All green algae and the land plants shared a common ancestor a little over 1 BYA Kingdom Viridiplantae Not all photoautotrophs are plants Red and brown algae excluded A single species of freshwater green algae gave rise to the entire terrestrial plant lineage 2

Origin of Land Plants The green algae split into two major clades Chlorophytes – Never made it to land Charophytes – Sister to all land plants Land plants … Have multicellular haploid and diploid stages Trend toward more diploid embryo protection Trend toward smaller haploid stage 3

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ancestral alga ChlorophytesCharophytesLiverwortsHornwortsMossesLycophytesGymnospermsAngiosperms Seed plants Euphyllophytes Bryophytes Land plants Streptophyta Green plants Green algae Red Algae Tracheophytes Ferns + Allies

Adaptations to terrestrial life 1. Protection from desiccation Waxy cuticle and stomata 2. Moving water using tracheids – specialize cell Tracheophytes have tracheids Xylem and phloem to conduct water and food 3. Dealing with UV radiation caused mutations Shift to a dominant diploid generation 4. Haplodiplontic life cycle Mulitcellular haploid and diploid life stages Humans are diplontic 5

Haplodiplontic Life Cycle Multicellular diploid stage – sporophyte Produces haploid spores by meiosis Diploid spore mother cells (sporocytes) undergo meiosis in sporangia Produce 4 haploid spores First cells of gametophyte generation Multicellular haploid stage – gametophyte Spores divide by mitosis Produces gametes by mitosis Gametes fuse to form diploid zygote First cell of next sporophyte generation 6

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Spore n n n n Spore mother cell 2n2n Sporangia Sporophyte (2n) 2n2n 2n2n Zygote Embryo Egg Sperm MEIOSIS MITOSIS FERTILIZATION n 2n2n Gametophyte (n)

All land plants are haplodiplontic Relative sizes of generations vary Moss Large gametophyte Small, dependent sporophyte Angiosperm Small, dependent gametophyte Large sporophyte 8

Bryophytes Closest living descendants of the first land plants Called nontracheophytes because they lack tracheids Do have other conducting cells 9 Mycorrhizal associations important in enhancing water uptake –Symbiotic relationship between fungi and plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Charophytes Liverworts Mosses Hornworts Tracheophytes

Ex 1: Liverworts (phylum Hepaticophyta) Have flattened gametophytes with liverlike lobes 80% look like mosses Form gametangia in umbrella-shaped structures Also undergo asexual reproduction 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Female gametophyte © David Sieren/Visuals Unlimited

Ex2: Mosses (phylum Bryophyta) Gametophytes consist of small, leaflike structures around a stemlike axis Not true leaves – no vascular tissue Anchored to substrate by rhizoids Multicellular gametangia form at the tips of gametophytes Archegonia – Female gametangia Antheridia – Male gametangia Flagellated sperm must swim in water 11

12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Edward S. Ross Sporophyte Gametophyte Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. n 2n2n 2n2n 2n2n 1n1n 1n1n Sperm Sporangium Antheridia Egg Archegonia Gametophytes Spores Rhizoids Female Male Zygote MITOSIS FERTILIZATION Mature sporophyte Developing sporophyte in archegonium Parent gametophyte MITOSIS MIEIOSIS Germinating spores Ex: Mosses (phylum Bryophyta)

Ex 3: Hornworts (phylum Anthocerotophyta) Origin is puzzling – no fossils until Cretaceous Sporophyte is photosynthetic Sporophyte embedded in gametophyte tissue Cells have a single large chloroplast 13 Photosynthetic sporophyte Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Lee W. Wilcox

Tracheophyte Plants Known as vascular plants Cooksonia, the first vascular land plant Appeared about 420 MYA Phylum Rhyniophyta Only a few centimeters tall No roots or leaves Homosporous – only 1 type of spore 14 Sporangia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Vascular tissues Xylem Conducts water and dissolved minerals upward from the roots Phloem Conducts sucrose and hormones throughout the plant Enable enhanced height and size in the tracheophytes Develops in sporophyte but not gametophyte Cuticle and stomata also found in land plants 15

