Biological Foundations 112, Lecture 28


Psilophyta and Lycophyta

Chapter 27, pages 555-557
Five Kingdoms-5 3:53-7:51


I.   Introduction to Vascular Plants

     A.   Vascular tissue

            1.   All species contain vascular tissue (xylem and phloem)

            2.   Probably the single most important character for terrestrial habitation

     B.   Fertilization

            1.   Free water is needed for fertilization in Division Psilophyta through Pterophyta

            2.   Pollen is used for fertilization in Division Cycadophyta through Anthophyta

     C.   Sporophyte

            1.   Dominant generation

            2.   Independent of the gametophyte when mature

            3.   Sporophyte is dependent on the gametophyte only in the early embryonic stages

     D.   Gametophyte

            1.   Small and separate in Psilophyta through Pterophyta

            2.   Parasitic on the sporophyte in Cycadophyta through Anthophyta

     E.    Divisions of Vascular Plants

            1.   Division Psilophyta - wisk ferns

            2.   Division Lycophyta - club mosses

            3.   Division Sphenophyta - horsetails

            4.   Division Pterophyta - ferns

            5.   Division Cycadophyta - cycads

            6.   Division Ginkgophyta - ginkgos

            7.   Division Coniferophyta - conifers

            8.   Division Gnetophyta - joint-fir/Mormon tea

            9.   Division Anthophyta - flowering plants

                  a.   Class Monocotyledonae - monocots

                  b.   Class Dicotyledonae - dicots

II.  Division Psilophyta

     A.   Distribution

            1.   Generally rare around the world but abundant where it occurs naturally

            2.   Mostly found in tropical and subtropical areas like Florida and Hawaii

            3.   Two genera with one species in each genus

                  a.   Psilotum

                  b.   Tmesipteris

     B.   Structure of  Psilotum

            1.   No Roots

            2.   Rhizome

                  a.   Dichotomously branched

                  b.   Produces rhizoids

                  c.   Contains mycorrhizal fungus

            3.   Stem

                  a.   Flattened

                  b.   Dichotomously branched

                  c.   Contains chlorophyll

                  d.   Xylem and phloem in a radial arrangement within the vascular bundles

            4.   Leaves

                  a.   Not true leaves

                  b.   Small and scale-like with leaf veins

                  c.   Called enations

            5.   Reproduction

                  a.   Sporophyte

                        (1)  Tetraploid

                        (2)  Sporangia borne in the axils of the enations or terminal on the branch

                        (3)   Homosporous

                               (a)  Only one type of spore produced

                               (b)  When the spore germinates into a gametophyte it produces both    
                                      antheridia and archegonia on the same gametophyte plant

                  b.   Gametophyte

                        (1)  Diploid (2N)

                        (2)  Minute and subterranean

                        (3)  Mycorrhizae associated with the gametophyte

                        (4)  Antheridia superficially embedded

                        (5)  Archegonia deeply embedded with only the upper neck cells protruding

                  c.   Fertilization

                        (1)  When free water is available, the sperm are released and swim to the          
                               archegonia and fertilize the egg

                        (2)  The sperm finds the egg by a chemotactic response

                        (3)  The resulting zygote grows into an embryo that differentiates into a complete
                               new sporophyte which eventually matures to produce new sporangia

                        (4)  The spore mother cells in the sporangia undergo meiosis producing a tetrad                                      of tetraspores all of which are diploid

                        (5)  These diploid spores are released to germinate into diploid gametophytes    
                               and with the production of antheridia and archegonia the process starts        
                               over again

III. Division Lycophyta

      A.  Characteristics

            1.   900 species in 4 different genera

            2.   Sporophyte

                  a.   Rhizome dichotomously branched

                  b.   Leaves - called microphylls (contain only one vascular bundle)

                  c.   Stems dichotomously branched

            3.   Sporangia

                  a.   On sporophylls - a microphyll with two sporangia on the upper surface near the                                                           base 

                  b.   Sporophylls are clustered together at the tip of the stem to form a strobilus

                  c.   The strobilus is also called a cone

                  d.   Because the strobilus has the appearance of a club, thus the reason for calling    
                        this group of plants club mosses

      B.   Lycopodium 

             1.   Distribution

                   a.   From the tropics to the arctic

                   b.   Mainly tropical and subtropical

                   c.   Restricted to damp and wet habitats

                   d.   Cannot grow in arid conditions

             2.   Structure of the sporophyte

                   a.   Herbaceous

                   b.   Main stem

                         (1)  A rhizome that runs along the surface of the ground or slightly underground

                         (2)  Branches freely

                         (3)  Upright stems up to 8 inches tall

                   c.   Vascular tissue

                         (1)  Strands of xylem and phloem alternate in the vascular bundle

                         (2)  Resembles roots of higher plants

                         (3)  Xylem is composed of tracheids only

                         (4)  Phloem is composed of sieve tubes without companion cells and some        
                               parenchyma

                         (5)  No pith

                   d.   Microphylls spirally arranged

                   e.   Roots are adventitious from the rhizome

             3.   Reproduction in the sporophyte

                   a.   Asexual by bulbils in some of the species

                   b.   Sexual reproduction

                         (1)  Produces strobili with sporangia on each sporophyll

                         (2)  Homosporous - single kind of spore that produces monoecious                  
                                                         gametophytes

             4.   Reproduction in the gametophyte

                   a.   Spores germinate and grow into a gametophyte (prothallus)

                   b.   Grows on the surface of the ground

                   c.   Has an associated mycorrhizal fungus

                   d.   Quite small gametophyte

                   e.   Antheridia and archegonia produced at different times on the gametophyte to    
                         prevent self-fertilization

             5.   Fertilization and development

                   a.   The antheridia release their sperm when there is enough water for the sperm to  
                         swim in

                   b.   The sperm finds the egg by a chemotactic response

                   c.   Zygote develops into an embryo and finally differentiates into a complete new    
                         sporophyte

      C.   Selaginella

             1.   Distribution

                   a.   Arctic to the tropics

                   b.   Mostly tropical

                   c.   Few in temperate regions

                   d.   Some species xerophytic (resurrection plant, a good example)

             2.   Structure of the sporophyte that are different from Lycopodium

                   a.   Vessels are found in the xylem of some of the species of Selaginella

                   b.   Rhizophores

                         (1)  Leafless branches

                         (2)  Produce adventitious roots at the tip when the tip makes contact with the                                           ground

                   c.   Microphylls four-ranked (four columns along the length of the stem)

                   d.   Sporangia

                         (1)  Heterosporous

                         (2)  Microspores develop into male gametophytes that produce only            
                                antheridia

                         (3)  Microspores develop on microsporophylls within microsporangia

                         (4)  Megaspores develop into female gametophytes that produce only        
                               archegonia

                         (5)  Megaspores develop on megasporophylls within megasporangia

                   e.   Gametophyte

                         (1)  Female

                                a.   Megaspore germinates before being shed from the strobilus

                                b.   Produces archegonia

                                c.   Megaspores can be shed from the strobilus anytime during their            
                                      development

                                d.   Some species do not shed the megaspore from the strobilus until the    
                                      new sporophyte is quite well developed

                         (2)  Male - microspores germinate to form antheridia and sperm before being                                                      shed from the strobilus                           

                    f.   Fertilization frequently occurs while both the microspores and megaspores are  
                         attached to the strobilus when sufficient water is present

                    g.   The zygote develops into an embryo and toward a new sporophyte before the  
                          megaspore is shed from the strobilus

                    h.   If the embryo doesn't get to the ground soon, it will run out of nourishment and  
                         die


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