Chapter 23: Plant Evolution
In order to survive the transition from water to land it was necessary for plants to make
adaptations for obtaining water and to prevent its loss. Water was also required to
provide a medium for the fertilization of eggs by flagellated sperm. In addition, once
plants emerged from the protective cover of water, genetic material was more
susceptible to damage by UV radiation. The following list summarizes the major plant
adaptations for survival on land.
Overview of the Plant Kingdom
 295,000 species of photoautotrophs
 a few heterotrophs
 vascular plants – internal tissues conduct water and solutes through roots, stems
and leaves
 bryophytes – nonvascular plants
 Ex. Liverworts, hornworts, and mosses
 Gymnosperms – seed bearing vascular plants
 Angiosperms – seed and flower bearing vascular plants
 2 groups – dicots and monocots
23.2 Evolutionary Trends Among Plants
Roots, Stems and Leaves
 root system – underground absorptive structures and help anchor plant
 shoot system – aboveground stems and leaves
 lignin – an organic compound in cell walls that inables the stems to support
themselves
 xylem – distributes water and dissolved ions to cells
 phloem – distributes dissolved sugars and other photosynthetic products
 cuticle – a waxy coat to help conserve water
 stomata – tiny openings across the surface of leaves, help control the absorption of
carbon dioxide and restrict evaporation.
From Haploid to Diploid Dominance
 in most plant life cycles, the diploid phase dominates
 sporophyte – multicelled diploid body, male and female gametes fused
 some cells of sporophytes undergo meiosis and give rise to haploid cells called
spores
 spores divide by mitosis and give rise to gametophytes
 Gametophytes – haploid multicelled body in which haploid gametes form
 the shift to diploid dominance was an adaptation to land habitats, because the
climate changed so much
Evolution of Pollen and Seeds
 Bryophytes – non vascular
 Vascular, seedless, make 1 type of spore (homosporous)
 Lycophytes
 Horsetails
 Ferns
 Vascular, seeds, make 2 types of spores (heterosporous)
 Gymnosperms
 Cycads
 Ginkgos
 Gnetophytes
 Conifers
 Vascular, seeds, flowers
 Angiosperms
 Heterosporous
 Megaspores – form female gametes
 Microspores – form pollen grains, sperm-bearing male gamete
 Pollen grains travel to the egg by way of air or animals
 Embryo sporophytes packaged into seeds
23.3 The Bryophytes – No Vascular Tissues
 Ex. mosses. Liverworts, and hornworts
 nonvascular plants
 grow in moist habitats
 mosses are sensitive to air pollution
 do not contain xylem and phloem (no need because they live in a moist habitat)
 peat bogs
 accumulative remains of mosses compressed into mats
 highly acidic
 hampers bacteria and fungal growth
 absorbs 5X more H2O than cotton
 Rhizoids – elongated cells or threadlike structures that attach gametophytes to the
soil and serve as absorptive structures
23.4 Seedless Vascular Plants (Tracheophytes)
 Ex. whisk ferns, lycophytes, horsetails and ferns
 have vascular tissues
 seedless
 live in wet humid places
 water droplets on plants are the only way flagellated sperm can reach eggs
 all produce spores that germinate into small gametophytes
 4 types
1. Whisk Ferns (Psilophyta)
 Not a fern
 Resemble a whisk broom
 Rhizomes – branching, short, horizontal absorptive stem that grow
underground
2. Lycophytes
 Club mosses – club shaped spore-bearing cones or strobili
 Vascularized stems and roots which grow from a branching underground
rhizome
 Strobilus – leaves are organized around a central stem
3. Horsetails (Sphenophyta)
 Thrive in streambank muds, vacant lots, roadsides
 rhizomes
 Hollow stems
 Silica – reinforced ribs structurally support these stems and give them texture
 A cylinder of xylem and phloem runs parallel with the stems
 Stems have horizontal ribs reinforced with silica
4. Ferns (Pterophyta)
 Largest most diverse group of seedless vascular plants
 Sori – clusters of sporangia develop on underside of fern fronds
 Epiphytes – any aerial plant that grows attached to tree trunks or branches.
23.7 Gymnosperms – Plants with “Naked Seeds”
☺ Vascular
☺ Naked seeds
1. Conifers
 Woody trees and shrubs
 Needlelike or scalelike leaves
 Cones – female reproductive structure with many ovules
 Ex. Pines, redwoods, firs, spruces, cypress
2. Cycads
 Pollen bearing and seed bearing cones form on separate plants
 Inhabit tropical and subtropical
3. Ginkgos
 Deciduous – shed leaves
 Only surviving species is Ginkgo biloba
A Representative Life Cycle
 Scales of pine cones are parts of a mature female cone in which megaspores
formed and developed into female gametophyte
 Species of pines, fertilization occurs months or a year after pollination
 Pollen grains are released and land on the female come
 Pollen grain germinates and grows a tubular structure
 It grows slowly through the ovule’s tissue for about a year
 Penetrates the female gametophyte and sperm reaches egg and fertilization occurs
23.8 Angiosperms – The Flowering, Seed-Bearing Plants
 Flowers – specialized reproductive structures
 Pollinators – insects, birds, bats, etc
 Flowering plants coevolved with pollinators
 Three classes of flowering plants
1. Magnoliids – avocado trees, nutmeg trees
2. monocots – orchids, palms, lilies, and grasses, including rye, sugarcane, corn,
rice, wheat, etc.
3. eudicots – cabbages, daisies, most flowering shrubs and trees, oaks, apple, cacti
Chapter 23: Plant Evolution
In order to survive the transition from water to land it was necessary for plants to make
adaptations for obtaining water and to prevent its loss. Water was also required to
provide a medium for the fertilization of eggs by flagellated sperm. In addition, once
plants emerged from the protective cover of water, genetic material was more
susceptible to damage by UV radiation. The following list summarizes the major plant
adaptations for survival on land.
Overview of the Plant Kingdom
 ____________ species of photoautotrophs
 A few heterotrophs
 Vascular plants –
 Bryophytes –

