1. Bryophytes Chapter 22

2. Bryophytes Nearly 25,000 named species Diverse habitats Relatively inconspicuous Ecologically important –Alter pH –Absorb carbon –Regulate nutrient cycling –Colonize barren areas Create soil Reduce erosion

3. Bryophytes Absorb and hold moisture Intolerant of pollution –Good indicators of air and water quality Interesting physiological adaptations –Some can survive extended periods of desiccation Living representatives of ancient lineages of land plants

4. Bryophytes Retained characteristics of algal ancestors –Nutritionally independent and complex gametophyte –Chlorophyll a and b, carotenoids, xanthophylls –Swimming sperm with two asymmetrically attached flagella –Chloroplasts with conspicuous grana –Cell walls composed of cellulose and pectin

5. Bryophytes Retained characteristics of algal ancestors –Cell division present in charophytes but absent in other green algae

6. Bryophytes Problems associated with life on land –Preventing death from drying out –Dispersing spores through air –Avoiding damage from weather and intense solar radiation

7. Sporophyte Evolution Steps in evolution of multicellular sporophyte –Meiosis must be delayed in zygote –Zygote must undergo mitotic cell divisions to create multicellular body Bryophytes nurture sporophyte by embedding it in tissues of gametophyte –Embryo phase retained in all extant land plants –Embryophyte  name used to describe whole land plant group

8. Sporophyte Evolution Value of first sporophytes which were nurtured by gametophyte –Protected spores from desiccation –Allowed bryophytes to produce more spores Spores adapted to new environment –Lost flagella –Became coated with weather-resistant wall

9. Gametophyte Evolution Multicellular gametangia surrounding gametes –Another innovation of bryophytes –Sperm cells made in globular or club-shaped sacs called antheridia –Eggs produced singly in vase-shaped gametangia called archegonia –Gametangia protect developing gametes

10. Stomata and Cuticle First appear in bryophytes Crucial adaptations to life on land Found in virtually all vascular plants Controversial as to whether bryophytes have stomata on gametophytes Cuticle –In many bryophytes, cuticle only covers part of plant Reduces dehydration May also protect against ultraviolet radiation, fungal infection

11. Bryophytes Common name applied to three distinct lineages of plants that lack lignified vascular tissue Do not form a monophyletic group because vascular plants are descended from them Three lineages –Hornworts –Liverworts –Mosses

12. Bryophytes Not clear how the three lineages are related to each other and to vascular plants Recent molecular analysis using nucleic acid sequences has revealed hornworts may represent earliest lineage Also suggests mosses and liverworts are closely related

13. Bryophytes Megafossils of bryophytes  rare Bryophyte study supports following hypotheses –Land plants evolved only once from single algal ancestor (charophyte) –First land plants were bryophytes and appeared no later than Ordovician period, about 475 million years ago

14. Bryophytes –Bryophytes form nonmonophyletic group –Each of three living bryophyte lineages (hornworts, liverworts, mosses) is monophyletic

16. Hornworts Relatively simple Gametophytes produce mucilage inside thallus Ventral portion of thallus has pores –Nostoc (cyanobacteria) enter through pores, form symbiotic colonies Nostoc is protected in hornwort gametophyte and fixes atmospheric nitrogen (which the hornwort requires)

17. Hornworts Unique sporophyte –Grows continually from meristem at its base Sporophyte consists of –Foot –Upright sporangium or capsule Epidermis of sporophytes generally lacks chloroplasts but contains stomata Mass of sporocytes below chlorenchyma tissue  undergo meiosis to produce haploid spores

18. Hornworts Sterile tissue in center of sporangium called the columella Spores released when mature capsule tip splits into two valves Meristematic region just above foot adds new cells to base of sporangium so more sporocytes are continually produced If spores reach favorable environment, undergo mitosis, produce new gametophytes

19. Liverworts Approximately 9,000 species Name comes from –Shape which resembles liver –Early belief that the plants could cure diseases of organs they resembled Gametophyte generation is prominent phase of life cycle Usually grow in moist, shady habitats

20. Liverworts Gametophytes produce variety of volatile oils (stored in organelle called an oil body) –Give liverworts a distinctive odor –May help prevent herbivory –Some compounds show promise as antibiotics and antitumor agents Produce simple sporophytes –Stalk called a seta –Capsule splits into four valves and releases all its spores at one time

21. Liverworts –Elaters Thickened cells inside capsules Separate spores and aid in spore dispersal

22. Liverworts Thallose liverworts –About 15% of all liverwort species –Gametophytes grow Y-shaped branches by simple forking at growing tip –Degree of branching depends on growing conditions –Pores on upper epidermis serve same function as stomata

