Plant Diversity

Domain Archaea

Domain Bacteria Universal ancestor Domain Eukarya

Angiosperms

Cnidarians (jellies, coral)

Sponges

Choanoflagellates

Club fungi

Sac fungi

Chapter 31

Animals

Bilaterally symmetrical animals (annelids, arthropods, molluscs, echinoderms, vertebrates)

Fungi

Arbuscular mycorrhizal fungi

Chapter 30 Chapter 28 Zygote fungi

Chytrids

Amoebozoans (amoebas, slime molds)

Plants

Gymnosperms

Chapter 29 Seedless vascular plants (ferns)

Chapter 28

Bryophytes (mosses, liverworts, hornworts)

Charophyceans

Chlorophytes

Red algae

Cercozoans, radiolarians

Stramenopiles (water molds, diatoms, golden/brown algae)

Chapter 27

Alveolates (dinoflagellates, apicomplexans, ciliates)

Euglenozoans

Diplomonads, parabasalids

Euryarchaeotes, crenarchaeotes, nanoarchaeotes

Korarchaeotes

Gram-positive bacteria

Cyanobacteria

Spirochetes

Chlamydias

Proteobacteria

Plant Diversity Chapter 32 Chapters 33, 34

Fossilized spores and tissues – Have been extracted from 475-millionyear-old rocks Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right).

25.3

Fossilized sporophyte tissue. The spores were embedded in tissue that appears to be from plants.

Genetic Evidence • Comparisons of both nuclear and chloroplast genes point to charophyceans as the closest living relatives of land plants

(a) Chara, a pond organism

10 mm

40 µm

25.3

(b) Coleochaete orbicularis, a diskshaped charophycean (LM)

Five Traits #1 Apical meristems

#2 Alternation of generations 25.1-2

Five Traits #3 Walled spores produced in sporangia

#4 Multicellular gametangia 25.1

Five Traits

#5 - Multicellular dependent embryos 25.1

Bryophyte diversity Gametophore of female gametophyte

LIVERWORTS (PHYLUM HEPATOPHYTA)

Plagiochila deltoidea, a “leafy” liverwort

Foot Seta

Marchantia sporophyte (LM) HORNWORTS (PHYLUM ANTHOCEROPHYTA) An Anthoceros hornwort species Sporophyte

Sporangium 500 µm

Marchantia polymorpha, a “thalloid” liverwort

MOSSES (PHYLUM BRYOPHYTA) Polytrichum commune, hairy-cap moss Sporophyte

Gametophyte Gametophyte

25.4

Importance of Mosses • Sphagnum, or “peat moss” – Forms extensive deposits of partially decayed organic material known as peat – Plays an important role in the Earth’s carbon cycle (a) Peat being harvested from a peat bog

(b) Closeup of Sphagnum. Note the “leafy” gametophytes and their offspring, the sporophytes.

(c) Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality.

(d)

“Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years.

Gametophyte

Sporangium at tip of sporophyte Living

photo- Dead watersyntheticstoring cells 100 µm cells

Life Cycles with Dominant Sporophytes • In contrast with bryophytes – Sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern – The gametophytes are tiny plants that grow on or below the soil surface

25.5

The life cycle of a fern 1 Sporangia release spores. Most fern species produce a single type of spore that gives rise to a bisexual gametophyte.

Key

2 The fern spore develops into a small, photosynthetic gametophyte.

3 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanisms promote cross-fertilization between gametophytes.

Haploid (n) Diploid (2n)

Antheridium Spore MEIOSIS

Young gametophyte

Sporangium Archegonium Mature sporophyte

New sporophyte

Sperm

Egg Zygote

Sporangium

FERTILIZATION

Sorus 6 On the underside of the sporophyte‘s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia.

Gametophyte

Fiddlehead

25.5

5 A zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte.

4 Fern sperm use flagella to swim from the antheridia to eggs in the archegonia.

Transport in Xylem and Phloem • Vascular plants have two types of vascular tissue – Xylem and phloem

25.6

• Xylem – Conducts most of the water and minerals – Includes dead cells called tracheids

• Phloem – Distributes sugars, amino acids, and other organic products – Consists of living cells

25.6

Evolution of Roots • Roots – Are organs that anchor vascular plants – Enable vascular plants to absorb water and nutrients from the soil – May have evolved from subterranean stems

Evolution of Leaves • Leaves – Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis

Feeding the World • Seeds changed the course of plant evolution – Enabling their bearers to become the dominant producers in most terrestrial ecosystems

25.7

If a pollen grain germinates – It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule Female gametophyte (n) Egg nucleus (n)

Spore wall

Male gametophyte (within germinating pollen grain) (n)

Discharged sperm nucleus (n) Micropyle

25.7

Pollen grain (n)

Fertilized ovule. A megaspore develops into a multicellular female gametophyte. The micropyle, the only opening through the integument, allows entry of a pollen grain. The pollen grain contains a male gametophyte, which develops a pollen tube that discharges sperm.