 Gymnosperms –
 Angiosperms –
 3 groups –
23.3 Evolutionary Trends Among Plants
Roots, Stems and Leaves
 Root system –
 Shoot system –
 Lignin –
 Xylem –
 Phloem –
 Cuticle –
 Stomata –
From Haploid to Diploid Dominance
 In most plant life cycles, the diploid phase dominates
 Sporophyte –
 Some cells of sporophytes undergo meiosis and give rise to haploid cells called
spores
 Spores divide by ____________ and give rise to _________________
 Gametophyte –
 The shift to diploid dominance was an adaptation to land habitats, because the
climate changed so much
Evolution of Pollen and Seeds
 Bryophytes – non vascular
 Vascular, seedless, make 1 type of spore (homosporous)
 Lycophytes
 Horsetails
 Ferns
 Vascular, seeds, make 2 types of spores (heterosporous)
 Gymnosperms
 Cycads
 Ginkgos
 Conifers
 Vascular, seeds, flowers
 Angiosperms
 Heterosporous
 Megaspores – form female gametes
 Microspores – form pollen grains, sperm-bearing male gamete
 Pollen grains travel to the egg by way of air or animals
 Embryo sporophytes packaged into seeds
23.3 The Bryophytes – No Vascular Tissues
 Ex.
 Nonvascular plants grow in moist habitats

 Mosses are sensitive to air pollution
 Do not contain __________ and __________ (no need because they live in a moist
habitat)
 Peat bogs
 Accumulative remains of mosses compressinto mats

 Hampers ____________ and ____________ growth
 Absorbs _____ more H2O than cotton
 Rhizoids –
23.4 Seedless Vascular Plants (Tracheophytes)
 Ex.
 Have _______________ tissues

 Live in humid places
 Water droplets on plants are the only way flagellated sperm can reach eggs
 All produce spores that germinate into small gametophytes
 4 types
1. Whisk Ferns (Psilophyta)


 Rhizomes -
2. Lycophytes
 Club mosses –
 Vascularized stems and roots which grow from a branching underground
rhizome
 Epiphytes –
3. Horsetails (Sphenophyta)
 Thrive in

 Hollow stems
 A cylinder of xylem and phloem runs parallel with the stems
 Stems have horizontal ________ reinforced with __________
4. Ferns (Pterophyta)
 Largest most diverse group of seedless vascular plants
 Sori –
 Epiphytes – any aerial plant that grows attached to tree trunks or branches.
23.7 Gymnosperms – Plants with “Naked Seeds”


1. Conifers

 Needlelike or scalelike leaves
 Cones –
 Ex.
2. Cycads
 __________ bearing and __________ bearing cones form on separate plants

3. Ginkgos
 Deciduous –
 Only surviving species is __________ __________
A Closer Look at the Conifers
 Scales of pine cones are parts of a mature female cone in which megaspores
formed and developed into female gametophyte
 Species of pines, fertilization occurs months or a year after pollination
 Pollen grains are released and land on the female ________
 Pollen grains _______________ and grows a tubular structure
 It grows slowly through the ovule’s tissue for about a year
 Penetrates the female gametophyte and sperm reaches egg and _______________
occurs
23.8 Angiosperms – The Flowering, Seed-Bearing Plants
 Flowers –
 Pollinators –
 Flowering plants coevolved with pollinators
 Three classes of flowering plants
1. Magnoliids –
2. Monocots –
3. Eudicots –