Plant Diversity I How Plants Colonized Land

Closest relatives??? Green algae called charophyceans are the closest relatives of land plants Green algae called charophyceans are the closest relatives of land plants

Why do we think this? Land plants share only with charophyceans: Land plants share four key traits only with charophyceans: Rose-shaped complexes for cellulose synthesis Rose-shaped complexes for cellulose synthesis Peroxisome enzymes Peroxisome enzymes Structure of flagellated sperm Structure of flagellated sperm Formation of a phragmoplast Formation of a phragmoplast NOTE: In charophyceans a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out NOTE: In charophyceans a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out

LE 29-4 Viridiplantae Streptophyta Plantae Red algae Chlorophytes Charophyceans Embryophytes Ancestral alga

Derived Traits of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans: Apical meristems Apical meristems Alternation of generations Alternation of generations Walled spores produced in sporangia (sporocytes – mother cells--go through meiosis to generate spores Walled spores produced in sporangia (sporocytes – mother cells--go through meiosis to generate spores Multicellular gametangia (archegonia and antheridia) Multicellular gametangia (archegonia and antheridia) Multicellular dependent embryos—some land plants called embryophytes Multicellular dependent embryos—some land plants called embryophytes

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

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

How do we group land plants They can be grouped informally based on presence of VASCULAR TISSUE Bryophytes and Vascular plants

LE 29-7 Ancestral green alga Origin of land plants (about 475 mya) Origin of vascular plants (about 420 mya) Origin of seed plants (about 360 mya) Land plants Vascular plants Seed plants Seedless vascular plantsBryophytes Liverworts HornwortsMosses Lycophytes Pterophytes Gymno- sperms Angio- sperms Charophyceans

Grouping non-vascular plants Bryophytes: 3 phyla (informal names given) Bryophytes: 3 phyla (informal names given) Liverworts, phylum Hepatophyta Liverworts, phylum Hepatophyta Hornworts, phylum Anthocerophyta Hornworts, phylum Anthocerophyta Mosses, phylum Bryophyta Mosses, phylum Bryophyta

Which generation is dominant? In all three bryophyte phyla, In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time Sporophytes are typically present only part of the time

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

More about Bryophyte gametophytes (dominant stage) Bryophyte gametophytes Bryophyte gametophytes Produce flagellated sperm in antheridia Produce flagellated sperm in antheridia Produce ova in archegonia Produce ova in archegonia Generally form ground-hugging carpets and are at most only a few cells thick Generally form ground-hugging carpets and are at most only a few cells thick

Bryophyte sporophytes Bryophyte sporophytes Bryophyte sporophytes Grow out of archegonia Grow out of archegonia Consist of a foot, a seta, and a sporangium Consist of a foot, a seta, and a sporangium

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

LE 29-9c An Anthroceros hornwort species Sporophyte Gametophyte

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

Ecological and Economic Importance of Mosses Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Sphagnum plays an important role in the Earth’s carbon cycle Sphagnum plays an important role in the Earth’s carbon cycle

NOW…Vascular Plants (but they are seedless) There are two phyla of seedless vascular plants: There are two phyla of seedless vascular plants: Lycophyta includes club mosses, spike mosses, and quillworts Lycophyta includes club mosses, spike mosses, and quillworts Pterophyta includes ferns, horsetails, and whisk ferns and their relatives Pterophyta includes ferns, horsetails, and whisk ferns and their relatives

How are they different than Bryophytes? Sporophyte is the dominant generation Sporophyte is the dominant generation The gametophytes are tiny plants that grow on or below the soil surface The gametophytes are tiny plants that grow on or below the soil surface

LE 29-UN583 Charophyceans Bryophytes (nonvascular plant) Seedless vascular plants Gymnosperms Angiosperms

Vascular plants have two types of vascular tissue: xylem and phloem 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 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 Phloem consists of living cells and distributes sugars, amino acids, and other organic products

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

They have leaves… Increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis Increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

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

LE Vascular tissue Microphylls Megaphylls