• Pollen, which can be dispersed by air or animals – Eliminated the water requirement for fertilization – What did this mean?

25.7

–

The Evolutionary Advantage of Seeds A seed • Develops from the whole ovule • Is a sporophyte embryo, along with its food supply, packaged in a protective coat Seed coat (derived from Integument) Food supply (female gametophyte tissue) (n) Embryo (2n) (new sporophyte)

25.7

Gymnosperm seed. Fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument.

Gymnosperms • Gymnosperms - bear “naked” seeds, typically on cones – Among the gymnosperms are many wellknown conifers • including pine, fir, and redwood

25.8

Exploring Gymnosperm Diversity PHYLUM CYCADOPHYTA

PHYLUM GINKGOPHYTA

Cycas revoluta PHYLUM GNETOPHYTA

Gnetum

Ovulate cones

25.8

Welwitschia

Ephedra

Exploring Gymnosperm Diversity PHYLUM CYCADOPHYTA Douglas fir

Common juniper

Wollemia pine Pacific yew

Sequoia

Bristlecone pine

25.8

A Closer Look at the Life Cycle of a Pine • Key features of the gymnosperm life cycle include – Dominance of the sporophyte generation, the pine tree – The development of seeds from fertilized ovules – The role of pollen in transferring sperm to ovules 25.9

The life cycle of a pine

25.9

Angiosperms • Angiosperms – Are commonly known as flowering plants – Are seed plants that produce the reproductive structures called flowers and fruits – Are the most widespread and diverse of all plants

• The reproductive adaptations of angiosperms include flowers and fruits 25.10

Flowers • The flower – Is an angiosperm structure specialized for sexual reproduction

25.11

• A flower is a specialized shoot with modified leaves – Sepals, which enclose the flower – Petals, which are brightly colored and attract pollinators – Stamens, which produce pollen Carpel Stigma

Style Stamen – Carpels, which produce ovules Ovary Anther

Filament

Petal Sepal

25.11

Receptacle

Ovule

Fruits • Fruits

Tomato, a fleshy fruit with soft outer and inner layers of pericarp

Ruby grapefruit, a fleshy fruit with a hard outer layer and soft inner layer of pericarp

– Typically consist of a mature ovary Nectarine, a fleshy fruit with a soft outer layer and hard inner layer (pit) of pericarp

25.12

Milkweed, a dry fruit that splits open at maturity

Walnut, a dry fruit that remains closed at maturity

• Can be carried by wind, water, or animals to new locations, enhancing seed dispersal Wings enable maple fruits to be easily carried by the wind.

Seeds within berries and other edible fruits are often dispersed in animal feces.

25.12

The barbs of cockleburs facilitate seed dispersal by allowing the fruits to “hitchhike” on animals.

In the angiosperm life cycle – Double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule – One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates development of food-storing endosperm

• The endosperm – Nourishes the developing embryo 25.13

Angiosperm Life Cycle

25.13

Fossil Angiosperms • Primitive fossils of 125-million-year-old angiosperms – Display both derived and primitive traits Carpel Stamen

5 cm (a) Archaefructus sinensis, a 125-million-yearold fossil.

(b) Artist’s reconstruction of Archaefructus sinensis

Angiosperm Diversity • The two main groups of angiosperms – Are monocots and eudicots (dicots)

• Two minor groups include – Basal angiosperms • Are less derived and include the flowering plants belonging to the oldest lineages

– Magnoliids 25.14

• Share some traits with basal angiosperms but are more closely related to monocots and eudicots

Exploring Angiosperm Diversity BASAL ANGIOSPERMS

Amborella trichopoda

Star anise (Illicium floridanum)

Water lily (Nymphaea “Rene Gerard”)

MAGNOLIIDS

Southern magnolia (Magnolia grandiflora)

Eudicots

Monocots

Magnoliids

Star anise and relatives

Water lilies

Amborella

HYPOTHETICAL TREE OF FLOWERING PLANTS

Exploring Angiosperm Diversity

25.14

Evolutionary Links Between Angiosperms and Animals • Pollination of flowers by animals and transport of seeds by animals – Are two important relationships in terrestrial ecosystems

A flower pollinated by honeybees.

A flower pollinated by hummingbirds.

A flower pollinated by nocturnal animals.

Products from Seed Plants • Humans depend on seed plants for – Food – Wood – Many medicines