Download 5. Plant diversity

PLANT EVOLUTION AND DIVERSITY
Plants evolved from green algae
• Molecular, physical, and chemical evidence
LM 444 
– Indicates that green algae called
charophyceans are the closest living
relatives of plants
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
Reproductive structures, as in flowers,
contain spores and gametes
Leaf performs photosynthesis
Cuticle covering leaves and stems
reduces water loss; stomata in
leaves allow gas exchange
Stem supports plant and may
perform photosynthesis
Surrounding water
supports alga
Roots
anchor plant;
absorb water and
minerals from
the soil
Alga
Whole alga
performs
photosynthesis;
absorbs water,
CO2, and
minerals from
the water
Holdfast
anchors alga
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Land plants
Vascular plants
Gymnosperms
Pterophytes
(ferns and relatives)
Angiosperms
Seed plants
Seedless vascular plants
Lycophytes
(club mosses and
relatives)
Mosses
Hornworts
Liverworts
Bryophytes
(nonvascular plants)
Origin of seed plants
(about 360 mya)
Origin of vascular plants
(about 420 mya)
Origin of land plants
(about 475 mya)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Bryophytes lack vascular tissue and include
– The mosses, hornworts, and liverworts
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The zygote develops into the diploid sporophyte
– In which meiosis produces haploid spores
• Spores grow into gametophytes
• Alternation of generations
Key
Gametophyte
plant (n)
Haploid (n)
Diploid (2n)
Sperm
Spores (n)
Egg
Gametes (n)
Meiosis
Fertilization
Zygote (2n)
Sporophyte
plant (2n)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Gametophytes (n)
Key
1
Haploid (n)
Diploid (2n)
Male
Mitosis and
development
5
Sperm (n) (released
from gametangium)
Spores (n)
1
Female
Egg (n)
Fertilization
Sporangium
Stalk
Meiosis
4
Sporophytes (growing
from gametophytes)
2
Zygote (2n)
Sporophyte (2n)
3
Mitosis and
development
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Division Marchantiophyta “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 in
Doctrine of Signatures and lobed thallus indicated
plants 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 Photograph
by Brian Scoggins
Ex. Marchantia (after French botanist)
-reproduce asexually by gemmae cups that act as rain
splashcups dispersing tiny clones
Sexual reproduction is similar to mosses except gameteangia
and 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 green
horn-like sporangium
-rare in Texas wetlands.
One population of yellow
hornwort known from
Ottine Wetlands in
Gonzales County, Texas
near Palmetto State Park
Some human and ecological importance of bryophytes
1. Pioneer organisms
2. Sphagnum or peat moss
-used as fuel
-used as soil conditioner as can
-absorb about 25X weight in
water
-smoky peat fires used flavor
barley used in making Scotch
Whiskey
3. Many species are good
indicators of air and water pollution