Plant Diversity I How Plants Colonized Land Chapter 29 Plant Diversity I How Plants Colonized Land

Concept 29.1: Land plants evolved from green algae Green algae called charophyceans are the closest relatives of land plants

Morphological and Biochemical Evidence Four key traits only with charophyceans: Rose-shaped complexes for cellulose synthesis Peroxisome enzymes Structure of flagellated sperm Formation of a phragmoplast

Coleochaete orbicularis, a disk-shaped charophycean (LM). Chara, a pond organism (LM). 10 mm 40 µm Coleochaete orbicularis, a disk-shaped charophycean (LM).

Advantages to Living on Land Increased sunlight unfiltered by water More Carbon Dioxide available Soil Rich in Nutrients Fewer Predators

Problems to Overcome Lack of water Dessication SPOROPOLLENIN: polymer prevents spores from drying out. CUTICLE: waxy layer on epidermis Lack of structural support against gravity

Derived Traits of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans: Apical meristems Alternation of generations Walled spores produced in sporangia Multicellular gametangia Multicellular dependent embryos

Apical Meristems LE 29-5a Apical Meristem of shoot Developing leaves Root 100 µm 100 µm

Alternation of Generations LE 29-5b Alternation of Generations Haploid multicellular organism (gametophyte) Mitosis Mitosis Spores Gametes MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (sporophyte)

ALTERNATION OF GENERATIONS HAPLOID GAMETOPHYTE undergoes MITOSIS to produce 1n Gametes (Sperm or Egg) FERTILIZATION to make DIPLOID ZYGOTE ZYGOTE develops into DIPLOID SPOROPHYTE SPOROPHYTE (2n) undergoes MEIOSIS to produce HAPLOID SPORES SPORES (1n) develop into HAPLOID GAMETOPHYTE SPORES are produced in SPORANGIA

ALTERNATION OF GENERATIONS continued. GAMETANGIA: multicellular organs in which gametes are produced. MALE gametangia= ANTHERIDIA- make sperm FEMALE gametangia = ARCHEGONIUM- make single egg

Walled Spores Produced in Sporangia Multicellular Gametangia LE 29-5c Walled Spores Produced in Sporangia Multicellular Gametangia Multicellular, Dependent Embryos Longitudinal section of Sphagnum sporangium (LM) Archegonium with egg Female gametophyte Spores Embryo Maternal tissue Sporangium 2 µm 10 µm Sporophyte Male gametophyte Antheridium with sperm Gametophyte Wall ingrowths Placental transfer cell Sporophyte and sporangium of Sphagnum (a moss) Archegonia and antheridia of Marchantia (a liverwort)

Additional derived traits such as a cuticle and secondary compounds evolved in many plant species

4 Main GROUPS OF PLANTS: Seedless Nonvascular Seedless Vascular Vascular with Naked Seeds Vascular with Seeds *** Vascular Plants - Tracheophytes

Seedless vascular plants Origin of vascular plants Land plants Vascular plants Bryophytes Seedless vascular plants Seed plants Gymno- sperms Angio- sperms Liverworts Hornworts Mosses Lycophytes Pterophytes Charophyceans Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga

1) Seedless Non Vascular (no xylem or phloem) Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants: Liverworts, Hornworts, Mosses,

Bryophyte Gametophytes In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time Animation: Moss Life Cycle

LE 29-8 Raindrop Key Male gametophyte Haploid (n) Sperm Diploid (2n) Spores develop into threadlike protonemata. “Bud” A sperm swims through a film of moisture to an archegonium and fertilizes the egg. Antheridia The haploid protonemata produce “buds” that grow into gametophytes. Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. Protonemata “Bud” Egg Spores Gametophore Female gametophyte Archegonia Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores. Rhizoid Peristome Sporangium The sporophyte grows a long stalk, or seta, that emerges from the archegonium. FERTILIZATION MEIOSIS (within archegonium) Seta Calyptra Capsule (sporangium) Zygote Mature sporophytes Foot Embryo Archegonium The diploid zygote develops into a sporophyte embryo within the archegonium. Young sporophyte Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. Capsule with peristome (SEM) Female gametophytes

Bryophyte gametophytes Produce flagellated sperm in antheridia Produce ova in archegonia Generally form ground-hugging carpets and are at most only a few cells thick Some mosses have conducting tissues in the center of their “stems” and may grow vertically

Bryophyte Sporophytes Grow out of archegonia Are the smallest and simplest of all extant plant groups Consist of a foot, a seta, and a sporangium Hornwort and moss sporophytes have stomata

Marchantia polymorpha, a “thalloid” liverwort LE 29-9a Gametophore of female gametophyte 500 µm Foot Seta Sporangium Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM)

LE 29-9b Plagiochila deltoidea, a “leafy” liverwort

LE 29-9c An Anthroceros hornwort species Sporophyte Gametophyte

LE 29-9d Polytrichum commune, hairy cap moss Sporophyte Gametophyte

2. Seedless Vascular Plants Pteridoyphytes: (Ferns, Club Mosses, Horsetails) DOMINANT SPOROPHYTE (grows from the gametophyte) Mature sporophyte independent FLAGELLATED SPERM (need water to swim) Animation: Fern Life Cycle

LE 29-12 Key Haploid (n) Diploid (2n) Antheridium Spore Young gametophyte Antheridium MEIOSIS Sporangium Sperm Archegonium Egg New sporophyte Sporangium Mature sporophyte Zygote FERTILIZATION Sorus Gametophyte Fiddlehead

3. VASCULAR PLANTS (naked seed and covered seed) Vascular plants have two types of vascular tissue: xylem and phloem Xylem conducts most of the water and minerals and includes dead cells called tracheids Phloem consists of living cells and distributes sugars, amino acids, and other organic products Roots anchor vascular plants absorb water and nutrients from the soil

VASCULAR STRUCTURES continued Leaves : increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

Leaves are categorized by two types: Microphylls, leaves with a single vein Megaphylls, leaves with a highly branched vascular system According to one model of evolution, microphylls evolved first, as outgrowths of stems

LE 29-13 Vascular tissue Microphylls Megaphylls

Sporophylls and Spore Variations Sporophylls are modified leaves with sporangia Homospory (Homosporous) Most seedless vascular plants One type of spore that forms a bisexual gametophyte Heterospory (Heterosporous) All seed plants and some seedless vascular 2 Types of spores (one male/ one female)

Classification of Seedless Vascular Plants There are two phyla of seedless vascular plants: Lycophyta includes club mosses, spike mosses, and quillworts Pterophyta includes ferns, horsetails, and whisk ferns and their relatives

LE 29-14a Selaginella apoda, a spike moss

LE 29-14b Isoetes gunnii, a quillwort

Diphasiastrum tristachyum, a club moss LE 29-14c Strobili (clusters of sporophyllis) Diphasiastrum tristachyum, a club moss

LE 29-14d Psilotum nudum, a whisk fern

Equisetum arvense, field horsetail Vegetative stem Strobilus on LE 29-14e Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem

Athyrium filix-femina, lady fern LE 29-14f Athyrium filix-femina, lady fern