Plant Diversity The Evolution of Land Plants Ch 30 (from the edge of the swamp…) •From Sea to Land • Origins, Relationships, Diversity • Shared Derived Traits Videos 28-3, 28-5 (Synapomorphies) • Nonvascular to Vascular Plants •chlorophylls a and b • Seedless to Seeds
03 March 2009 Green stuff ECOL 182R UofA K. E. Bonine 1 2
Original Land Plants Related to Algae Land Plants are Monophyletic Land plants retain derived features they share with green algae (Charales): Land plants are monophyletic, all • Chlorophyll a and b. descend from a single common •Starchas a storage product. ancestor. • Cellulose in cell walls.
One synapomorphy: development from an embryo protected by tissues of the parent plant. Therefore, also called embryophytes.
See Figure 30.9 3 (phyton = plant) 4
Land Plants Comprise ~Ten Clades Moving to Land Plants first appeared on land between Nonvascular (3 clades) 400–500 million years ago. -paraphyletic group -liverworts, Environmental Challenges: -hornworts 1. dessication -mosses 2. transport water to all parts 3. support (fight gravity) Vascular plants, or tracheophytes 4. disperse gametes. (7 clades)—all have conducting cells called -tracheids. Some challenges met immediately, -monophyletic group 5 others took millions of years 6
1 Biological history Biological history
Earth forms Origin of Life
Photo- synthesis evolves
Eukary- Multi- otic cellular cells
Abundant life Moss Plants first appeared on land between 400–500 million years ago. First land Forests Birds Aquatic life plants Insects Flowering First plants Abundant mammals Rise of fossils First land animals Dinosaurs Mammals First hominids dominant 7 Homo sapiens 8
Adaptations for Land Plants Help Create Soil 1. Cuticle - waxy covering that retards water loss Ancient plants contributed to soil 2. Gametangia enclosing gametes formation. 3. Embryos in a protective structure Acids secreted by plants help break 4. Pigments that protect against UV down rock. radiation Organic material from dead plants 5. Spore walls containing sporopollenin contributes to soil structure. -resistsdesiccation and decay Create habitat and pave way for 6. Mutualistic relationships with fungus succession of other species. - to promote nutrient uptake from soil 9 10
Nonvascular Plants Are Traits of Nonvascular Plants Similar to Ancestral Land Plants Growth pattern of Today’s nonvascular plants are nonvascular plants allows thought to be similar to the water to move through first land plants. mats by capillary action. They grow in moist Minerals can be environments in dense mats distributed through the small plants by diffusion. They are small, there is no system to conduct water Mutualistic relationship from soil to plant body parts. with fungi called glomeromycetes which mosses promote absorption of mosses 11 water and minerals. 12
2 Extant Plants See Figure 30.9 Three Nonvascular Clades (paraphyletic group)
Hornworts Discuss ancestral first, Mosses then derived
Alternation of Generations Moss Lifecycle (Nonvascular Plant) Water required Size and for egg and independence of sperm to meet gametophyte or sporophyte gametophyte, 1n changes
All plants have alternation of Sporophyte (2n) sporophyte, 2n dependent on, generations and attached to, (= multicellular gametophyte See Figure haploid & multicelluar 30.17 See Figure diploid) 30.1615 16
Nonvascular: Gametophyte Nonvascular Plant Reproduction Dominates Male: antheridium Female: archegonium In nonvascular plants: gametophyte is larger, longer-lived, and more self-sufficient than the sporophyte.
gametophyte generation is photosynthetic.
sporophyte may or may not be photosynthetic, but is always nutritionally dependent on the gametophyte, and is permanently attached.
Reduction of the gametophyte generation is a 17 See Figure 18 major theme in plant evolution. 30.17
3 Nonvascular Plant Nonvascular Diversity Reproduction Hornworts: Anthocerophyta—100 species. Gametophytes are flat plates of cells. Base of archegonium grows to Have stomata, which do not close. protect embryo during early Hornwort cells have a single, large development. chloroplast. The sporophyte has no stalk; but has a basal region capable of infinite cell (land plants aka embryophytes) division. Sporophytes can grow up to 20 cm. Hornworts have internal cavities filled 19 with nitrogen-fixing cyanobacteria. 20
Moss… Life cycle of a moss
Sphagnum grows in swampy places. The upper layers of moss compress lower layers that are beginning to decompose, forming peat. Video Long ago, continued compression led to 28-3 the formation of coal. Mosses are sister group to vascular plants
Harvesting Peat from a Bog
Navajo Power Plant, Page, AZ
4 Paleozoic: Carboniferous Vascular Plants Arose from • Large glaciers and swamp forests of Nonvascular treeferns and horsetails.
• Fossilized Recently, fossilized fragments of forests ancient liverworts have been formed the discovered. coal we now mine for energy.
