VI. Division Pterophyta (Ferns)

A. General information

1. Historically, ferns have been used as food and medicine and were often an ingre-

dient in folk remedies

2. Today ferns are commonly used as houseplants and ornamental plants

3. In natural ecosystems, they are an important food source for wildlife

B. Structure

1. Ferns vary in size from small floating forms less than 1 cm in diameter to large,

tropical, treelike ferns up to 25 meters tall

2. These plants possess large, highly divided, feathery leaves called fronds

a. Fronds first appear as small, tightly coiled structures called fiddleheads,

which uncurl to form mature fronds

b. There are two types of fronds

1. Vegetative fronds are involved only in photosynthesis

2. Reproductive fronds have sporangia for the production of spores

C. Reproduction

1. Spore production begins in the sporangia, which are often found in clusters

(called sori) on the underside of fronds (see Life Cycle of the Fern, page 94)

a. In many ferns, the sori are protected by flaps of covering tissue called an in-

dusium; as the sporangia mature, the indusium shrivels to expose the spo­rangia beneath it

b. Each sporangium has a conspicuous row of thick-walled cells along one

edge, which are known as the annulus

c. The annulus catapults spores out of the sporangium using a snapping action

that is influenced by moisture changes within the cells

d. The individual sporangia contain diploid cells (parental cells) that undergo

meiosis to produce haploid spores

2. Released spores germinate and form a heart-shaped prothallus

3. The prothallus is a multicellular, independent, photosynthetic gametophyte

4. Archegonia develop on the under surface of the prothallus near a notch in the

heart shape; antheridia develop near the apex

5. After fertilization, the zygote formed in the archegonium continues to grow into an

independent sporophyte, which is the recognizable fern

Seed Vascular Plants: Gymnosperms

Objectives

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

• Define gymnosperm.

• Differentiate between gymnosperms and angiosperms.

• List and describe the major divisions of gymnosperms.

• Describe the life cycle of a pine tree.

• Discuss the human and ecologic importance of gymnosperms.

I. Seed Vascular Plants

A. General information

1. Seed plants are so named because the seed is the chief reproductive propagule

a. A seed consists of an embryo that is packaged with stored food and sur-

rounded by a protective seed coat; the stored food is used for energy dur­ing germination and early seedling development

b. The seed permits the plant to survive harsh environmental conditions (cold

or lack of moisture) during a period of seed dormancy

2. All seed vascular plants have conducting tissue consisting of xylem and phloem

3. All seed-bearing plants exhibit alternation of generations

a. The gametophyte generation in these plants is extremely small and develops

within the tissues of the sporophyte

1. The male gametophyte is the pollen grain

2. The female gametophyte is the embryo sac

b. All seed plants are heterosporous (produce two kinds of spores); the mega-

spore gives rise to the female gametophyte and the microspore gives rise to the male gametophyte

c. Seed plants generally do not require water for fertilization because, in most

varieties, the sperm are not flagellated and do not swim to the archegonia

B.Taxonomic classification

1. Seed plants are classified as gymnosperms or angiosperms

a. Gymnosperms produce seeds in structures open to the environment

b. Angiosperms (flowering plants) produce seeds in specialized reproductive

structures called flowers

c. Gymnosperms are primarily trees and shrubs; angiosperms encompass a di-

verse variety of life forms

2. The four divisions of gymnosperms are Coniferophyta, Cycadophyta, Ginkgo-phyta, and Gnetophyta