Introduction to the Plant Kingdom: Bryophytes

Outline Introduction Phylum Hepaticophyta - Liverworts Leafy Liverworts Phylum Anthocerophyta - Hornworts Phylum Bryophyta - Mosses

1. Mostly sexual reproduction although asexual forms occur Features of the Plant Kingdom A. General Characteristics 1. Major pigments (chlorophylls a and b) 2. Starch as reserve food product 3. Cellulose in cell walls 4. Phragmoplasts and cell plate 5. Fatty cuticle 6. Stomates B. Reproduction 1. Mostly sexual reproduction although asexual forms occur 2. Gametangia protected from desiccation 3. Embryos formed 4. Distinct alternation of generations

Introduction to the Bryophytes About 23,000 species of bryophytes. Include mosses, liverworts, and hornworts. Habitats range in elevation from sea level up to 5,500 meters or more. Small, low-to-the-ground plants, moist shaded habitats. Bryophytes of all phyla often have mycorrhizal fungi associated with their rhizoids. In some instances, fungi apparently are at least partially parasitic.

Introduction to the Bryophytes Peat mosses are ecologically important in bogs. Luminous mosses are found in caves and in other dark, damp places. None have true xylem or phloem. Many have hydroids (xylem-like) and leptoids (phloem-like). Exhibit alternation of generations. - Gametophyte, the green leafy generation. - Sporophyte produces spores, grows from tip of leafy gametophyte.

Phylum Hepaticophyta - Liverworts Structure and Form Most common liverworts have flattened, lobed thalli. Gametophyte stage develops from spores. When spores germinate they may produce immature gametophyte (protonema).

Phylum Hepaticophyta Thalloid Liverworts Best known species are in the genus Marchantia. Thick thallus that forks dichotomously as it grows. Consists of parenchyma cells with few, if any, chloroplasts.

Fig. 20.4

Section of Marchantia Thallus

Reproduction in Marchantia Sexual a. Male and female gametophores produce antheridia and archegonia b. Flagellated sperm fertilize egg in archegonium c. Embryo (immature sporophyte) develops d. Sporophyte consists of foot, seta, and capsule e. Meiosis takes place in the capsule f. Capsule decays and spores aided in their release by spiral shaped elaters Asexual gemmae cups separate from parent thallus

Marchantia Sporophyte

Asexual Reproduction of Marchantia

Leafy Liverworts Always have two rows of partially overlapping “leaves” whose cells contain distinctive oil bodies. Often have folds and lobes. Archegonia and antheridia are produced in cup-like structure. At maturity, sporophyte capsule may be pushed out as the seta elongates. Germinating spore produces a protonema.

Fig. 20.8

Phylum Anthocerophyta Hornworts Structure and Form Mature sporophytes look like miniature greenish-blackish rods. Only about 100 species worldwide. Thalli have pores and cavities filled with mucilage, that often contain nitrogen-fixing bacteria.

Fig. 20.9a

Hornworts Asexual Reproduction Fragmentation Separation of lobes from main thallus. Sexual Reproduction Archegonia and antheridia are produced in rows beneath the upper surface of the gametophytes. Have both unisexual and bisexual plants. Sporophyte develops from zygote, has numerous stomata. Meiosis takes place in sporophyte “horn” Spores released when sporophyte tip splits open in longitudinal segments.

Hornwort Sporophyte

Phylum Bryophyta Mosses Structure, Form, and Classes About 15,000 species of mosses currently known. Divided into three classes: Peat Mosses True Mosses Rock Mosses

Fig. 20.10

Mosses “Leaves” of moss gametophytes have no mesophyll tissue, stomata, or veins. Blades are nearly always one-cell thick, and are never lobed or divided. Initially formed in three ranks and usually end up appearing to be arranged in a spiral or alternately on an axis that twists as it grows.

Sexual Reproduction in Mosses 1. Female gametangium are called the archegonium (flask shaped) 2. Male gametangium are called the antheridium (club shaped) 3. Gametangia produced at tips of leafy gametophytes 4. Sperm are flagellated and reach archegonium by swimming in a film of water 5. Sporophyte develops in base of archegonium and grows into a foot, seta, and a capsule 6. Calyptra sits on top of capsule 7. Meiosis takes place in the capsule producing spores 8. Peristome teeth at rim of capsule aid in dispersal of spores 9. Spores germinate on moist soil and develop into an algal-like protonema 10. Protonema develops tiny "leafy" buds which will produce the upright gametophytes

Asexual Reproduction in Mosses Fragments of leaves, stems, and rhizoids can develop protonema.

Phylum Bryophyta Human and Ecological Relevance Pioneer Species of Primary Succession. Rapidly colonize bare or burned soil. Indicators of Surface Water Packing Material Peat Mosses Soil Conditioner: retention of water in dead, empty cells (1 kilogram of dry peat moss will take up 25 kilograms of water) Antiseptic (antibiotic) properties: The natural acidity produced inhibits bacterial and fungal growth and gives. Because of its water absorbing ability and antispetic characteristics, peat moss was used in dressing wounds (poultice material) in World War I. Fuel - Peat deposits harvested and burned in stoves. - Peat smoke used to flavor Scotch whisky.

Review Introduction Phylum Hepaticophyta - Liverworts Leafy Liverworts Phylum Anthocerophyta - Hornworts Phylum Bryophyta - Mosses

Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display