IV. Importance

A. General information

1. Naturally occurring fungi are important in the decomposition of dead organisms

and also can cause disease

2. Cultivated fungi are used as food and as sources of antibiotics and other valuable

substances

B. Edible varieties

1. Edible fungi include truffles and morels (sac fungi), Agaricus bisporus or culti-

vated mushrooms (club fungi), and shiitake mushrooms from China and Japan (also club fungi)

2. The sac fungus yeast (Saccharomyces cerevisiae) is used in baking and fermen-

tation processes

C. Decomposer varieties

1. In nature, fungi serve as decomposers, breaking down dead plant and animal

matter into their component organic materials

2. As decomposers, fungi play an important role in sustaining ecosystems

a. They permit recycling of nutrients bound up in the tissues of organisms

b. These nutrients would otherwise be unavailable to sustain new growth

D. Intoxicating, poisonous, and hallucinogenic varieties

1. The Conocybe and Psilocybe mushrooms have intoxicating and hallucinogenic

properties; they were used by the ancient Mayans for religious ceremonies and are still used by the native peoples of Mexico and Central America

2. Amanita phalloides and Amanita verna (collectively known as the destroying an-

gel, death angel, or death cup) are extremely poisonous; both species appear similar to edible varieties, but can be lethal even if ingested in small quantities

Kingdom Plantae: Nonvascular Plants

Objectives

After studying this chapter, the reader should be able to:

• Describe the most important characteristics of members of the Plant kingdom.

• Explain the concept of alternation of generations.

• Describe the ecologic importance of bryophytes.

• Describe the life cycles of liverworts, hornworts, and mosses.

I. Introduction to the Plant Kingdom

A. General information

1. All member of the plant kingdom are multicellular organisms composed of eu-

karyotic cells

2. All plants contain chlorophylls a and b, and many possess carotenoid as well

3. Plant cells use starch as the storage carbohydrate and cellulose as the structural

polysaccharide in cell walls

4. Plant reproduction is primarily sexual, although asexual reproduction occurs

5. Evolutionary trends in the Plant kingdom are related to the modifications or adap-

tations necessary for living in terrestrial environments; for example, because dehydration is a possibility in such environments, plants have developed meth­ods of controlling water loss

B. Alternation of generations

1. Alternation of generations is the typical sexual life cycle of a plant in which a

sporophyte generation alternates with a gametophyte generation

2. The sporophyte generation is the spore-producing diploid generation of the life

cycle

a. Spores are produced by meiosis within the sporophyte

b. These spores undergo cell division to form a multicellular gametophyte

3. The gametophyte generation is the gamete-forming haploid generation of the

life cycle

a. The gametes (egg and sperm) are produced by mitosis and contained within

a sterile jacket of cells to prevent desiccation (drying out)

b. The haploid gametes unite through fertilization to produce a diploid zygote,

or sporophyte

4. Plant divisions vary as to which generation (sporophyte or gametophyte) predomi-

nates

(I. Nonvascular Plants (Bryophytes)

A. General information

1. Nonvascular plants lack the vascular and transport tissue (xylem and phloem)

found in other plants

2. These plants are members of the division Bryophyta and are found in cool,

shaded, extremely moist areas; however, many bryophytes can withstand long periods of desiccation

3. Bryophytes are ecologically important in forming bogs (peat moss) and in devel-

oping ecologic communities, a process known as succession

4. Many bryophytes have associated mycorrhizal fungi

5. They have flagellated, swimming sperm and require water for successful fertiliza-

tion

6. They spend most of the life cycle as gametophytes; the sporophyte remains at-

tached to and lives off the gametophyte

7. The three classes of bryophytes are liverworts, hornworts, and mosses

B. Class Hepaticae (liverworts)

1. Liverworts consist of a thin, flattened structure called a thallus

a. The thallus develops directly from a spore

b. Its smooth upper surface has various markings and pores; the underside

bears many tiny, single-cell, roothke structures known as rhizoids, which anchor the thallus to the substrate

2. Representative liverworts are Marchantia (common liverwort) and Porella (leafy

liverwort)

3. The life cycle of the liverwort is typified by Marchantia

a. Asexual reproduction occurs by fragmentation and the production of gem-

mae, clusters of lens-shaped cells that detach from the parent

(1) Gemmae are produced in specialized cuplike structures formed on the

upper surface of the thallus

(2) The gemmae are dispersed by rainfall, and each gemma is capable of

growing into a new thallus

b. Sexual reproduction begins with the gametophyte generation

(1) The male and female thalli of the gametophyte generation produce

male and female gametangia

(2) The gametangia are upright, umbrella-like structures that extend above

the thallus and produce gametes within specialized structures known as antheridia and archegonia

(a) The numerous antheridia within the upper surface of the male

gametangium produce many sperm

(b) The archegonia on the under surface of the female gametangium

contains a single egg

(3) When the flagellated sperm are released during a rainstorm, they swim

to the archegonia to fertilize the egg

(4) Fertilization produces a zygote that develops into an embryo (imma-

ture sporophyte)

(5) The embryo remains attached to the archegonium as it grows into a

mature sporophyte, which consists of three parts: foot (point of attach­ment to archegonium); seta (short thick stalk); and capsule or sporan­gium (structure in which meiosis occurs to form haploid spores)

(6) At maturity, the spores are released from the capsule and form a new thallus when they reach a suitable habitat

C. Class Anthocerotae (hornworts)

1. Hornworts resemble liverworts, but during the sporophyte generation, they form

hornlike structures that give the class its name

2. The hornwort thalli often produce a mucilage secretion in which nitrogen-fixing

cyanobacteria grow

a. This relationship provides the hornwort with a source of nitrogen

b. The presence of cyanobacteria may also provide some coloration

D. Class Musci (mosses)

1. Mosses consist of leaflike structures that contain photosynthetic material but lack

a midrib with vascular tissue and therefore are not considered true leaves

2. These low-growing green plants typically are found in moist, shady habitats

3. Asexual reproduction occurs by fragmentation

4. Sexual reproduction begins with the germination of a haploid spore (see Life Cy-

cle of Moss, page 89)

a. The spore forms an algae-like, green filamentous structure called a pro-

tonema

b. The protonema eventually grows to become a leafy gametophyte, which pro-

duces male and female gametangia in its sperm-producing antheridia and egg-producing archegonia

c. The zygote that results from fertilization develops into an embryo while still

within the archegonium

d. The embryo grows to form a sporophyte

e. Haploid spores produced by meiosis within the sporophyte capsule are re-

leased when the operculum (cap) falls off

f. They are dispersed by wind and eventually germinate to complete the life

cycle

E. Importance

1. Bryophytes may have been the first plants to grow on barren or bare surfaces

2. They are a chief source of food in the arctic circle, where they are eaten by rein-

deer, caribou, and other animals

3. Mosses retain moisture and can potentially reduce flooding and erosion in natu-

ral ecosystems

4. They also contribute to the humus content of soil; for example, peat moss is used

as a soil conditioner to promote moisture retention and increase the nutrient status of soils

Nonseed Vascular Plants: Ferns and Their