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Chapter 26: The Plant Kingdom: Seedless Plants
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Charophytes Green algae Closest ancestor to plants Evidence
Charales and Coleochaetes
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5 mm 40 µm Chara species, a pond organism Coleochaete orbicularis, a
Fig. 29-3 Chara species, a pond organism 5 mm Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) Figure 29.3 Examples of charophytes, the closest algal relatives of land plants 40 µm
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Features of Charophytes that promoted evolution of multicellular land plants
1) Cellulose synthesizing complexes nearly identical (during cell wall formation) 2) Apical cells – allow filaments to increase in length 3) Plasmodesmata – communication between neighboring cells 4) Both retain and care for zygote
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Adaptations to Life on Land
Cuticle Waxy, aerial, prevents desiccation Stomata Pores on surface of leaves, stems Gas exchange Gametangia Multicellular sex organs Embryo develops within female gametangium (protected)
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7 Characteristics of Plants
Multicellular, eukaryotic Photosynthetic Waxy cuticle Terrestrial Stomata and guard cells Complex fertilization Cell walls of cellulose and lignin
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Alternation of Generations
Switch between haploid and diploid Both multicellular Dominant generation Haploid (n) = gametophyte Mitosis – haploid gametes Antheridia – sperm Archegonia - egg Diploid (2n) = sporophyte Meiosis – haploid spores Zygote (sperm + egg) multicellular embryo (in archegonium)
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Placental transfer cell (outlined in blue)
Fig. 29-5b Embryo 2 µm Maternal tissue Figure 29.5 Derived traits of land plants Wall ingrowths 10 µm Placental transfer cell (outlined in blue) Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort)
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Alternation of generations
Fig. 29-5a Gamete from another plant Gametophyte (n) Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION Zygote 2n Figure 29.5 Derived traits of land plants Mitosis Sporophyte (2n) Alternation of generations
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Fertilization zygote embryo mature sporophyte sporogenous cells meiosis spores mature gametophyte archegonia or antheridia egg/sperm
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Check your Understanding
1. What are the benefits of a lands existence for plants? 2. What traits are shared by both charophytes and land plants? 3. What is the role of each generation in the alternation of generations life cycle?
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4 Major Plant Groups Bryophytes Ferns Gymnosperms Angiosperms
Small, nonvascular, seedless, use haploid spores Ferns Seedless, vascular, spores Gymnosperms Vascular, seeds (unprotected) Angiosperms Vascular, flowering, seed in a fruit
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Figure 29.7 Highlights of plant evolution
1 Origin of land plants (about 475 mya) 2 Origin of vascular plants (about 420 mya) 3 Origin of extant seed plants (about 305 mya) Liverworts Nonvascular plants (bryophytes) Land plants ANCES- TRAL GREEN ALGA 1 Hornworts Mosses Lycophytes (club mosses, spike mosses, quillworts) Seedless vascular plants 2 Vascular plants Pterophytes (ferns, horsetails, whisk ferns) Figure 29.7 Highlights of plant evolution Gymnosperms 3 Seed plants Angiosperms 500 450 400 350 300 50 Millions of years ago (mya)
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Mosses and other Bryophytes
Nonvascular – so small Mosses, liverworts, hornworts Moist environment – growth and reproduction 3 phyla Bryophyta Hepaticophyta Anthocerotophyta
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Mosses - Bryophyta Dense colonies or beds Individual plant
Rhizoids (absorb) Upright, stem like Leaf like blades No true roots, stems or leaves Alternation of generations 3 groups: peat moss, granite moss, true moss
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Polytrichum commune, hairy-cap moss Sporophyte (a sturdy Capsule
Fig. 29-9d Polytrichum commune, hairy-cap moss Sporophyte (a sturdy plant that takes months to grow) Capsule Seta Figure 29.9 Bryophyte diversity Gametophyte
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Figure 29.8 The life cycle of a moss
Raindrop Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n) Protonemata (n) Diploid (2n) “Bud” Egg Spores Gametophore Archegonia Spore dispersal Female gametophyte (n) Rhizoid Peristome Sporangium FERTILIZATION Figure 29.8 The life cycle of a moss MEIOSIS (within archegonium) Seta Zygote (2n) Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium Young sporophyte (2n) 2 mm Capsule with peristome (SEM) Female gametophytes
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Moss Gametophyte
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Moss spores
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Moss protonema
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Marchantia polymorpha, a “thalloid” liverwort
Fig. 29-9a Gametophore of female gametophyte Thallus Sporophyte Foot Seta Figure 29.9 Bryophyte diversity Capsule (sporangium) Marchantia polymorpha, a “thalloid” liverwort 500 µm Marchantia sporophyte (LM)
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Moss importance Ecological Commercial Form soil, prevent erosion
Rainforest beauty Commercial Peat moss (sphagnum) Absorb and hold water Soil conditioner – add to sand Fuel source – if dried
