PLANT EVOLUTION AND DIVERSITY Plants evolved from green algae Molecular, physical, and chemical evidence –Indicates that green algae called charophyceans

PLANT EVOLUTION AND DIVERSITY

Plants evolved from green algae

• Molecular, physical, and chemical evidence

– Indicates that green algae called charophyceans are the closest living relatives of plants

LM 4

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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Plants and algae share the following characteristics

-chlorophyllous-store energy mainly as starch-cellulose cell walls-form cell plates during cell division-primitive plants have flagellated sperm like algae

Plants have adaptations for life on land

Plants are multicellular photosynthetic eukaryotes

Plants have some specific adaptations that are not found in algae

Plant

Rootsanchor plant;absorb water andminerals fromthe soil

Reproductive structures, as in flowers,contain spores and gametes

Cuticle covering leaves and stemsreduces water loss; stomata inleaves allow gas exchange

Leaf performs photosynthesis

Surrounding watersupports alga

Stem supports plant and mayperform photosynthesis

Whole algaperformsphotosynthesis;absorbs water,CO2, andminerals fromthe water

Holdfastanchors alga

Alga


Plants have apical meristems

– Are the growth-producing regions of a plant

– Help maximize exposure to the resources in the soil at root tip and air at buds

Plants have vascular tissue

– distributes nutrients throughout Pteridophytes, Gymnosperms, and Angiosperms


Plants have secondary cell walls

The secondary cell walls of some plant tissues provide support

– are thickened and strengthened by lignin, a polymer of alcohols that is extremely strong forming secondary cell walls

Plants have a cuticle and stomates/lenticels

• A waxy cuticle covers the stems and leaves of plants

– And helps retain water

• Stomata/lenticels

– Are tiny pores in leaves that allow for gas exchange

Many living plants can reproduce on land

– Produce gametes that are encased in protective structures called ovules and pollen grains

– Most gymnosperms and all angiosperms have nonflagellated sperm

Plant diversity reflects the evolutionary history of the plant kingdom

• Some highlights of plant evolution

Origin of vascular plants(about 420 mya)

Origin of seed plants(about 360 mya)

Origin of land plants(about 475 mya)

Seed plants

Land plants

Bryophytes(nonvascular plants)

Vascular plants

Seedless vascular plantsLi

verw

orts

Hor

nwor

ts

Mos

ses

Lyco

phyt

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lub

mos

ses

and

rela

tives

)

Pte

roph

ytes

(fer

ns a

nd r

elat

ives

)

Ang

iosp

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Gym

nosp

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s


• Bryophytes lack vascular tissue and include

– The mosses, hornworts, and liverworts


• Vascular plants

– Have supportive vascular tissues such as xylem that carries water and minerals and phloem that conducts carbohydrates

– Pteridophytes and most gymnosperms have xylem tracheids and most woody gymnosperms have softwood

– Gymnosperms called gnetophytes and angiosperms have tracheids and thick-walled vessels and if woody are called hardwoods

• Pteridophytes are seedless vascular plants

– With flagellated sperm


• Seed plants

– Have pollen grains that transport sperm

– Protect their embryos in ovules that grow into seeds

– Seeds are better adapted than single-celled spores having a coat, stored carbohydrate, and an embryo

• Gymnosperms, such as pines

– Produce seeds in cones


• The seeds of angiosperms

– Develop within protective ovaries


Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

ALTERNATION OF GENERATIONS AND PLANT LIFE CYCLES

Haploid and diploid generations alternate in plant life cycles

• The haploid gametophyte

– Produces eggs and sperm by mitosis

• The zygote develops into the diploid sporophyte

– In which meiosis produces haploid spores

• Spores grow into gametophytes

• Alternation of generations

Sporophyteplant (2n)

Key

Fertilization

Gametophyteplant (n)Haploid (n)

Diploid (2n)

Sperm

Egg

Mitosis

Zygote (2n)

Gametes (n)

Spores (n)

Mitosis

Mitosis

Meiosis


Mosses have a dominant gametophyte

• A mat of moss is mostly gametophytes

– Which produce eggs and swimming sperm

• The zygote develops on the gametophyte

– Grows into the smaller sporophyte

Characteristics of Bryophytes or Nonvascular plants

-no vascular tissue absorbing water by capillarity and transporting carbohydrates by diffusion

-no true roots, stems, or leaves as lack vascular tissue.Rhizoids are root-like but are only used for anchorage.

-Alternation of generations and gametophyte dominates with gametes formed inside multicellular gameteangia called antheridia or archegonia

-biflagellate sperm that require water for successful fertilization

Division Bryophyta “moss plant” @12,000 sps.

-gametophytes have rhizoids, an erect stem-like body, and leaf-like organs

-often found in damp or aquatic habitats

-reproduce asexually by fragmentation

Sexual reproduction:

• Life cycle of a moss

KeyHaploid (n)

Diploid (2n)

Spores (n)Egg (n)

Sperm (n) (releasedfrom gametangium)

Sporophytes (growingfrom gametophytes)Meiosis

Sporangium

Female

Gametophytes (n)

Fertilization

Stalk

Sporophyte (2n)

Male

Zygote (2n)

1

1

2

Mitosis anddevelopment

3

4

Mitosis anddevelopment

5


Division Hepatophyta “liver plant” @6500 sps.-20% gametophytes have a flattened body called thallus and 80% have erect growth like mosses but the stalk of the sporophyte is translucent to white; its capsule is typically black and egg-shaped. When it matures, the capsule splits open into four equal quarters, releasing the spores to the air. -in medieval (476-1450) period, people believed inDoctrine of Signatures and lobed thallus indicatedplants were treatment for liver disease-often found in damp or aquatic habitats and are primarily tropical in range

Liverwort on Colorado River near Bend, Texas Photographby Brian Scoggins

Ex. Marchantia (after French botanist)-reproduce asexually by gemmae cups that act as rain splashcups dispersing tiny clonesSexual reproduction is similar to mosses except gameteangiaand sporangia grow in umbrella-like structures called _____ and _____ and spores have elaters that curl and uncurl due to changes in humidity

Phylum Anthoceratophta “Flowering horn plants” 100spp.-mostly tropical-Reproduce asexually by fragmentation and sexually like mosses except with greenhorn-like sporangium -rare in Texas wetlands. One population of yellowhornwort known from Ottine Wetlands in Gonzales County, Texas near Palmetto State Park

Some human and ecological importance of bryophytes

1. Pioneer organisms2. Sphagnum or peat moss-used as fuel-used as soil conditioner as can -absorb about 25X weight in water-smoky peat fires used flavorbarley used in making ScotchWhiskey3. Many species are good indicators of air and water pollution

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PLANT EVOLUTION AND DIVERSITY Plants evolved from green algae Molecular, physical, and chemical evidence –Indicates that green algae called charophyceans