Dr. Mitch Pavao-Zuckerman Department of Ecology and Evolutionary Biology Diversity of Plants
621-8220 [email protected] Office hours: Biosciences West 431 W and F 1-2 p.m. or by appointment
Diversity of Plants (Fig 29.4) Monophyly Chlorophyta Ancestral Alga • Monophyletic group –includes the most recent common ancestor and all Nontracheophytes decendents
• These are NOT monophyletic: Nonseed Tracheophytes
Gymnosperms The Transition to Life on Land Angiosperms The Vascular Plants The Seed Plants The Flowering Plants
Green Plants Embryophytes (Land Plants) (viridiphytes) are a monophyletic group Land Plants are also a monophyletic group
• Photosynthetic eukaryotes that use • Green Plants include the chlorophyll a and b and store Chlorophytes (green algae) carbohydrates starch • Other green algae • and the land plants •Resting embryo with placental connection to the parent.
1 The Conquest of the Land The Conquest of the Land History of plants on land Early innovations in land plant • 500 mya - a few algae and lichens. evolution: • By 460 mya - primitive Land Plants, 1. cuticle (waxy coating) • By 425 mya - Early Vascular Plants were common 2. thick spore wall
• How did it happen? 3. Antheridia and archegonia •Obstacles? Reconstruction (gamete cases), 4. protected embryo Fossil 5. protective pigments – flavonoids absorb damaging UV light
Land Plants (Embryophytes) (Fig 29.4) Nontracheophytes:
Chlorophyta Ancestral Alga Liverworts, Hornworts, and Mosses
Nontracheophytes • Small plants (compared to present day Protected shrubs and trees) Embryos • Lack specialized water (xylem) and food Nonseed Tracheophytes conducting tubes (phloem) of vascular plants. Gymnosperms •Rely on diffusion of water and minerals.
Angiosperms Plant Kingdom?
Plant life cycles feature alternation of Nontracheophytes: generations (Fig 29.2) Liverworts, Hornworts, and Mosses
Multicellular Haploid • Diploid generation is Fig. 29.5 gametophyte smaller than the haploid generation Spore Gametes and • Diploid depends on it Haploid (n) for water and nutrition. Meiosis Fertilization Diploid (2n) • “The big green thing” Diploid Zygote is the haploid stage. •The diploid stage is attached to it. Multicellular sporophyte
2 Liverworts Hornworts (9,000 species) (100 species) • Lack stomates (pores with guard • Have stomates cells that regulate C02 uptake and • Horn-shaped spore producing H20 loss). diploid stage • Small spore producing diploid phase • One large flat chloroplast per cell compared to hornworts or mosses
What is not a common feature of non-vascular plants? Mosses (15,000 species) a. They are all relatively small • Have stomates • Spore producing upright diploid stage with capsule b. They all lack specialized conductive tissue such as xylem and phloem • Capsule has a lid and row of teeth that release the spores in wet weather. c. All possess stomata for gas exchange
d. The big generation is haploid (one set of chromosomes) with the smaller diploid (two sets of chromosomes) generation attached and dependent.
Land Plants (Embryophytes) (Fig 29.4) Vascular Plants Chlorophyta Ancestral Alga • Thick-walled dead water-conducting cells.
Nontracheophytes more efficient water movement Protected Embryos support for tall plants. Nonseed Tracheophytes Vascular tissue
Gymnosperms Vascular Plants (Tracheophytes) Angiosperms
3 Vascular Plants •The diploid generation became LARGER and independent of the haploid generation.
Figure 28.19
Figure 29.20
Tracheophytes Tracheophytes • Simple leaves may have evolved from the spore • The earliest producing structures. tracheophytes lacked roots. • Complex leaves may have evolved from a branching stem system. • Roots – possibly evolved from branches
Difference?
