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Vascular Plants. Generalized life cycle Moss life cycle.

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Presentation on theme: "Vascular Plants. Generalized life cycle Moss life cycle."— Presentation transcript:

1 Vascular Plants

2 Generalized life cycle

3 Moss life cycle

4 Spore -> Gametophyte

5 Gametophyte -> Zygote

6 Zygote -> mature sporophyte

7 Sporophyte -> spores

8 Vascular Plants

9 Branching sporophyte in Silurian First vascular plants in Devonian Liverwort spore tetrads - end of Ordovician First fossil of non-algal land plant in Silurian mya First flowering plants Age of Ferns

10 Fossils Probable embryophyte spores at 450 Ma Cooksonia fossils in Silurian (ca. 430 Ma)

11 Plants like Cooksonia lacked a vascular system Dichotomously-branching axes Terminal sporangia No roots or leaves

12 Over-time became larger, more complex, and acquired a vascular system Time

13 Living vascular plants (Tracheophytes) Stems and roots (often leaves)

14 Living vascular plants (Tracheophytes) Stems and roots Sporophytes dominate the life-cycle

15 Tree fern Sporophyte dominance Gametphyte

16 Why sporophyte dominance? Spore dispersal by wind: aided by height Competition for light (gametophyte constrained by the need for water)

17 Living vascular plants (Tracheophytes) Stems and roots Sporophytes dominate the life-cycle A vascular (transport) system

18 Vascular system Xylem (water transport) and phloem (metabolite transport) XylemPhloem Stem Root Vascular Bundle

19 Xylem Composed primarily of Tracheids Elongated, dead, cells Cell wall impregnated with lignin Transport of water from soil to leaves

20 Phloem Transport via sieve elementsTransport via sieve elements Elongated, living cellsElongated, living cells Transport of sugars, hormones, etc.Transport of sugars, hormones, etc.

21 3 Major groups of Vascular plants Seed plants (gymnosperms and angiosperms) Lycophytes (club mosses and their relatives) Moniliforms (ferns and fern allies)

22 Major tracheophyte taxa Seed Plants (ca. 290,000 species) Lycophytes (ca. 1,100 species) Ferns and allies (ca. 11,000 species) Tracheophytes that are not seed plants are sometimes called “pteridophytes”

23 Vascular plant phylogeny bryophytes Cooksonia lycophytesFerns +Seed plants Branched sporophyte Vascular tissue, Roots Megaphylls Microphylls

24 Organ systems origins Stems - dichotomous branching

25 Organ systems origins Stems Leaves –Microphylls

26 Organ systems origins Stems Leaves –Microphylls –Megaphylls

27 Organ systems origins Stems Leaves –Microphylls –Megaphylls Roots

28 Homospory versus Heterospory

29 An important variation: Heterospory Selaginella (heterosporous) Megasporangium Microsporangium Lycopodium (homosporous)


31 Heterospory Microspores and megaspores produced in different sporangia on different leaves (microsporophylls; megasporophylls) Microspores grow into male gametophytes Megaspores grow into female gametophytes - remains within spore wall

32 Haploid Diploid Homospory gametophyte sperm egg zygote sporophyte spore

33 Haploid Diploid Heterospory female gametophyte sperm egg zygote sporophyte megaspore microspore male gametophyte

34 Heterospory evolved many times. Why? Increases potential for outcrossing Specialization of function between micro- and megagametophyte permits greater efficiency (less cost)

35 3 Major groups of Vascular plants Seed plants (gymnosperms and angiosperms) Lycophytes (club mosses and their relatives) Moniliforms (ferns and fern allies)

36 Moniliforms Spermatophyta Lycophyta Pryer et al. 2001

37 Lycophytes 380 Ma old 1100 spp. Microphylls only Sister group to the other living vascular plants

38 Lycophytes 380 Ma old 1100 spp. Microphylls only lycophytesFerns +Seed plants Megaphylls Microphylls

39 Lycophytes Lycopodium Selaginella Isoetes Selaginella Clubmoss (Lycopodium)

40 Lepidodendron Sigillaria Carboniferous lycopods up to 40 m

41 Lycopodium life cycle I Sporophyte makes sporangia often in a “strobilus” Sporangium

42 Lycopodium life cycle I Sporophyte makes sporangia often in a “strobilus” Sporophyll Sporangium

43 Lycopodium life cycle II Spores dispersed by wind: germinate into a minute gametophyte Spore Thallus Rhizoids Spore

44 Lycopodium life cycle III Gametophyte produces archegonia and antheridia (bisexual) Biflagellate sperm fertilize egg cells New sporophyte grows Archegonial neck

