clade Horsetails and whisk ferns are both monophyletic, but ferns are not But 97% of ferns form a clade — the leptosporangiate ferns

Embryophytes Seedless Vascular Euphyllophytes Monilophytes Horsetails 15 species in one genus — Equisetum Silica in cell walls — “scouring rushes”… used for cleaning Equisetum hymale www.plantoftheweek.org/image

Embryophytes Seedless Vascular Euphyllophytes Monilophytes Whisk ferns 15 species in two genera No roots but well-developed vascular system Psilotum nudum http://www.botanik.uni-karlsruhe.de/garten/fotos-knoch/Psilotum%20nudum%20Gabelblatt%201.jpg

Embryophytes Seedless Vascular Euphyllophytes Monilophytes Sporangia occur on undersides of leaves in clusters called sori http://departments.bloomu.edu/biology/pics/botany/fern_sori2w.jpg

Monilophytes (Pteridophytes) – Ferns Fern gametophytes produce antheridia and archegonia, not always at same time or on same gametophyte www.esu.edu/~milewski/intro_biol_two/lab_2_moss_ferns

Embryophytes Seedless Vascular Euphyllophytes Monilophytes Most ferns found in shaded, moist environments Tree ferns can reach heights of 20 m Dixie Woods fern, Dryopteris australis Tree ferns http://www.wettropics.gov.au/st/rainforest_explorer/Resources/Images/plants/TreeFerns.jpg http://www.we-du.com/images/plants/350/frndrydwf.jpg