Ch30PwrPtFall07

Plant Diversity IIThe Evolution of Seed Plants: 

Chapter 30 Plant Diversity II The Evolution of Seed Plants

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Fig. 29.7 Bryophytes (nonvascular plants) Seedless vascular plants Seed plants Vascular plants Land plants Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Charophyceans Liverworts Hornworts Mosses Lycophytes (club mosses etc.) Pterophyte (ferns, horsetails, whisk fern) Gymnosperms Angiosperms Hashed lines indicate uncertainties Plant Origins Seed plants appeared ~360 m.y.a. with the rise of the Gymnosperms Flowering plants (Angiosperms) – the other surviving lineage – appeared ~200 million years later

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Fig. 30.2 Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent

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Fig. 30.2 Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Seedless vascular plants Sporophyte dominant; sporophyte initially dependent; gametophyte independent

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Angiosperms Gametophytes develop inside flowers Fig. 30.2 Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Seedless vascular plants Sporophyte dominant; sporophyte initially dependent; gametophyte independent Seed plants Sporophyte dominant; sporophyte independent; gametophyte dependent & microscopic Gymnosperms Gametophytes develop inside cones

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Fig. 30.2 Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Seedless vascular plants Sporophyte dominant; sporophyte initially dependent; gametophyte independent Seed plants Sporophyte dominant; sporophyte independent; gametophyte dependent & microscopic Gametophytes develop from spores retained within sporangia of the parental sporophyte

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Seed plants See diagram on pg. 586 Heterosporous spore production (some seedless vascular plants; all seed plants) Megasporangium in megasporophyll (2n) Megaspore (n) Female Gametophyte (n) Microsporangium in microsporophyll (2n) Microspore (n) Male Gametophyte (n) Eggs (n) Sperm (n)

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Seed plants Fig. 30.3 Unfertilized ovule Integument Spore wall Megaspore (n) Megasporangium (2n) In this example we are using a pine cone Layers of integuments envelope and protect the megasporangium The whole structure – megasporangium, megaspore, and integuments – is called an ovule A megaspore develops into a multicellular female gametophyte

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Spore wall Male gametophyte (pollen grain) (n) Female gametophyte (n) Egg nucleus (n) Discharged sperm nucleus (n) Micropyle Seed plants Fig. 30.3 A megaspore develops into a multicellular female gametophyte Fertilization initiates the transformation of the ovule into a seed

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Seed coat (derived from Integument) Food supply Embryo (2n) (new sporophyte) Seed plants Fig. 30.3 Fertilization initiates the transformation of the ovule into a seed Compared to a single-celled spore, a seed is much more resistant and complex

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“Naked seeds”; not enclosed by an ovary and develop on the surface of modified leaves that usually form cones (strobili) Gymnosperms

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Phylum Ginkgophyta Ginkgo biloba is the only living species of this entire phylum Gymnosperms

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Phylum Cycadophyta (cycads, sago palms) Thrived during the “Age of Dinosaurs”; only ~130 species alive today Gymnosperms

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Phylum Cycadophyta (cycads, sago palms) Thrived during the “Age of Dinosaurs”; only ~130 species alive today Gymnosperms ♀ ♂

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Phylum Gnetophyta 3 genera: Gnetum Gymnosperms

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Phylum Gnetophyta 3 genera: Gnetum Ephedra Gymnosperms

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Phylum Gnetophyta 3 genera: Gnetum Ephedra Welwitschia Gymnosperms

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Phylum Coniferophyta E.g., longleaf pine Gymnosperms

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Phylum Coniferophyta E.g., longleaf pine Gymnosperms KEH note: For future this might be a good place to stop and give an overview of my research and the plight of longleaf.

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Phylum Coniferophyta E.g., longleaf pine, giant sequoia Gymnosperms

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Phylum Coniferophyta E.g., longleaf pine, giant sequoia, cypress Gymnosperms

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Phylum Coniferophyta E.g., longleaf pine, sequoia, cypress, and ~600 other cone-bearing species Gymnosperms

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Meiosis Fertilization Key Haploid Diploid Gametophytes Egg Sporophyte Meiosis Gymnosperms (e.g., pine) Ovulate cone Pollen cone Megasporangium Microsporangium Megasporangia and microsporangia are found in separate cones Meiosis produces spores and begins the haploid generation Fig. 30.6 Megasporocytes (2n) are the cells within megasporangia that undergo meiosis to produce megaspores (n) Microsporocytes (2n) are the cells within microsporangia that undergo meiosis to produce microspores (n) Megasporocyte Microsporocyte

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Meiosis Fertilization Key Haploid Diploid Gametophytes Egg Sporophyte Meiosis Gymnosperms (e.g., pine) Ovulate cone Pollen cone Megasporangium Microsporangium Fig. 30.6 Megasporocyte Microsporocyte Each megaspore develops into a female gametophyte Each microspore develops into a male gametophyte (a pollen grain) Megaspore Pollen A pollen grain gains access to a female gametophyte through a micropyle

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Meiosis Fertilization Key Haploid Diploid Gametophytes Megaspore Sporophyte Meiosis Gymnosperms (e.g., pine) Ovulate cone Pollen cone Megasporangium Microsporangium Fig. 30.6 Megasporocyte The female gametophyte contains 2 or 3 archegonia, each with 1 egg cell Two cells of the male gametophyte are sperm Microsporocyte Pollen Archegonium Egg nuclei Sperm nuclei

