Seedless Plants Chapter 30

Origin of Land Plants 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 are excluded A single species of freshwater green algae gave rise to the entire terrestrial plant lineage

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

Green plants Streptophyta Land plants Bryophytes Tracheophytes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Green plants Streptophyta Land plants Bryophytes Tracheophytes Euphyllophytes Green algae Green algae Seed plants Red Algae Chlorophytes Charophytes Liverworts Mosses Hornworts Lycophytes Ferns + Allies Gymnosperms Angiosperms Ancestral alga

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

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

n 2n MITOSIS MEIOSIS FERTILIZATION Gametophyte (n) Spore Sperm n n Egg Spore mother cell 2n Zygote Sporangia 2n Embryo Sporophyte (2n)

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

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

Simple, but highly adapted to diverse terrestrial environments 24,700 species in 3 clades Liverworts Mosses Hornworts Gametophyte – conspicuous and photosynthetic Sporophytes – small and dependent Require water for sexual reproduction

Liverworts (phylum Hepaticophyta) Have flattened gametophytes with liverlike lobes 80% look like mosses Form gametangia in umbrella-shaped structures Also undergo asexual reproduction Female gametophyte © David Sieren/Visuals Unlimited

Leafy vs Thallose Liverworts

Leafy vs Thallose Liverwort

Marchantia polymorpha

Liverwort Sex… (if you are under 18, please close your eyes!) Click here for XXX rated liverwort porn

Moss grows on the north side of a tree… Mosses Moss grows on the north side of a tree…

“Haircap Moss”, Polytrichum

Hair Cap Moss

Apple Moss, Bartramia

Pin Cushion Moss, Leucobryum

Delicate Fern Moss, Thuidium

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

Sporophyte Gametophyte Male Gametophytes Sperm Egg Antheridia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Male Gametophytes Sperm Egg Antheridia Archegonia FERTILIZATION Female Germinating spores Rhizoids Sporophyte Zygote n 2n MITOSIS MITOSIS Gametophyte Spores Mature sporophyte 2n 1n MIEIOSIS Developing sporophyte in archegonium 2n Sporangium Parent gametophyte 1n

Hornworts (phylum Anthocerotophyta) Origin is puzzling – no fossils until Cretaceous Sporophyte is photosynthetic Sporophyte embedded in gametophyte tissue Cells have a single large chloroplast Photosynthetic sporophyte

Tracheophyte 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 Sporangia

Vascular tissues Xylem Phloem 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

Tracheophytes Vascular plants include seven extant phyla grouped in three clades Lycophytes (club mosses) Pterophytes (ferns, whisk ferns, and horsetails) 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

Stems Roots Leaves 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

without vascular tissue Photosynthetic tissue Lycophyll Origins Single vascular strand (vein) Stem with vascular tissue Stem, leafy tissue without vascular tissue Stem, leafy tissue with vascular tissue Euphyll Origins Branched vascular strands (veins) Branching stems with vascular tissue Unequal branching Branches in single planes Photosynthetic tissue “webs” branches

400 million years between appearance of vascular tissue and true leaves Natural selection favored plants with higher stomatal densities in low-CO2 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

Chlorophytes Charophytes Liverworts Mosses Hornworts Lycophytes Ferns + Allies Gymnosperms Angiosperms Flowers Fruits Seeds Euphylls Stems, roots, leaves Dominant sporophyte Vascular tissue Stomata Multicellular embryo Antheridia and archegonia Cuticle Plasmodesmata Chlorophyll a and b Ancestral alga 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

Lycophytes Worldwide distribution – abundant in tropics Lack seeds Ferns and Allies Seed Plants Hornworts Lycophytes Lycophytes Worldwide distribution – abundant in tropics Lack seeds Superficially resemble true mosses Sporophyte dominant 15 PA species

Princess Pine Dendrolycopodium obscurum

Shining Club Moss Lycopodium lucidulum

Ground Pine

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 Horsetail Ferns Lycophytes Whisk Ferns Seed Plants Ferns Ferns

Whisk Ferns Found in tropics, none locally Sporophyte consists of evenly forking green stems without true leaves or roots (found to be monophyletic with ferns) Some gametophytes develop elements of vascular tissue Only gametophytes known to do so

Horsetails All 15 living species are homosporous Constitute a single genus, Equisetum; 5 species in PA Sporophyte consists of ribbed, jointed photosynthetic stems that arise from branching rhizomes with roots at nodes Silica deposits in cells – scouring rush

Ferns

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

Fern life cycle differs from that of a moss Antheridium Archegonium Rhizoids Fern life cycle differs from that of a moss Much greater development, independence, and dominance of the fern’s sporophyte Gametophyte lacks vascular tissue Archegonium Egg Sperm Gametophyte MITOSIS Antheridium FERTILIZATION Spores MEIOSIS 1n Zygote 2n n 2n MITOSIS Underside of leaf frond Mature frond Leaf of young sporophyte Adult sporophyte Embryo Mature sporangium Sorus (cluster of sporangia) Gametophyte Sporangium Rhizome

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

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

sterile frond fertile frond fiddlehead/crozier rhizome

Ferns

Pinnate Pinnatifid

Not everything that looks like a fern is one!

…and not everything that is a fern looks like one!

Matteuccia struthiopteris Ostrich Fern Matteuccia struthiopteris separate fertile and vegetative fronds

Sensitive Fern Onoclea sensibilis

Dennstaedtia punctilobula Hay-scented Fern Dennstaedtia punctilobula