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