Plant Diversity II: The Evolution of Seed Plants

Flashcards covering the evolution of seed plants, plant phylogenies, gymnosperms, angiosperms, and threats to plant diversity.

Plant Colonization

Plants colonized land about 500 million years ago, and the first forests appeared 385 million years ago.

Early Land Plant Evidence

Fossilized spores with sporopollenin-like material show evidence of a waxy cuticle to prevent dehydration.

Silurian-Devonian Explosion (416-359 mya)

Characterized by the appearance of vascular tissue, roots, and symbiotic fungi in plants.

Carboniferous Period (359-299 mya)

Buried seedless vascular plants from this period left significant coal deposits.

Diversification of Gymnosperms (299-145 mya)

Characterized by the evolution of seeds and pollen.

Diversification of Angiosperms (150 mya)

Characterized by the evolution of flowers.

Seeds

Can disperse over long distances via wind or other means, unlike embryophytes.

Seed

Plant embryo and food supply packaged together within a protective coat

Gamete Development in Gymnosperms

Male and female gametophytes develop within cones.

Gamete Development in Angiosperms

Male and female gametophytes develop within flowers.

Heterospory

Production of two distinct types of spores by different structures.

Microsporangia

Produce microspores that develop into male gametophytes.

Megasporangia

Produce megaspores that develop into female gametophytes.

Ovule

Consists of a megaspore within a megasporangium, surrounded by one or more protective coats called integuments.

Pollen Grain

Much-reduced male gametophyte that houses cells that will develop into sperm.

Evolutionary Advantages of Seeds Over Spores

Seeds are multicellular, can remain dormant, have stored food, and can be transported longer distances.

Seed Plants

Seed plants are a monophyletic group defined by the production of seeds and pollen grains.

Directed-Pollination Hypothesis

Natural selection favored structures that reward animals for carrying pollen directly from one flower to another.

Fruit

Structure derived from the ovary and encloses one or more seeds.

Sepals

Outer layer of a flower, usually green.

Calyx

The entire group of sepals.

Petals

Often colorful parts of a flower that help attract pollinators.

Stamens

Male reproductive structures of a flower.

Filament

Stalk for pollen transport in a flower.

Anther

Sac where microsporangia develop in a flower.

Carpels

Female reproductive structure of a flower.

Ovary

Protective chamber where megasporangia develop in a flower.

Stigma

Part of the carpel that traps pollen.

Micropyle

Opening to the embryo in the ovary.

Double Fertilization

Fertilization process in angiosperms involving two sperm cells, one forming a zygote and the other forming endosperm.

Monocot Characteristics

One cotyledon, parallel leaf veins, scattered vascular tissue, fibrous root system, one pollen opening, and floral organs in multiples of three.

Eudicot Characteristics

Two cotyledons, netlike leaf veins, vascular tissue in a ring, a taproot, three pollen openings, and floral organs in multiples of four or five.

Perfect (hermaphroditic) Flowers

Contain both stamens and carpels.

Imperfect Flowers

Contain either stamens or carpels, but not both.

Monoecious

Separate stamen- and carpel-producing flowers on the same individual.

Dioecious

Have either stamen- or carpel-producing flowers on different plants.

Ovaries

Angiosperms produce seeds in , while gymnosperms do not.

Ginkgophyta (Ginkgos)

Ginkgos lose their leaves in winter, are considered a 'living fossil,' and have separate male and female plants.

Cycadophyta (Cycads)

Cycads resemble palms, have compound leaves, separate male and female plants, and contain symbiotic cyanobacteria.

Cupressophyta (Redwoods, Junipers, Yews)

Cupressophyta range from small shrubs to giant redwood trees and have small leaf surface area to reduce water loss.

Pinophyta (Pines, Spruces, Firs)

Pinophyta are dominant plants at high latitudes and elevations, wind pollinated, and have separate male and female cones.

Gnetophyta (Gnetophytes)

Gnetophytes grow as vines, trees, or shrubs, are closely related to angiosperms, and display several angiosperm features.

Threats to Plant Diversity

Habitat destruction is threatening plant species worldwide.

Loss of Forests

Reduces the absorption of CO2 by photosynthesis, contributing to global warming.

Consequences of Plant Species Loss

The loss of plant species is accompanied by the loss of supporting insects and animals.