Plant Life Cycles

Douglas P. Jensen djensen at HOLLINS.EDU
Mon Oct 13 13:13:13 EST 1997


        This post is rather long-winded--sorry.  

        David Kramer's post brings up one of my pet peeves in plant life
cycles.  Text books generally discuss zygotic, sporic, and gametic
LIFECYCLES, but they are quite confusing and often not well presented. I
think a better way to think of these terms and present them is as types of
MEIOSIS, each related to a specific type of life cycle.   
        Phycologists, who generally work with a greater diversity of
lifecycles than the rest of us, often use a different set of terms.
Haplobiontic refers to plants (if algae really are plants...) that have one
vegetative phase in the life cycle (either 1n or 2n).  Diplobiontic refers
to those with 2 phases (=alt. of generations).  
        An even better set of terms that I learned from a phycologist as a
grad student are haplontic, diplontic, and haplo-diplontic.  These refer to
life cycles with 1n, 2n, or 1n+2n vegetative phases, respectively.
Unfortunately, I cannot find a reference now, so I'm not certain of the
spelling (extra syllables, etc).  In any event, I consider these the best
set of terms.          From these, we can teach students that the important
point is what phase precedes or follows meiosis and teach the 'textbook
terms' as types of meiosis (e.g. zygote undergoes meiosis:  zygotic meiosis,
etc).   Teaching the 'textbook terms' on their own, I find that many
students mistakenly think:  'zygotes are 2n, so zygotic life cycles must
have a dominant 2n stage.'
        Because of the overabundance of terminology in biology and because
the book I use has sporic, gametic, zygotic life cycles, I teach the
students the different life cycles without the names.  Then I tag the names
on at the end, pointing where meiosis occurs.  This at least gives them
something meaningful to hang the name on. 
        Jeez, can you tell I'm a botanist by how long I rambled on about 3
terms?

Doug Jensen

Douglas P. Jensen, Assistant Professor of Biology
PO Box 9615
Hollins College
Roanoke, Virginia 24020
(540)362-6549
djensen at hollins.edu




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