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 O 2 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 = CO 2 and light  Soil = minerals and H 2 0 Bright sunlight unfiltered by water or plankton Plenty of CO 2, 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 Lycophytes Bryophytes 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!