Biological Foundations 112, Lecture 30


Pterophyta

Chapter 27, pages 558-560
Basic Botany-3 9:52-18:58
Five Kingdoms-5 3:53-12:24


I.   Characteristics

     A.   Habitat

            1.   Shade-loving

            2.   Damp areas

            3.   Few xerophytic species

            4.   From tropics to the poles but mostly tropical

     B.   Sporophyte plant and gametophyte plant grow separately

     C.   Most species are homosporous, a few species are heterosporous

     D.   Structure

            1.   Branched rhizome

            2.   Roots adventitious from the rhizome

            3.   Leaves (true leaves) are megaphyllous (more than one vein in the leaf)

II.  Family Polypodiaceae as an example

     A.   Mature sporophyte generation

            1.   Dominant generation of the life cycle

            2.   Leaves

                  a.   Megaphyllous

                  b.   Called fronds

                  c.   Differ from angiosperm leaves by having:

                        (1)  Apical meristem at the tip of the leaf that is never differentiated

                               (a)  Leaves unroll as they mature

                               (b)  Apical meristem continues to produce more leaf cells

                               (c)  Some species have leaves 100 feet long

                               (d)  Thus, some species have active meristem for many years

                        (2)  Spores borne on the lower surface of the leaves

                  d.   Leaves are mostly compound, some have simple leaves

                  e.   Rachis - the main axis of the usually pinnately compound leaf

            3.   Vascular system of the rhizome

                  a.   Several vascular bundles embedded in a "pithy" cortex region

                  b.   Xylem in the center of the vascular bundle which for most species is tracheids

                  c.   Phloem surrounds xylem

                  d.   Pericycle surrounds phloem

                  e.   Endodermis surrounds pericycle

                  f.    Fibers and parenchyma make up the cortex

                  g.   The cortex is surrounded by the epidermis

            4.   Reproduction

                  a.   Asexual reproduction

                        (1)  Fragmentation by death of a portion of the rhizome produces two plants

                        (2)  Deciduous leaf borne buds grow into new plants - only in a few genera

                  b.   Sexual reproduction

                        (1)  Fronds may be fertile or sterile

                        (2)  Sterile fronds feed the rhizome and do not produce spores

                        (3)  Fertile fronds produce spores

                        (4)  Sporangia cover the leaf in several ways depending upon species:

                               (a)  Cover the entire lower leaf surface

                               (b)  Grouped in sori (clusters) near the veins

                               (c)  Clustered only along the margins of the leaf

                        (5)  Structure of the sporangia

                               (a)  One layer of epidermal cells that are very thin and transparent

                               (b)  Annulus - a band of thick-walled cells surrounding the sporangium

                                     i)   The annulus is part of the epidermal cells

                                     ii)   Aids in opening of the sporangium and the release of spores

                               (c)  The center (inside the epidermis) is filled with spore mother cells

                                     i)    Each spore mother cell divides by meiosis to form four spores

                                     ii)   Spores are homosporous

                        (6)  Coverings over the clusters of sporangia

                               (a)  Indusium - umbrella-like covering over the sorus

                               (b)  False Indusium - rolled over margin of the leaf, containing the marginal
                                                               sporangia

     B.   Mature gametophyte generation

            1.   Gametophyte plant is termed a prothallium

            2.   Small, green, heart-shaped plant (several could fit in your fingernail)

            3.   Matures rapidly and is short-lived

            4.   Rhizoids grow on the lower surface

            5.   Monoecious (antheridia and archegonia form on the same plant)

            6.   Antheridia

                  (a)  Forms when the prothallium is young

                  (b)  Distributed over the lower surface of the prothallium near the tip of the "heart"

                  (c)  32 sperm form in each antheridium

            7.   Archegonia

                  (a)  Formed when the prothallium is older

                  (b)  Distributed over the lower surface of the prothallium near the notch of the "heart"

                  (c)  Neck cells project slightly out of the lower surface

     C.   Fertilization and development

            1.   Sperms are released when sufficient water is available for them to swim in

            2.   Sperms swim to the archegonia by a chemotactic response

            3.   Zygote forms from the union of the egg and sperm

            4.   Zygote divides by mitosis and develops into an embryo

            5.   With continued mitosis the embryo differentiates into a young sporophyte plant

            6.   When the primary root, stem and leaves begin to function, the sporophyte is on its    
                   own and the gametophyte dies

III. Orders of Pterophyta

      A.   Order Ophioglossales

             1.   Called grape ferns

             2.   Clusters of sporangia resemble clusters of grapes

             3.   Sporangia are large and globular without an annulus

             4.   Homosporous

             5.   Uncommon

      B.   Order Filicales

             1.   True ferns

             2.   Sporangia minute with an annulus

             3.   Homosporous

             4.   Common group studied in class and lab

             5.   Family Pteridaceae

                   a.   Pteris

                   b.   Sporangia clustered along the leaf margin with a false indusium

             6.   Family Polypodiaceae

                   a.   Polypodium

                   b.   Sporangia clustered in sori which may or may not have true indusia

      C.   Order Marsileales

             1.   Plants not fern-like

             2.   Plants grow on the mud

             3.   Leaves look like 3-leaved clover leaves

             4.   Sporangia

                   a.   Small, round and bony with no indusium

                   b.   Near base of the leaf stalk

                   c.   Termed sporocarps

             5.   Heterosporous

             6.   Uncommon

      D.   Order Salvineales

             1.   Plants not fern-like

             2.   Plants are aquatic and grow on the surface of stagnant water

             3.   Plants are very small in size

             4.   Sporangia

                   a.   Small, round and bony with no indusium

                   b.   Near base of the leaf stalk

                   c.   Termed sporocarps

             5.   Heterosporous

             6.   Uncommon


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