23. Liverworts Thallose liverworts –Lower thallus cells modified for carbohydrate storage –Rhizoids and sheets of cells (scales) project from lower surface Increase surface area in contact with substrate Anchor the thallus

24. Liverworts Thallose liverworts –Example: Marchantia Reproduces asexually by two methods –Fragmentation –Gemmae »Produced in gemmae cups »Mature gemmae scattered away from thallus »Land on suitable environment can develop into gametophyte plant

25. Liverworts Thallose liverworts Sexual reproduction –Antheridiophores »Resemble tiny beach umbrellas »Produce antheridia –Archegoniophores »Resemble tiny palm trees »Produce archegonia –Sporophytes develop under archegoniophores

26. Liverworts Leafy Liverworts –Largest group of liverworts (about 85% of liverwort species) –Common in humid climates –Varied environments –Distinguished from mosses by leaf arrangement –Reproduce asexually by gemmae

27. Liverworts Leafy Liverworts –Sexual reproduction Archegonia grow on short, leafy branches –Always terminal on stems where they occur Antheridia develop in axils of leaves Sporophytes consist of foot, seta, and sporangium

28. Mosses Larger and have wider distributions than liverworts and hornworts Divided into a number of groups –Granite mosses Most prominent; grow on rocks in cool climates –Peat mosses Mainly grow in acidic bogs –“True” or typical mosses Widest habitat range and most species

29. Mosses Moss life cycle Example: Mnium –Gametophyte has three growth phases Spore germinates to form branching, filamentous structure called a protonema Buds form on protonema Buds grow into upright, branching axes, with small, spirally arranged leaves and rhizoids

30. Mosses Moss life cycle –Each protonema can produce many identical leafy gametophytes –As leafy gametophyte grows, cells in stems differentiate, mature into specialized tissues Epidermal layer surrounding cortex of parenchyma tissue Some species may have thin cuticle over parts of epidermis No stomata

31. Mosses Stem anatomy –May have central strand of conducting tissue Could be made up of hydroids –Thin-walled, dead cells that conduct water –Resemble vessels but lack pitting and lignified walls Some have cells called leptoids –Resemble sieve cells of vascular plants –Surround hydroids –Living, but nuclei degenerate –Parenchyma cells may assist leptoids (like companion cells)

32. Mosses Asexual reproduction –Several methods Protonema may continue to produce new buds Leaf tissue placed in wet soil may produce protonemal strands Rhizoids sometimes produce buds Gemmae may form on rhizoids, leaves, ends of special stalks, or in gemmae cups

33. Mosses Sexual reproduction –Gametangia produced at gametophyte stem tips Gametangia often separated and held upright by sterile filaments called paraphyses –Antheridia Release mature sperm when free water is present

34. Mosses Sexual reproduction –Archegonium Has long neck Thickened venter region surrounds single egg Neck opens creating canal when egg is mature Egg emits chemical attractant Sperm swim down canal toward egg Sperm fertilizes egg creating diploid zygote

35. Mosses Sexual reproduction –Zygote develops into embryo that differentiates into Foot –Penetrates through venter and into gametophyte stem Seta –Elongates and raises yet-to-be-formed sporangium above top of gametophyte Sporangium –Calyptra (protective covering for sporangium) »Necessary for normal growth and differentiation of sporophyte

36. Mosses Sexual reproduction –Sporophyte usually contains chlorenchyma and stomata (allows photosynthesis) –Cells inside capsule undergo meiosis, for spores Granite moss capsules open by slits Peat moss capsules violently eject spores when dried capsule lids blow off

37. Mosses Sexual reproduction True mosses –Mature capsule forms lid (operculum) –Peristome teeth form below operculum »Sensitive to atmospheric humidity »When air is dry, peristome teeth lift out some of the spores

39. Mosses Economic and ecological value –Sphagnum Most economically important bryophyte Superior water-holding capacity Used as wound dressing during World War I –Acidic, sterile tissue acts as antiseptic and an absorbent Peat –Can be cut in blocks, dried, and burned as fuel for cooking and heating

40. Bryophytes Economic and ecological value –Important colonizers of bare rock and sand –May harbor symbiotic nitrogen-fixing cyanobacteria –In tundra, make up as much as 50% of aboveground biomass Important component of food chain in ecosystem

41. Mosses Economic and ecological value –Excellent experimental plants (especially mosses) Easy to propagate Grow in small spaces Easy to clone into sexually identical replicates Easy to observe for growth and developmental changes