Introduction to the Plant Kingdom: Bryophytes Chapter 20

Outline Introduction Introduction to the Bryophytes Phylum Hepaticophyta – Liverworts Phylum Anthocerophyta – Hornworts Phylum Bryophyta – Mosses Human and Ecological Relevance of Bryophytes

Introduction Plants and green algae share: Chlorophylls a and b, carotenoids Starch as food reserve Cellulose in cell walls Phragmoplast and cell plate during cell division Shared features suggest common ancestor Land plants first appeared 400 mya Ancestor progressed from aquatic to land habitat even earlier

Introduction Features preventing dessication: Plant surfaces developed fatty cuticle to retard H2O loss Gametangia (gamete-producing structures) and sporangia (spore-producing structures) became multicellular and surrounded by jacket of sterile cells Zygotes developed into multicellular embryos within parental tissues originally surrounding egg

Introduction to the Bryophytes Ca. 23,000 species of bryophytes Include mosses, liverworts, and hornworts Occupy wide range of habitats: Damp banks, trees, logs Bare rocks in scorching sun Frozen alpine slopes In elevations from sea level up to 5,500 m or more

Introduction to the Bryophytes Bryophytes often have mycorrhizal fungi associated with rhizoids Peat mosses ecologically important in bogs Luminous mosses found in caves and other dark, damp places None have true xylem or phloem Many have hydroids for H2O conduction Most H2O absorbed directly through surface Few have leptoids for food-conduction Need H2O to reproduce sexually

Introduction to the Bryophytes Exhibit alteration of generations In mosses, leafy plant = gametophyte generation Sporophyte generation grows from gametophyte 3 distinct bryophyte phyla None appear closely related to other living plants Bryophyte lines may have arisen independently from ancestral green algae

Phylum Hepaticophyta – Liverworts Structure and form: Most common and widespread liverworts have flattened, lobed thalli (singular: thallus) Thalloid liverworts constitute ca. 20% of spp. Other 80% leafy Thalli or leafy gametophytes develops from spores When spores germinate they may produce protonema - immature gametophyte consisting of short filaments Thalloid liverworts growth prostrate and one-celled rhizoids on lower surface anchor plant

Phylum Hepaticophyta – Liverworts Thalloid liverworts Best known species in genus Marchantia Thallus forks dichotomously as it grows Each branch apical notch and central groove Meristematic cells in notch continue to divide Bottom layer of thallus - epidermis from which rhizoids and scales arise

Phylum Hepaticophyta – Liverworts Marchantia Upper surface divided into diamond-shaped segments marking limits of chambers below Each segment has small bordered pore opening into chamber Short, erect rows of cells with chloroplasts sit on floor of chambers

Phylum Hepaticophyta – Liverworts Thalloid liverworts Marchantia - asexual reproduction: Gemmae (singular: gemma) - tiny, lens-shaped pieces of tissue become detached from thallus Produced in gemmae cups scattered over upper surface of thallus

Phylum Hepaticophyta – Liverworts Thalloid liverworts Marchantia - sexual reproduction: Gametangia formed on gametophores Male gametophore = antheridiophore Antheridia containing flagellated sperm found on upper surface

Phylum Hepaticophyta – Liverworts Marchantia - sexual reproduction cont’d.: Female gametophore = archegoniophore Archegonia with eggs in rows and hang down beneath spokes of archegoniophore

Phylum Hepaticophyta – Liverworts Marchantia - sexual reproduction cont’d.: Embryo dependent on gametophyte for sustenance Foot of sporophyte anchors to archegoniophore Seta - short stalk Capsule - meiosis produces 1n spores inside Also contains 2n elaters with spiral thickenings Immature sporophyte protected by calyptra = caplike tissue that grows out from gametophyte

Phylum Hepaticophyta – Liverworts Marchantia - sexual reproduction cont’d.:

Phylum Hepaticophyta – Liverworts Leafy liverworts 2 rows of partially overlapping leaves No midrib Often have folds or lobes Cells contain oil bodies 3rd row of underleaves often present Archegonia and antheridia produced in cuplike structures composed of modified leaves, in axils of leaves or on separate branches Sporophyte pushes out from among leaves

Phylum Anthocerophyta – Hornworts Structure and form: Mature sporophytes look like miniature greenish-blackish rods Gametophytes thalloid Cells with only 1 large chloroplast Thalli have pores and cavities filled with mucilage often containing N2-fixing bacteria Ca. 100 spp. worldwide Asexual reproduction by fragmentation of thallus

Phylum Anthocerophyta – Hornworts Sexual reproduction: Archegonia and antheridia produced in rows just beneath upper surfaces of gametophytes Sporophyte: Numerous stomata Meristem above foot continually increases length of sporophyte from base Meiosis produces 1n spores 2n elaters also produced

Phylum Bryophyta – Mosses Structure, form and classes: Ca. 15,000 spp. of mosses Divided into 3 classes: Peat mosses True mosses Rock mosses A true moss

Phylum Bryophyta – Mosses Structure, form and classes cont’d.: Leaves of moss gametophytes have blades nearly always one-cell thick, except at midrib, and never lobed or divided Cells usually contain numerous chloroplasts Peat moss leaves have large transparent cells without chloroplasts that absorb H2O; and small, green, photosynthetic cells sandwiched between Axis stemlike, without xylem or phloem Often with hydroids Cells of peat moss leaves

Phylum Bryophyta – Mosses Sexual reproduction: Gametangia at apices of leafy shoots Archegonium cylindrical with egg in swollen base, and neck above containing narrow canal Multicellular filaments = paraphyses scattered among archegonia

Phylum Bryophyta – Mosses Sexual reproduction cont’d.: Antheridia on short stalks, surrounded by walls 1 cell thick Sperm cells, each with pair of flagella, formed inside Sperm forced out top of antheridium Paraphyses scattered among antheridia

Phylum Bryophyta – Mosses Sexual reproduction cont’d.: Archegonia release substances attracting sperm Sperm swim down neck of archegonium Zygote grows into spindle-shaped embryo Top of archegonium splits off and forms cap on top of sporophyte = calyptra Mature sporophyte consists of capsule, seta and foot

Phylum Bryophyta – Mosses Sexual reproduction cont’d.: Meiosis produces spores inside capsule Peristome, composed of 1 or 2 rows of teeth, under operculum at tip of capsule Peristome opens or closes in response to humidity Spores develop into filamentous protonema that produces buds developing into leafy gametophytes

Phylum Bryophyta – Mosses Sexual reproduction cont’d.:

Human and Ecological Relevance of Bryophytes Pioneer species on bare rock after volcanic eruptions or other geological upheavals = succession Accumulate mineral and organic matter utilized by other organisms Retain moisture, and reduce flooding and erosion Indicators of surface H2O

Human and Ecological Relevance of Bryophytes Peat mosses most important bryophyte to humans Soil conditioner due to high absorptive capacity Poultice material due to antiseptic properties and absorbency Fuel

Review Introduction Introduction to the Bryophytes Phylum Hepaticophyta – Liverworts Phylum Anthocerophyta – Hornworts Phylum Bryophyta – Mosses Human and Ecological Relevance of Bryophytes