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Meiosis Fertilization Key Haploid Diploid Gametophytes Embryo Sporophyte Meiosis Gymnosperms (e.g., pine) Ovulate cone Pollen cone Fertilization (union of 1 egg and 1 sperm) produces an embryo Megasporangium Microsporangium Fig. 30.6 Megaspore Microsporocyte Pollen Megasporocyte Archegonium Egg nuclei Sperm nuclei

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Meiosis Fertilization Key Haploid Diploid Gametophytes Embryo Sporophyte Meiosis Gymnosperms (e.g., pine) Ovulate cone Pollen cone Fertilization (union of 1 egg and 1 sperm) produces an embryo Megasporangium Microsporangium Seed Seedling Fig. 30.6 Embryos develop within seeds Seeds germinate and embryos become seedlings Megaspore Microsporocyte Pollen Megasporocyte Egg nuclei Sperm nuclei Archegonium

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Fig. 29.7 Bryophytes (nonvascular plants) Seedless vascular plants Seed plants Vascular plants Land plants Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Charophyceans Liverworts Hornworts Mosses Lycophytes (club mosses etc.) Pterophyte (ferns, horsetails, whisk fern) Gymnosperms Angiosperms Hashed lines indicate uncertainties Plant Origins Seed plants appeared ~360 m.y.a. with the rise of the Gymnosperms Flowering plants (Angiosperms) – the other surviving lineage – appeared ~200 million years later

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Flowering plants; seeds develop inside sporophyte ovaries Angiosperms

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Amborella trichopoda Water lily Star anise BASAL ANGIOSPERMS HYPOTHETICAL TREE OF FLOWERING PLANTS Amborella Water lilies Star anise Magnoliids Monocots Eudicots Magnolia grandiflora Angiosperms Flowering plants; seeds develop inside sporophyte ovaries ~250,000 extant species 6 main clades (see pg. 602)

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Angiosperms (a.k.a., flowering plants) Fig. 30.7 Petal Sepal Anther Stigma Ovule Ovary Receptacle Style Filament (♀) (♂) Carpel Stamen

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Angiosperms Complete flowers have sepals, petals, stamens & carpels See Fig. 30.7

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Angiosperms See Fig. 30.7 Complete flowers have sepals, petals, stamens & carpels

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Angiosperms See Fig. 30.7 Complete flowers have sepals, petals, stamens & carpels

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Ovules Angiosperms See Fig. 30.7 Complete flowers have sepals, petals, stamens & carpels

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Bisexual flowers have both male (stamens) and female (carpels) reproductive structures; so complete flowers are also bisexual Angiosperms See Fig. 30.7 Complete flowers have sepals, petals, stamens & carpels

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Incomplete flowers lack one or more of the following: sepals, petals, stamens or carpels E.g., most grasses lack petals Angiosperms

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Self-fertilization Angiosperms See Fig. 30.7 Some bisexual flowers can self-fertilize

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Monoecious individuals have separate male and female unisexual flowers on the same plant; which helps reduce self-fertilization, but does not eliminate it Incomplete, staminate flowers lack carpels Incomplete, carpellate flowers lack stamens E.g., squash Angiosperms

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Dioecious species have separate male and female individuals; which eliminates the possibility of self-fertilization E.g., branches from two holly plants Staminate flowers Carpellate flowers Angiosperms

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Angiosperms Monocots Eudicots 1 cotyledon 2 cotyledons Parallel veins Netlike veins Scattered vascular tissue Ring of v. tissue Fibrous roots Tap root 1 opening in pollen 3 openings in pollen Floral organs in 3s Floral organs in 4s or 5s See Fig. 30.12

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Angiosperms Meiosis Fertilization Key Haploid Diploid Sporophyte Gametophytes Fig. 30.10 Meiosis Anthers contain microsporangia that produce microspores Each microspore forms a pollen grain (a male gametophyte) Ovules contain megasporangia that produce megaspores Each megaspore forms an embryo sac (a female gametophyte) Microspore Megaspore Pollen Embryo sac Microsporangium Megasporangium

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Angiosperms Meiosis Fertilization Key Haploid Diploid Sporophyte Gametophytes Fig. 30.10 Meiosis Microspore Megaspore Pollen Embryo sac Microsporangium Megasporangium Zygote Embryo Seedling Egg 2 sperm Pollen disperses to stigmas Double fertilization is unique to angiosperms From a single pollen grain, one sperm unites with the egg to produce a zygote; the second sperm unites with 2 nuclei of the embryo sac to produce triploid (3n) endosperm Endosperm Sperm enter an ovule through a micropyle

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Some key points to remember: All spores and gametes are haploid Sporophytes are diploid, and produce spores Gametophytes are haploid, and produce gametes Sporophyte (2n) (If heterosporous: separate mega & microsporangia and two types of spores; if homosporous: single type of sporangia and single type of spore) Gametophyte (1n) (If bryophyte, seedless vascular or gymnosperm, archegonia & antheridia present) Spores (1n) Gametes (1n) meiosis mitosis

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Seed plants and human welfare Humans began practicing agriculture only about 18,000 years ago Multiple independent origins

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Seed plants and human welfare Just 6 crops – wheat, rice, maize (corn), potatoes, cassava (manioc), sweet potatoes – yield 80% of all the calories consumed by humans Even so, most of our food currently comes from angiosperms

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Seed plants and human welfare It takes ~5 pounds of grain to produce 1 pound of grain-fed beef