45 Lycophyte diversity 3 Major groups –Lycopodiaceae (club mosses) –Selaginella –Isoetes

46 Lycopiaceae Approximately 400 species Dominated Carboniferous, up to 40 m tall –form much of modern coal Homosporous Archegonia and Antheridia can take 6-15 years to mature

47 Selaginella Approximately 700 extant species Heterosporous Moist habitats or "resurrect" Selaginella umbrosa

48 Isoetes Approximately 200 species Grow in water or dried pools

49 Moniliforms Spermatophyta Lycophyta

50 Ferns and fern allies (moniliforms) Includes ferns (Pterophyta) and two small groups (Psilophyta and Sphenophyta) ca. 12,000 spp. Homosporous or heterosporous Megaphylls (lost in Psilophyta and Sphenophyta) Ecologically important especially as tropical epiphytes

51 Moniliforms Ferns and Fern Allies

52 Psilotum Equisetum

53 Ferns and Fern Allies eusporangiate ferns Sporangium wall has 2 or more cell layers

54 Ferns and Fern Allies leptosporangiate ferns Sporangium wall has 1 cell layer

55 Ferns and Fern Allies Psilotum and Ophioglossum

56 Psilotaceae/Psilophyta Psilotum (2 spp.) and Tmesipteris (15 spp.) No roots and reduced or absent leaves, photosynthetic stems Sporangia on lateral branches Homosporous Thought to be "primitive vascular plants", but more likely simplified due to association with fungi.

57 Psilotaceae Sporangium Reduced forked leaves Tmesipteris Psilotum

58 Dichotomizing stem, no rootsLong-lived gametophytes

59 Ophioglossaceae Adder's tongue, eusporangiate ferns Homosporous Worldwide, common in disturbed areas Botrychium (~60 spp.) and Ophioglossum (30 spp.) Ophioglossum can have upwards of 1400 chromosomes - perhaps more then any other organism

60 Ophioglossaceae Sterile blade spore bearing sporophore

61 Ophioglossaceae Botrychium virginianum

62 Ferns and Fern Allies Equisetum

63 Equisetaceae Horse tails Equisetum (15 spp.) Homosporous Dates back to Devonian, with 20 m high stems - lots of diversity in Carboniferous forests Extant species "living fossils" Leaves whorled, fused into sheaths at base, only microphylls

64 Equisetum

65 Calamites (Carboniferous) Extinct trees Calamites


67 Equisetum gametophyte (hermaphroditic)

68 leptosporangiate ferns

69 Osmunda Most ferns species are Leptosporangiate Ferns Large megaphylls (fronds) unfold lengthwise from a "fiddlehead"

70 Section through sorus Sporangium Sporangia are arranged in sori SporangiaIndusium Sori

71 Fern gametophyte (prothallus)



74 Ferns Walking fern Epiphytic fern (Platycerium) Maidenhair fern Tree ferns (Cyatheaceae)

75 Leptosporangiate ferns App. 11,000 species in recognized groups (most of fern diversity) Cover 4 of the major clades - Marsileaceae - Osmundaceae - Cyatheaceae - Polypodiaceae

76 Marsileaceae Salvinia Marsilea Mostly aquatic Leave blade divided into 2-4 leaflets (clover-like) Heterosporous - megagametophytes with only one archegonium Symbiotic with cyanobacteria, fertilized rice fields Spores remain viable for a century

77 Osmundaceae Sporangia loose, not in sori Homosporous Osmunda Leptopteris Todea

78 Cyatheaceae Tree fern growth Sporangia in sori on bottom of leaf Stem usually single and erect Alsophila Cyathea

79 Polypodiaceae Asplenium Adiantum Pteris Polypodium Tectaria Nephrolepis Elaphoglossum

80 Main points Features of vascular plants Homospory versus heterospory Megaphylls vs. microphylls Life cycle of the fern Fern allies: Psilotum, Equisetum

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