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(a) Peat being harvested
Fig a Figure Sphagnum, or peat moss: a bryophyte with economic, ecological, and archaeological significance (a) Peat being harvested
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Liverworts - Hepaticophyta
Dominant gametophyte Thallus – body – flattened, lobed No leaves, stems, roots Resemble lobes of liver Underside – rhizoids – anchor No stomata – some surface pores Others Leafy liverworts – no lobes
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THALLOID Liverwort
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Plagiochila deltoidea, a “leafy” liverwort Fig. 29-9b
Figure 29.9 Bryophyte diversity
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Basics of liverwort life cycle
Sexual - Similar to mosses Asexual Form gemmae in gemmae cup
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Hornworts - Anthocerotophyta
Inconspicuous thalloids Disturbed habitats – fallow fields, roadsides Cell structure – single chloroplast Sporophyte projects out of thallus like horn
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An Anthoceros hornwort species Sporophyte Gametophyte Fig. 29-9c
Figure 29.9 Bryophyte diversity Gametophyte
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Lycophytes: Vascular Tissue
Seedless vascular plants Stems, roots, leaves Conducting cells Lignin Cooksonia = rhyniophyte Microphylls Club mosses
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Club mosses - Lycophyta
Coal deposits True roots, rhizomes, aerial stems Short, erect branches Evergreen
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Lycophytes (Phylum Lycophyta)
Fig a Lycophytes (Phylum Lycophyta) 2.5 cm Isoetes gunnii, a quillwort Strobili (clusters of sporophylls) Selaginella apoda, a spike moss Figure Seedless vascular plant diversity 1 cm Diphasiastrum tristachyum, a club moss
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Lycophyte
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CYU 1. Name two features of lycophytes significant to the evolution of land plants.
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Seedless Vascular Plants – Pterophyta (Pteridophytes)
Ferns, horsetails, whisk ferns Adaptations Vascular – xylem and phloem Support Conduction larger Most – true roots, stems, leaves Megaphylls
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Ferns Most abundant – warm, tropics True roots, stems, leaves Fronds
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Athyrium filix-femina, lady fern 25 cm Fig. 29-15f
Figure Seedless vascular plant diversity 25 cm
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Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte
Fig Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Sporangium Mature gametophyte (n) Sperm Archegonium Egg Mature sporophyte (2n) Sporangium New sporophyte Zygote (2n) FERTILIZATION Sorus Figure The life cycle of a fern Gametophyte Fiddlehead
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Fern Sorus
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Fern – Older sporangium
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Fern germinating
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Fern Gametophyte
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CYU How is the life cycle of a fern different from the life cycle of a moss?
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Whisk ferns - Psilotophyta
Simplest vascular Stems – horizontal underground Vertical aerial - photosynthesize Lack true roots, leaves Dichotomous branching – stem divides into 2 equal halves
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Psilotum nudum, a whisk fern 2.5 cm Fig. 29-15h
Figure Seedless vascular plant diversity 2.5 cm
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Horsetails - Sphenophyta
Ancient – coal deposits Wet, marshy True roots (rhizome), stems (aerial), small leaves Hollow, jointed stems – silica – gritty Scouring rushes – pots/pans
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Equisetum arvense, field horsetail Vegetative stem Strobilus on
Fig g Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem Figure Seedless vascular plant diversity 1.5 cm
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Horsetail
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Homospory – meiosis produces 1 type of spore
Heterospory – meiosis produces 2 different spore types: microspores and megaspores Microsporangia – produce microsporocytes meiosis haploid microspores male gametophyte sperm cells in antheridia Megasporangia – make megasporocytes meiosis haploid megaspores female gametophyte eggs in archegonia
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Homosporous spore production
Fig. 29-UN3 Homosporous spore production Typically a bisexual gametophyte Eggs Sporangium on sporophyll Single type of spore Sperm Heterosporous spore production Megasporangium on megasporophyll Female gametophyte Megaspore Eggs Microsporangium on microsporophyll Microspore Male gametophyte Sperm
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You should now be able to:
Describe four characteristics of plants Distinguish between the phylum Bryophyta and bryophytes Diagram and label the life cycle of a bryophyte Explain why most bryophytes grow close to the ground and are restricted to periodically moist environments
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Explain how vascular plants differ from bryophytes
Distinguish between homosporous and heterosporous Diagram and label the life cycle of a seedless vascular plant
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