Tracheophytes Vascular plants include seven extant phyla grouped in three clades 1. Lycophytes (club mosses) 2. Pterophytes (ferns, whisk ferns, and horsetails) 3. Seed plants Gametophyte has been reduced in size relative to the sporophyte during the evolution of tracheophytes Similar reduction in multicellular gametangia has occurred as well 16

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Stems Early fossils reveal stems but no roots or leaves Lack of roots limited early tracheophytes Roots Provide transport and support Lycophytes diverged before true roots appeared Leaves Increase surface area for photosynthesis Evolved twice Euphylls (true leaves) found in ferns and seed plants Lycophylls found in seed plants 18

19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Euphyll Origins Lycophyll Origins Stem with vascular tissue Stem, leafy tissue without vascular tissue Stem, leafy tissue with vascular tissue Single vascular strand (vein) Branched vascular strands (veins) Photosynthetic tissue “webs” branches Branches in single planes Unequal branching Branching stems with vascular tissue

400 million years between appearance of vascular tissue and true leaves Natural selection favored plants with higher stomatal densities in low-CO 2 atmosphere Higher stomatal densities favored larger leaves with a photosynthetic advantage that did not overheat Seeds Highly resistant Contain food supply for young plant Lycophytes and pterophytes do not have seeds 20

Fruits in the flowering plants (angiosperms) add a layer of protection to seeds and attract animals that assist in seed dispersal, expanding the potential range of the species 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ancestral alga ChlorophytesCharophytesLiverwortsHornwortsMossesLycophytesGymnospermsAngiosperms Chlorophyll a and b Plasmodesmata Cuticle Antheridia and archegonia Multicellular embryo Stomata Euphylls Seeds Flowers Fruits Dominant sporophyte Stems, roots, leaves Ferns + Allies Vascular tissue

Lycophytes Worldwide distribution – abundant in tropics Lack seeds Superficially resemble true mosses Sporophyte dominant 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. HornwortsLycophytesSeed Plants Ferns and Allies

Pterophytes Phylogenetic relationships among ferns and their relatives is still being sorted out Common ancestor gave rise to 2 clades All form antheridia and archegonia All require free water for flagellated sperm 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lycophytes FernsHorsetail FernsFernsWhisk Ferns Seed Plants

Whisk ferns Found in tropics Sporophyte consists of evenly forking green stems without true leaves or roots Some gametophytes develop elements of vascular tissue Only one known to do so 24

Horsetails All 15 living species are homosporous Constitute a single species, Equisetum Sporophyte consists of ribbed, jointed photosynthetic stems that arise from branching rhizomes with roots at nodes Silica deposits in cells – scouring rush 25

Ferns Most abundant group of seedless vascular plants About 11,000 species Coal formed from forests 300 MYA Conspicuous sporophyte and much smaller gametophyte are both photosynthetic 26

Fern life cycle differs from that of a moss Much greater development, independence, and dominance of the fern’s sporophyte Gametophyte lacks vascular tissue 27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MEIOSIS n 2n2n Archegonium Antheridium Egg Sperm Embryo 1n1n Gametophyte Rhizome Sporangium Spores Rhizoids Gametophyte MITOSIS Underside of leaf frond Mature sporangium Sorus (cluster of sporangia) Adult sporophyte Mature frond Leaf of young sporophyte MITOSIS Zygote 2n FERTILIZATION

Fern morphology Sporophytes have rhizomes Fronds (leaves) develop at the tip of the rhizome as tightly rolled-up coils (“fiddleheads”) 28 Tightly Coiled FernUncoiling Fern (left): © Mike Zens/Corbis; (right): © Ed Reschke Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fern reproduction Produce distinctive sporangia in clusters called sori on the back of the fronds Diploid spore mother cells in sporangia produce haploid spores by meiosis Spores germinate into gametophyte Rhizoids but not true roots – no vascular tissue Flagellated sperm 29