Mosses and Ferns

Stage One: Becoming multicellular Stage Two: Developing sporangia Occurred in water Enables specialized tissues to develop 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 Evolutionary developments necessary for plants to colonize land

History of evolution of major plant types on land

Stage One of adaptation to living on land The land that plants colonized was hostile to life. Land plants required several adaptations to be successful that require multi-cellular tissues : 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 Soil development was minimal.

Devonian plant community Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, million years ago. Simple dichotomous branching MAIN FEATURES !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 Sporangia Asteroxylon

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

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

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

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

Moss sporophyte Top of capsule

Developing protonema

Moss antheridium and archegonium

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

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

Fig. 25.5, p. 407 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. Spagnum – the bog-forming species

1.Plants accumulate matter and make growth 2.Plant growth is an organized process following rules of anatomy and morphology 3.Plants maintain their heat and water balance 4.Plants have a life cycle with reproduction and dispersal 5.Evolution is a constant process How can we characterize mosses?

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. 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 Ferns Fronds growing from a rhizome

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

Sporangia Polypodium spp sori sporangia A sorus

Magnified sporangiaMagnified sporangia Polypodium spp Sporangia Developing spores

Gametophyte Polypodium spp Gametophyte Developing sporophyte

Arrangement of sporangia on two ferns In lines on a broadleaved typeAt the end of the leaves Adiantum Asplenium

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

1.Plants accumulate matter and make growth 2.Plant growth is an organized process following rules of anatomy and morphology 3.Plants maintain their heat and water balance 4.Plants have a life cycle with reproduction and dispersal 5.Evolution is a constant process How can we characterize ferns?

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). Coal formation Anaerobic conditions and periodic inundations of the sea

Early Carboniferous Britain Ice cap Equator Appalachians

Britain Ice cap Equator Appalachians