Topic 13

Introduction to the Kingdom Plantae

Biology 1001 November 2, 2005

LAND Plants & The Tree of Life

13.1 What Are Plants? Plants colonized land approximately 500 MYA Land plants are a monophyletic group! Land plants evolved from aquatic green algae 290,000 living species Producers – sources of O2 and food for land animals

Multicellular, eukaryotic photoautotrophs Cell walls containing cellulose Chloroplasts containing chlorophylls a and b

What Features DEFINE plants?

The Evolution of Land Plants Features shared with charophyceans Terrestrial adaptations that characterize land plants Origin and diversification of land plants

General Features of Land Plants

Land Plants Evolved From Green Algae Green algae called

charophyceans are the closest living relatives of land plants

Evidence Rosette cellulose-synthesizing

complexes Peroxisome enzymes that minimize

photorespiration Similarity of sperm structure Formation of a phragmoplast Similar nuclear and chloroplast

genomes Adaptation to a dry environment

=sporopollenin

Adaptations to a Terrestrial Environment

Defining the plant kingdom

Five key derived traits of plants Apical meristems Alternation of generations Walled spores produced in

sporangia Multicellular gametangia Multicellular, dependent

embryos

Land vs. Water Some combination of characteristics allowed the first

plants to survive and reproduce on land; once there the many benefits of this new environment led to the evolution of this successful and diverse group of organisms

Aerial and subterranean environments Aerial = CO2 and light Soil = minerals and H20

Bright sunlight unfiltered by water or plankton Plenty of CO2, soil rich in nutrients Initially few herbivores and pathogens

APICAL MERISTEMS

Figure 29.5a (!) Localized regions of cell

division at the tips of roots and shoots

Produce roots and leaf-bearing shoots

Structural specialization that allows plants to flourish in separate aerial and subterranean environments

ALTERNATION OF GENERATIONS

Figure 29.5b (!) Also evolved in various

groups of algae but does not occur in the charophyceans

In some groups of plants the gametophyte generation is dominant, in others the sporophyte

In flowering plants, the gametophyte generation is highly reduced

WALLED SPORES PRODUCED IN SPORANGIA Figure 29.5c (!) Spores are produced in organs called sporangia Spore walls are enriched with sporopollenin Allows them to survive the dry terrestrial environment Charophycean sporopollenin protects the zygote, and they lack sporangia

MULTICELLULAR GAMETANGIA

Figure 29.5d(!) Gametes are produced in

multicellular organs of the gametophyte called gametangia

Male = antheridia Female = archegonia The sperm fertilizes the

egg in the archegonia, and that is where the zygote develops

MULTICELLULAR, DEPENDENT EMBRYOS Figure 29.5e(!) The embryo (developing young sporophyte) is retained within

the tissues of the female parent Nutrients are transferred from parent to embryo through

placental transfer cells This is why land plants are embryophytes

Other Terrestrial Adaptations Have evolved in many but not all plant

species

An epidermal covering known as a cuticle prevents dessication

Secondary compounds such as Alkaloids, terpenes, and tannins

defend against herbivores and parasites

Flavenoids absorb harmful UV rays Phenolics prevent bacterial infections

Cuticle

Tannins

Lignin – a phenolic

Origin and Diversification of Plants Fossilized sporophyte tissue &

molecular evidence place the origin of plants at ~ 475 MYA The first plants were nonvascular

There have been three subsequent major evolutionary adaptations or adaptive radiations of plants Vascular plants evolved ~ 420

MYA Seed plants evolved ~ 360 MYA Flowering plants evolved ~ 130

MYA

Figure 29.7 (!) Highlights of Plant Evolution

Highlights of Plant Evolution

Nonvascular and all subsequent plants have the five key terrestrial features

Vascular plants have complex vascular tissue systems composed of xylem and phloem

Seed plants package their embryos with a supply of nutrients into a seed

Flowering plants develop their seeds inside a chamber called the ovary

Some Examples of Land Plants

Pterophytes and LycophytesBryophytes

Pallavicinia – a “thalloid” liverwort

Porella – a “leafy” liverwort

Phaeoceros - a hornwort

Polytrichum commune – star moss

Lycopodium – a club “moss”

Psilotum – a whisk fern

Equisetum - a horsetail

Polypodium vulgare – a fern

Some Examples of Land Plants

Gymnosperms

Some Examples of Land Plants

Angiosperms – 250,000 species!