BOTANY - BIO 2500 -- LECTURE 19 part II
 
 
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Lower Vascular Plants - Ferns and Allies


Part I Homospory    updated Aug. 9, 2003
 
Selaginella Life Cycle Heterospory Evolutionary Trends

Lower Vascular Plants  Kean Lab Help

quiz  Survey   Phylum directory    Table of characteristics - Konig   Key
   Psilophyta, Lycopsida, Sphenopsida   Pterophyta



Selaginella - Hawaii - description and images

Heterospory vs Homospory  Selaginella - life cycle
 
Homospory Heterospory
Most Ferns, Psilophyta,
Sphenophyta, some Lycophyta
Selaginella, a few ferns (Salvinia, Marselia), all *seed plants
one type of spore two types of spores, often large + small 
  Megaspores
  Microspores
one type of sporangium two types of sporangia 
  Megasporangia
  Microsporangia
one kind of gametophyte two types of gametophytes 
  megagametophyte
  microgametophyte
bisexual gametophyte Unisexual gametophyte
   most important distinction
* seed plants are functionally heterosporous (megaspore size may be <, > or = microspore)
  Megaspore size reduced when became permanently retained in sporangium

Microphyll - no leaf gap Microphyll-  no leaf gap
Sporophyll - spore bearing leaf Sporophyll - spore beariang leaf
Megasporophyll Microsporophyll
  Megasporangium   Microsporangium
  Megaspore mother cell   Microspore mother cell
      meiosis       meiosis
 Megaspores
    large 
    thick-walled 
   1-4 per sporangium 
   white to yellow
  Microspores
    smaller 
    thin-walled 
    numerous 
    orange


Selaginella Lycophyta-Selaginellales-1    nice information and images

Classified in Lycophyta    images- U. Wisconsin   more images - U. Wisconsin
 

http://botit.botany.wisc.edu:16080/images/401/
Lycophyta_(Microphyllophyta)/Selaginellaceae/Selaginella/S_apoda_KS.jpg
Most tropical
Often prostrate

4 rows of microphylls
  2 large
  2 small

http://botit.botany.wisc.edu:16080/images/401/
Lycophyta_(Microphyllophyta)/Selaginellaceae/Selaginella/
Dorsal_and_ventral_MC.low.jpg
 


x.s. Selaginella stem
x.s. rhizome and roots


http://www.botany.hawaii.edu/
faculty/webb/BOT201/
Selaginella/LeafCloseUp-3-Lab.jpg


http://botit.botany.wisc.edu:16080/images/401/
Lycophyta_(Microphyllophyta)/Selaginellaceae/Selaginella/LS_strobilus_MC.jpg

http://botit.botany.wisc.edu:16080/images/401/
Lycophyta_(Microphyllophyta)/Selaginellaceae/
Selaginella/Strobilus_With_Lycopodium.jpg

 
 
                  Strobilus
  Cone
l.s.
strobilus


http://botit.botany.wisc.edu:16080/images/
401/Lycophyta_(Microphyllophyta)/
Selaginellaceae/Selaginella/
Prep_slide_Strobilus_ls_MC.low.jpg

                        Sporophylls
Microsporophyll Megasporophyll

http://home.uleth.ca/
bio/bio1020/images/sel4b6.jpg


gopher:

http://botit.botany.wisc.edu/images/130/Fern_Allies/
Lycophyta/Selaginella/Mega_micro_MC.low.jpg

http://botit.botany.wisc.edu/images/130/Fern_Allies/Lycophyta/
Selaginella/Strobilus_10x_MC.jpg

http://www.biologie.uni-hamburg.de/b-online/vascular/images/sel_sp_cu.jpg
link to descriptions

http://www.biologie.uni-hamburg.de/b-online/vascular/images/sel_def.jpg
Selaginella - link to life cycle and images
                Spores and Gametophytes
Microspore and Microgametophyte Megaspore and Megagametophyte



http://botit.botany.wisc.edu:16080/images/401/
Lycophyta_(Microphyllophyta)/Selaginellaceae/Selaginella/
Megaspore_&_Microspores_MC.jpg
Spore wall
Megagametophyte
Sporophyte

Megagametophyte

Gametophyte Development
http://www.botany.hawaii.edu/
faculty/webb/BOT201/
Selaginella/
Megagametophyte240Lab.jpg

.
http://www.botany.hawaii.edu/
faculty/webb/BOT201/
Selaginella/ArchClose400Lab.jpg


http://www.botany.hawaii.edu/
faculty/webb/BOT201/Selaginella/
GametoSporo240Lab.jpg

http://home.uleth.ca/bio/
bio1020/images/sel6b6.jpg
Life cycle
.
Life cycle - do it yourself



Selaginella and heterospory  - link to seed plants

.
Life Cycle of Selaginella


.
Evolutionary Trends

  Points of special note (for evolution toward land plants)

  • 1. Gametophytes retained within spore wall - -  endosporic
  • independent of external water for growth and development
  • independent of photosynthesis for most or all growth and development
  • 2. Gametophytes reduced anddependent on nutrients of spore
  • only antheridium + 1 prothallial cell
  • spore provides all nourishment
  • rhizoids only to hold water for fertilization
  • 3. Gametophytes unisexual
  • micro (male) - antheridium
  • mega (female) - archegonia
  • 4. Less dependence on free water for fertilization
  • sperm delivered via air in microspore "pollen-like"
  • microgametophyte independent of water
  • for growth and development
  • for most of gamete transport
  • 5. Role of gametophyte reduced to protection and nutrition of embryo
  • 6. Protection and nutrition of embryo
  • early development of sporophyte within protective megaspore (may still be on sporophyll)
  • food for embryo guaranteed; prepackaged by parent sporophyte in megaspore



  • Preface to Seed Plant  - trends that will continue

    Greater adaptation to terrestrial life

    Increased protection of sporangia by parent sporophyte tissue

  • within integument of ovule in gymnosperms
  • within integuments of ovule and wall of carpel in angiosperms

  •  

     
     
     

    Compare position in Psilotum with Lycopodium / Equisetum / indusiate fern

    Increased protection of meiospores
  • Megaspores retained (limited in Selaginella)
  • Reduction of gametophytes
  • Size decreases
  • Independent --> Dependent
  • Vegetative cells reduced, essentially lost
  • Sterile jacket reduced or lost
  • Increased protection (enclosed)
  • Megagametophyte retained
  • Microgametophyte released (resistant spore wall, pollen tube, etc.)
  • Compare fern prothallus with gametophytes of Selaginella
    Free water not needed for fertilization
      Free swimming sperm --> pollen tube + flagellated sperm  --> pollen tube + sperm nuclei
    .
    Nutrition of embryo
         More reliable food source
         megaspore --> megagametophyte  --> endosperm
    .
    Resting stage
         spore  --> seed
     



     


     




     
     
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    BOTANY - BIO 2500 -- LECTURE 19 part II local

         Principles of Botany
              Bio. 2500