BIO 131
Lecture Notes
Nov. 6, 2008 

In addition to the other characteristics of Kingdom Plantae, vascular plants have the following characteristics.
Sporophyte (2n) is the dominant phase of life history
Well-developed vascular (conducting) system - xylem & phloem
        320,000+ species on Earth today
        the most successful and ecologically dominant plants on land

Two kinds of vascular plants

       vascular cryptogams
                [crypto- = hidden; gams = reproductive structures
                = vascular plants that do not form seeds

        phanerogams
                = seed plants

Oldest vascular plant fossils are about 4.2 x 10⁸ yrs old (see Fig. 17-1, p. 369 in textbook)
In other words, it took about 30 million years for plants to develop xylem and phloem after they first colonized land.

Endomycorrhizal relationship was probably a prerequisite for land colonization
            The gametophytes of many vascular cryptogams  are mycorrhizal.

             Fossils of the earliest vascular plants have endomycorrhizae.

            The roots of most seed plants are mycorrhizal

Adequate ozone layer must have been established before plants could adapt to terrestrial environments

EARLIEST VASCULAR PLANTS:
       sporophyte phase is the dominant phase of life cycle (see Fig. 17-8, textbook)
       lacked roots as we know them (had only rhizoids and mycorrhizae)
        were dichotomously branched  
        had microphylls only (megaphylls developed later, from telomes) - see Fig. 17-7, p. 373 in textbook
                Megaphylls have leaf gaps at the nodes and microphylls do not.

      All vascular plant sporophytes have sporophylls. Sometimes the sporophylls are microsphylls, and
      sometimes they are megasporophylls. Also, there are microsporophylls and megasporophylls to consider.
      Is this confusing??

      Then, follow this link to find out more about PHYLLS.

VASCULAR PLANT ADAPTATIONS FOR TERRESTRIAL LIVING
These adaptations are mainly related to (1) relatively limited water supply on land, and (2) higher light intensity and opportunity for increased photosynthesis on land.

       Cuticle
                water conservation

       Periderm
                water conservation

       Stomata
                water conservation
                permit efficient gas exchange

       Vascular tissue
                efficiency in getting and transporting water
                permit more extensive tissue systems --> more photosynthetic surface
                provide better spore dispersal (sporangia above ground disperse their spores better)

       Leaves
                much more efficient photosynthesis than algae
                now, one individual can make many times the amount of food than before land plants existed

Phylum RHYNIOPHYTA    [common name = ] Rhyniophytes         NOW EXTINCT
        earliest known vascular plants
        homosporous
               Homosporous means that all of the spores are about the same size.  (see p. 376)
        microphylls
        >420 - 390 x 10⁶ yrs BP
        Similar to today's Psilophytes (which we will cover next time) 

Phylum ZOSTEROPHYLLOPHYTA  Zosterophyllophytes   NOW EXTINCT
        homosporous
        microphylls
        >408 - 370 x 10⁶ yrs BP
        Probably ancestral to Phylum Lycophyta

Phylum TRIMEROPHYTA       Trimerophytes        NOW EXTINCT
        homosporous
        microphylls
        >395 - 375 x 10⁶ yrs BP
       Probably ancestral to ferns and gymnosperms

  Phylum?? PSILOPHYTA       Psilophytes
        homosporous
        microphylls
        mycorrhizal gametophytes
       sporophyte has no roots (rhizoids only)
        2 small genera resembling Rhyniophyta (Psilotum, Tmesipteris)
        occurrence is pantropical habitats (meaning, worldwide in the tropics)
        (We will see Psilotum (= whisk fern) in lab.)

        NOTE:  The status of this phylum is in question.  Evidence that favors maintaining this phylum 
        are (1) a primitive vascular system (called a protostele, where the xylem is the middle of the stem
        [similar to dicot roots]) identical to the earliest land plant fossils; (2) microphylls; and (3) dichotomous
        branching (similar to earliest land plant fossils).  Evidence against maintaining this small group as a
        separate phylum includes (1) complex 3-parted sporangia, indicating evolutionary reduction from a
        more complex sporophyte, and (2) evidence from molecular genetics that shows a genetic relationship
        to ferns.

Phylum LYCOPHYTA        Lycopods
        homosporous or heterosporous
        microphylls
        sporophyte has true roots
        mycorrhizal gametophytes
        this group has been on Earth continually for about 400 x  10⁶ yrs
       very dominant during Carboniferous Period (360-286 x 10⁶ yrs BP) - many were trees then
                source of many coal deposits  
       today, there are only about 1000 species 
       several genera are native in Kentucky, including Lycopodium, Selaginella, Isoëtes

        LIFE CYCLES TO KNOW: Lycopodium (pp. 382-383)     Common name =  CLUBMOSS 
                                                                    homosporous   
                                                              Selaginella (pp. 386-387)    Common name =  SPIKEMOSS
                                                                    heterosporous   
                                                                    we will examine these life histories in class on Nov. 10

end of notes for Nov. 6