Plant Diversity II The Evolution of Seed Plants

1. Plant Diversity IIThe Evolution of Seed Plants Chapter 30

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

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

4. Seedless vascularplants Sporophyte dominant; sporophyte initially dependent; gametophyte independent Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Fig. 30.2

5. Seedless vascularplants Sporophyte dominant; sporophyte initially dependent; gametophyte independent Bryophytes Gametophyte dominant; sporophyte dependent; gametophyte independent Seed plants Sporophyte dominant; sporophyte independent; gametophyte dependent & microscopic GymnospermsGametophytes develop inside cones AngiospermsGametophytes develop inside flowers Fig. 30.2

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

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

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

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

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

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

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

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

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

15. Gymnosperms Phylum Gnetophyta 3 genera: Gnetum

16. Gymnosperms Phylum Gnetophyta 3 genera: Gnetum Ephedra

17. Gymnosperms Phylum Gnetophyta 3 genera: Gnetum Ephedra Welwitschia

18. Gymnosperms Phylum Coniferophyta E.g., longleaf pine

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

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

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

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

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

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

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

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

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

28. Angiosperms Flowering plants;seeds develop inside sporophyte ovaries

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

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

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

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

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

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

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

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

37. Angiosperms Self-fertilization Some bisexual flowerscan self-fertilize See Fig. 30.7

38. Angiosperms 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

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

40. Angiosperms Monocots Eudicots 2 cotyledons 1 cotyledon Netlikeveins Parallelveins Ring of v. tissue Scatteredvascular tissue Tap root Fibrous roots 3 openingsin pollen 1 openingin pollen Floral organsin 4s or 5s Floral organs in 3s See Fig. 30.12

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

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

43. 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) meiosis Spores (1n) Gametes (1n) Gametophyte (1n) (If bryophyte, seedless vascular or gymnosperm, archegonia & antheridia present) mitosis

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

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

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