Vascular Plants Comprise Seven Seedless Vascular Plants Clades 10 clades of land plants: 1 Nonvascular (3 clades) 2 -liverworts, hornworts, and mosses 3 -paraphyletic group 4 5
Vascular plants, or tracheophytes 6 (7 clades) 7 8 -conducting cells called tracheids. 9 10 -monophyletic group 27 28
Traits of Vascular Plants Extant Plants The vascular system consists of tissue specialized for the transport of materials.
Xylem conducts water and minerals from soil up to aerial parts of plant. Some cells have lignin—provides support. Tracheids are the main water-conducting Vascular, but element in xylem. Angiosperms have tracheids Seedless plus a more efficient system of vessels and
fibers. See Fig 30.12
Phloem conducts products of photosynthesis
through plant. 29 30
5 Evolution of Vascular Plants Evolution of Vascular Plants Earliest vascular plants (now Vascular plants have a branching, extinct): Rhyniophytes (Silurian) had independent sporophyte. dichotomous branching, but Mature sporophyte is nutritionally lacked leaves and roots. They were anchored by rhizomes independent from the (horizontal portions of stem) gametophyte. and rhizoids (water-absorbing filaments).
Earliest vascular Still must have water for part of the life cycle— plants had no true for the flagellated, swimming sperm. 31 roots. 32
Evolution of Vascular Plants Evolution of Vascular Plants Lycophytes appeared in the Silurian. Pteridophytes appeared in the Devonian. Leaf: a flattened photosynthetic These groups had true roots and structure arising from a stem or leaves, and two types of spores. branch; has true vascular tissue. Two types: microphylls and megaphylls. Overtopping evolved --new branches grow beyond the others—an advantage in the competition for light
Evolution of Leaves Evolution of Vascular Plants
Small megaphylls first appeared in the Devonian. Large megaphylls did not Horsetails: Fifteen species appear until the Carboniferous. in one genus—Equisetum. One theory: high CO2 concentrations in Silica in cell walls—“scouring the Devonian prevented development rushes.” of stomata. Have true roots; sporangia Stomata allow heat to be lost by the are on short stalks called evaporation of water. Large leaves sporangiophores. with no stomata would have resulted in Leaves are reduced overheating. megaphylls in whorls. Each stem segment grows from 35 the base. 36
6 Figure 28.17 Horsetails Evolution of Vascular Plants
Ferns: 12,000 species. About 97 percent are in a clade— leptosporangiate ferns—sporangia walls only one cell thick, borne on a stalk. Sporophytes have true roots, stems, and leaves. Fern leaf starts development as a coiled “fiddlehead.”
Figure 28.19 Fern Leaves Take Many Forms Ferns… Most ferns are in shaded, moist environments. Tree ferns can reach heights of 20 m. Sporangia occur on undersides of leaves in clusters called sori. Most ferns are homosporous; two groups of aquatic ferns are heterosporous. Some genera have a tuberous gametophyte that depends on a mutualistic fungus for nutrition.
The Life Cycle of Mature gametophyte Life cycle of a fern (about 0.5 cm wide) a Homosporous Archegonium
Fern Egg Video Germinating Rhizoids 28-5 spore Antheridium Sperm
Sporophyte and HAPLOID (n) Meiosis Fertilization Gametophyte are DIPLOID (2n) each free-living Sporangium Embryo Microsorum sp. Sporophyte
Sori (clusters Mature sporophyte Roots Vascular but Seedless of sporangia) (typically 0.3–1 m tall)
7 Ferns… Early Vascular Plants
During the Permian, the continents DNA research suggests that came together to form Pangaea. diversification of modern ferns is Extensive glaciation occurred late in fairly recent. the Permian. Ferns may have taken advantage of Lycophyte–fern forests were replaced shady environments created by by gymnosperms. angiosperm trees.
Bristlecone Pine Bristlecone Pine The oldest known tree is "Methuselah", which is 4,789 years old. To keep Methuselah from harm, this tree isn't labeled, as the other trees are. An older tree If you could imagine a living tree as old as the pyramids called Prometheus was killed shortly after it was of Egypt, what do you think it would look like? It would discovered in 1964. This happened when a geologist look like a bristlecone pine, Pinus longaeva, the oldest searching for evidence of Ice Age glaciers was taking known tree species in the world. some core samples from several bristlecones. Just as The bristlecone pine only lives in scattered, arid mountain he realized he had found a tree over 4,000 years old, regions of six western states of America, but the his coring tool broke. Amazingly the U.S. Forest oldest are found in the Ancient Bristlecone Pine Forest Service gave him permission to cut down the tree. in the White Mountains of California. There the pines Prometheus turned out to be 4,950 years old. It was a exist in an exposed, windswept, harsh environment, 300 year old tree when the pyramids were being built free of competition from other plants and the ravages in Egypt. of insects and disease. The oldest bristlecones usually Laboratory of Tree-Ring Research 45 46 grow at elevations of 10,000 to 11,000 feet. http://www.ltrr.arizona.edu/
Which of the following are vascular plants? a Juniper b Sunflower c Fern d Moss e Horsetail f Liverwort g Lily