Biology 1010 Chapter 20 Bryophytes

Bryophytes What are they?? Where are they found?? What is their evolutionary & ecological importance??

Points to Ponder Differentiate the bryophyte phyla from each other and other phyla Describe the bryophyte adaptations to terrestrial environments Describe reproduction in bryophyte phyla Describe the ecological role of bryophytes

Kingdom Plantae Bryophytes: simplest plants Include liverworts, hornworts, mosses Fossils from 400 mya Molecular evidence suggests 700 mya Economically important species Sphagnum moss from peatlands Cool northern areas: Canada, n. US, Ireland Modifies soil to retain H2O, adds organic material Fuel source Acid pH or antibiotic compounds: aid wound healing

Bryophyte Overview Life on land possible when Oxygen level > 2 % Present oxygen level?? Water can be retained Bryophytes found in moist environments Term refers to nonvascular plants Formerly one phylum Now: three phyla Each evolved independently From the same green algal ancestors

Phylum Hepatophyta Liverworts 1st land plant fossil 450 mya 6000 spp 1st land plant fossil 450 mya Probably liverwort Advantages of land: Intense sunlight Rocks rich in minerals

Phylum Anthocerophta Possible path of evolution: 100 spp Hornworts Possible path of evolution: Stranding of green algae with prior adaptations Adaptations include: vertical stems underground stems for H2O & nutrient uptake

Phylum Bryophyta 9,600 spp Bryophytes limited to moist environments Mosses Bryophytes limited to moist environments Sperm requires water Just as amphibians do Some can live in dry sites Do not fossilize well Molecular evidence 700 mya

Bryophyte characteristics Nonvascular: no xylem & phloem Restricts size, limits distribution on land Gametophytes have structures Resemble stems & leaves Without internal ‘veins’ Hydroids: conduct H2O Leptoids: conduct food Thallus: body of a bryophyte Rhizoid: anchors bryophyte to substrate Absorption occurs through contact

Bryophytes similar to Charophyceae & vascular plants Classification of algae & plants unsettled Should reveal phylogeny Similarities between charophyceae & plants Cellulose in cell walls Mitotic spindles remain during cytokinesis Pigments: Phytochrome, Chla, b, carotenoids, Thylakoids stacked in grana

Bryophytes similarity to plants Characteristics that enhance survival on land Protect gametes and spores Sterile cells protect structures producing male and female gametes multicellular embryo protected within female parent Multicellular, diploid sporophyte meiosis → spores Sterile cells protect multicellular sporangia Natural selection guided bryophyte evolution from green algae differently than plants

Bryophyte Alternation of Generations Gametophyte dominant Haploid Gametangia: mitosis → gametes Antheridia: male Archegonia: female, one egg Sporophyte attached to gametophyte Depends on gametophyte for its nutrition Diploid Meiosis → haploid spores in sporangium Spore germinates → protonema

Bryophyte Asexual Reproduction All 3 phyla can reproduce by fragmentation Reproduce through specialized brood bodies Gemmae bulbils

Ecological roles of Bryophytes Plant succession Mosses colonize rock surfaces, crevices → soil Rhizoids secrete acid to dissolve rock Bodies add organic matter, collect dust Seeds germinate in these pockets Epiphytic mosses: Grow in tropical and temperate rain forest trees Important in tundra NOT “reindeer moss” = lichen

Bryophytes tolerate drought Liverworts may roll into tube Protects upper surface Tortula spp Moss can dehydrate Produce mRNA Codes for protein to repair damage Rehydration → resumption of photosynthesis

P. Hepatophyta = liverworts Earliest land plants? Closely related to green algae Lack DNA characteristic of other bryophytes, plants Horizontal, flatter than mosses Leaves usually thin, flat Categories: Thalloid or leafy

Liverwort life cycle Gametophyte dominant Marchantia Lobed gametophyte large Rhizoids penetrate soil Antheridia & archegonia elevated Antheridiophore flattened, bears antheridia, catch rain drops Archegoniophore suspends archegonia beneath tops Sporophyte inconspicuous Zygote in archegonium Forms spores

P. Anthocerophyta = hornworts Conspicuous horn-shaped sporophytes Stomata with guard cells: new feature Gametophytes similar to liverworts Rumpled, green sheet N-fixing bacteria symbionts

Hornwort life cycle Gametophyte form antheridia Become visible when sterile cells dry & break Archegonia form from surface cells Thallus cells surround egg Fertilization → zygote with ‘horn’ Sporophyte foot anchors it to gametophyte Gametophyte provides water, minerals, some food Sporophyte grows from its base not its apex photosynthetic as in liverworts, NOT mosses Produces spores from apex of sporangium to base

P. Bryophyta = mosses bryophytes refers to ALL nonvascular plants P. Bryophyta = scientific classification Mosses usually with a leafy thallus Vertical gametophyte Usually in moist, forested sites, wetlands Sometimes in deserts, dry rock outcrops Some aquatic

Class Spagnopsida aka Sphagnidae 150 spp, peat mosses Sheet like protonema Dead cells with thick walls hold water spherical sporangia attach to stalks of gametophytes

Class Andreaeopsida = granite or rock mosses 100 spp Live at high altitudes Cold, temperate sites Live on rock, snow, ice Sporangia with four slits allow dispersal of spores

Class Bryopsida aka Bryidae 9,000 spp Common mosses Growth patterns vary May grow in clumps As pendulous epiphytes May remain filamentous May be seasonal May grow on polluted soil

Life cycle of Polytrichum Typical moss life cycle Dominant gametophyte Survives drought Originates from spore Spore → protonema Bud → gametophyte leaf → Antheridia &/or archegonia Water → fertilization Zygote develops in archegonium → sporophyte with setae foot absorbs food

Questions Thought and Discussion 2 4 Evolution Connection