Introduction to Seed Plants: Gymnosperms

Outline

• Overview• Phylum Pinophyta• Phylum Ginkgophyta• Phylum Cycadophyta• Phylum Gnetophyta• Human Relevance of Gymnosperms

Conifers Other Gymnosperms

Overview

• Gymnosperm refers to the exposed nature of the seeds. Produced on the surface of sporophylls or

similar structures instead of being enclosed within a fruit as in flowering plants.

- Female gametophyte is produced inside an ovule that contains a nucellus.

Enclosed in integument. Four living Phyla

The Plant Ovule

Exposed versus Enclosed Seeds

Phylum Pinophyta

• The Conifers Pines

- Largest genus of conifers. Over 100 living species.

Include world’s oldest known living organisms (Bristlecone Pines).

Phylum Pinophyta

• Structure and Function Pine leaves are needlelike and are

arranged in clusters of bundles of two to five leaves.

- Each cluster (fascicle) forms a cylindrical rod if the leaves are held together.

Hypodermis located below the epidermis. Resin canals develop in mesophyll.

- Antiseptic and Insect Deterrent.

Pine Stem Cross Section

Phylum Pinophyta

• Most wood varies considerably in hardness. Most gymnosperm wood consists primarily

of tracheids.- No vessel members or fibers.

Soft Wood Mycorrhizal fungi associated with the roots

of most conifers.

Fig. 22.8

Pine Life Cycle

Pine Life Cycle

Pine Ovule - Longitudinal Section

Fig. 22.9

Fig. 22.10

Phylum Ginkgophyta

• Ginkgo (Maidenhair Trees) Only one living species.

- Notched, broad, fan-shaped leaves. Leaves are produced in a spiral on

short, slow-growing spurs. No midrib or prominent veins.

Hair-like veins branch dichotomously.- Life cycle similar to pines.

Dioecious

Fig. 22.11

Phylum Cycadophyta

• The Cycads- Appearance of a cross between a tree

fern and a palm. Slow-growing plants of the tropics that

have tall unbranched trunks. Crown of largely pinnately divided

leaves.- Life Cycle similar to conifers.

Pollination is generally brought about by beetles instead of wind.

Fig. 22.12

Phylum Gnetophyta

• The Gnetophytes Unique among the gymnosperms in having

vessels in the xylem. More than half of the 70 known species are

joint firs in the genus Ephedra. Most of remaining species are in genus Gnetum.

- Occur in tropics- Most are vine-like with broad leaves

similar to those of flowering plants.

Fig. 22.13

Fig. 22.14

Phylum Gnetophyta

Third genus, Welwitschia, has only one species.

- Confined to temperate deserts of southwestern Africa.

Average rainfall only 2.5 cm. Plant use CAM photosynthesis.

- Only produce two leaves throughout their life span.

Fig. 22.15

Human Relevance of Gymnosperms

• Conifers Edible Seeds Crates, Boxes, Matchsticks, Furniture Telephone Poles Turpentine and Rosin (Resin) Fuel (Pitch) Pulpwood Ornamentals Pharmaceuticals (Taxol)

Human Relevance of Gymnosperms

• Other Gymnosperms Ginko Seeds - Food Ephedra - Mormon tea

Review

• Overview• Phylum Pinophyta• Phylum Ginkgophyta• Phylum Cycadophyta• Phylum Gnetophyta• Human Relevance of Gymnosperms

Conifers Other Gymnosperms

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