Land Plants (Embryophytes) (Fig 29.4) Nonseed Tracheophytes 1,200 species Chlorophyta Club mosses Ancestral Alga • Simple leaves Nontracheophytes • Cone-like structures with spores. Protected • Dominated tropical coastal swamps in Embryos Carboniferous period 300 myaÆ coal Nonseed Tracheophytes Vascular tissue deposits. • Selaginella is common here in the desert. Gymnosperms Vascular Plants (Tracheophytes) Angiosperms
4 Nonseed Tracheophytes Tracheophytes Whisk Ferns 15 species Horsetails 15 species • Simple branching like ancient vascular plants. • Jointed hollow stems •Tiny simple leaves Reconstruction of ancient • Silica deposits (“scouring rush”) • No true roots tracheophyte •Leaves in whorls • Spore sacs under “shields” on “cones”
Nonseed Tracheophytes What is not a common feature of Non-Seed Tracheophytes? Ferns 12,000 species •Big complex leaves with branching veins a. They are larger than non-vascular plants • Spores in sacs clustered on the bottom of the leaf •Tree ferns can reach 60 ft b. They possess specialized cells for moving water and • Leaves unfold from “fiddlehead” food
c. All possess stomata for gas exchange
d. The big generation is haploid (the gametophyte with one set of chromosomes)
Land Plants (Embryophytes) (Fig 29.4) Seed Plants 300,000 species Chlorophyta Ancestral Alga • The seed plants have greatly reduced haploid stage. Nontracheophytes Protected • How did this happen? Embryos Fig 30.2 Nonseed Tracheophytes Vascular tissue
Seeds Gymnosperms
Seed plants Angiosperms
5 How did seeds evolve? Seed Plants 300,000 species • Ancestors of seed plants had one kind of spore. • First dimorphic spores evolved:
• Further reduced haploid generation. Microspores (grow into sperm producing haploid stage) Part of the evolution of seeds Megaspores (grow into egg producing haploid stage) and pollen. • Megaspores reduced to just one. • Seeds - protected resting stage opening many possibilities, like suspended animation. Spore sac •Pollen - sperm delivery system; escape the need of water for sperm to swim.
How did seeds evolve? Pollen is a reduced male haploid stage • Megaspore enveloped in a sac. Diploid Haploid Plant and flower are diploid Spore sac Spores • Female haploid stage grows in this “seed”. Reduced haploid • It is attached to the diploid parent. stage
Pollination Seed Plants 300,000 species 1. Pollen Æ reduced haploid female. 2. Pollen produce sperm to fertilize an egg. 3. The zygote develops into a seed embryo. • So, seed plants make seeds and pollen •Also make wood. • Evolved ~ 370 mya
6 Land Plants (Embryophytes) (Fig 29.4) Seed Plants - Gymnosperms Chlorophyta Ancestral Alga • Gymnosperm = ‘naked seeded’ Nontracheophytes Protected • Do not have flowers or fruit tissue Embryos Nonseed Tracheophytes Vascular tissue
Seeds Gymnosperms
Angiosperms
Gymnosperms - 4 Phyla Gymnosperms - Conifers Cycads Ginkos • Leaves often “evergreen” needles or scales •Cones: scales with seeds
Gnetophytes
Seed Plants- Conifers Land Plants (Embryophytes) (Fig 29.4) Chlorophyta • Longest-lived trees - Bristlecone Ancestral Alga pine: 5,000y Nontracheophytes • Tallest tree – redwood 112 m Protected • Most massive tree – sequoia – 11m Embryos wide Nonseed Tracheophytes Vascular tissue
Seeds Gymnosperms
Flowers Angiosperms
Flowering Plants
7 Seed Plants - Angiosperms Seed Plants - Angiosperms Pollination • Highly diverse plant phylum • Pollen lands on stigma, rather than at the • Dominant form of plant life on Earth tip of the ovule • Reduces chance of self-pollination – • Because of differences from other plants increases genetic diversity
Fig 30.7, 30.11
Double fertilization (producing zygote and endosperm) Endosperm Seed Plants Angiosperms Nucleus
• Fruit and stamens evolved from leaf-like structures.
• Flowers and fruit are unique features
Seed Plants - Angiosperms Seed Plants Angiosperms
• Much diversity is related to pollination and dispersal mechanisms.
8 Review Land Plants (Fig 29.4)
Chlorophyta Ancestral Alga
Nontracheophytes Protected Embryos Nonseed Tracheophytes Vascular tissue
Seeds Gymnosperms
Flowers Plant Kingdom? Angiosperms Tracheophytes? Seed plants?
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