Mosses and Ferns

1. Mosses and Ferns

2. Evolutionary developments necessary for plants to colonize land Stage One: Becoming multicellular Occurred in water Enables specialized tissues to develop Stage Two: Developing sporangia Enables dispersal on land Stage Three: Developing a large sporophyte Confers competitive advantage Provides perennial spore production Stage Four: Removing dependence of fertilization on a film of water Enables survival in dry environments

3. History of evolution of major plant types on land

4. Stage One of adaptation to living on land Land plants required several adaptations to be successful that require multi-cellular tissues: The land that plants colonized was hostile to life. Soil development was minimal. mechanical strength for support, exposed light catching surfaces, anchoring system, conducting system for water, system for obtaining mineral nutrients, a way to restrict water loss in desiccating air, a means of reproducing and dispersing on land

5. Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, 370-380 million years ago. Asteroxylon MAIN FEATURES Simple dichotomous branching Sporangia !5 to 30 cm tall No roots Stomata with guard cells Most had a central vascular strand Cuticle Asteroxylon had leaves –without a vascular connection Devonian plant community

6. Plants living in water release spores and gametes that swim and may be helped to dispersed by water movement Dispersal was solved first – through production of sporangia. The important feature of sporangia is that they lift spores above the ground so they can be dispersed by the wind To live on land plants faced two challenges for their reproduction: 1.Dispersal 2. Fertilization angeion is Latin for case So a sporangia is asporecase

7. Meiosis in the sporangium producing haploid spores. Retention of the zygote by the female gametophyte Delayed meiosis and growth of the sporophyte by mitosis 1.Dispersal Developing sporophyte Zygote Gametophyte Archegonium Stage Two: Developing sporangia Mosses

8. Eight Terms to Learn to understand Alternation of Generations of Land Plants Spores– haploid, single cells produced by meiosis The word “phyte” is Greek for plant Gametes– collective term for sperm and egg Gametophyte– haploid plant that develops from a spore and produces gametes by mitosis Gametangium– a “case” holding gametes Archegonium– flask–shaped container holding the egg cell.(Ancientgonad) The female gametangium. Antheridium– The male gametangium Sporophyte– diploid plant that grows from the zygote and produces spores by meiosis Sporangium– the “case” holding spores

9. Moss life cycle Fig. 25.4, p. 406 Mature sporophyte (spore-producing structure and stalk), still dependent on gametophyte. zygote rhizoid Zygote grows, develops into a sporophyte while still attached to gametophyte. Diploid Stage Meiosis Fertiliztion Haploid Stage Spores form by way of meiosis and are released. Sperm reach eggs by moving through rain drops or film of water on the plant surface. Spores germinate. Some grow and develop into male gametophytes. sperm-producing structure at shoot tip of male gametophyte. egg-producing structure at shoot tip of female gametophyte. Other germinating spores grow and develop into female gametophytes.

10. Moss sporophyte Top of capsule

11. Developing protonema

12. Moss antheridium and archegonium

13. Important life cycle features of mosses Mitosis Spores n Gametes (?) HAPLOID Meiosis Fusion (syngamy) DIPLOID Zygote 2n Mitosis Development of gametophyte thallus Female gamete remains attached to the haploid thallus Development of sporophyte thallus – remains attached to gametophyte

14. Dessication tolerance in Tortula ruralis RAPID WATER LOSS Constitutive Cellular Protection Induction of Recovery and Repair Mechanisms Hydrated Dry Rehydrated Hormone ?

15. Spagnum – the bog-forming species The species forms clumps- minimizing surface area to volume ratio. Unique leaf cells (hyaline cells) of Spahgnum species enable the plant to absorb up to 20 times its own dry weight of water. Fig. 25.5, p. 407

16. How can we characterize mosses?

17. Large size enables competition as well as effective spore dispersal. The perennial root stock enables continued frond and spore production from year to year Sporophyte originally grows from a gametophyte and then develops roots, rhizome, and fronds Fronds growing from a rhizome Ferns Stage Three: Developing a large sporophyte In ferns the sporophyte is only dependent on the gametophyte for obtaining nutrient, water, and physical support when it is first formed.

19. Fern life cycle The sporophyte (still attached to the gametophyte) grows, develops. sorus (one of the spore-producing structures) zygote Diploid Stage fertilization meiosis Haploid Stage egg-producing structure Spores develop. Spores are released mature gametophyte (underside) Archegonia egg sperm-producing structure Spore germinates, grows into a gametophyte. sperm Antheridia

20. Sporangia http://departments.bloomu.edu/biology/chamuris/concepts2/labimg.html Polypodium spp sori sporangia A sorus

21. Magnified sporangia Polypodium spp Sporangia Developing spores

22. Polypodium spp Gametophyte Developing sporophyte Gametophyte

23. Arrangement of sporangia on two ferns In lines on a broadleaved type At the end of the leaves Adiantum Asplenium

24. Tree ferns Cibotium menziesiiin habitat in Hawaii.  Photo courtesy of Peter Richardson. Cyathea australis with the uncurling croziers visible.  Photo courtesy of Scott Ridges Conducting tissue

25. How can we characterize ferns?

26. Coal formation Jungle-like forests of the Carboniferous were dominated by giant ancestors of club mosses, horsetails, ferns, conifers, and cycads. Most of the plant fossils found in the coals and associated sedimentary rocks show no annual growth rings, suggesting rapid growth rates and lack of seasonal variation in the climate (tropical). Anaerobic conditions and periodic inundations of the sea

27. Early Carboniferous Equator Appalachians Britain Ice cap

28. Equator Appalachians Britain Ice cap