Pictures of these structures
Like all red algae, B. farlowianum has a miraculous
life history which a encompasses three distinct phases. To see a pictoral
representation of the life history, use the Life
History link. B. farlowianum has an alteration of generations
completely different from the other non-red algae.
While the tetrasporophyte and gametophyte look almost exactly
alike, except for the arrangement of sori, there is one distinct life
stage. The carposporophyte stage, unique to the Rhodophyta, is one in
which the offspring are produced which live, parasitic on the mother,
until they reproduce themselves.
We will begin with the haploid gametophyte stage.
Sexual reproduction in Botryoglossum is oogamous.
The male gametophyte releases his non-motile spermtia into the sea. (All
Rhodophyta are without flagella, even in their sperm stage.) The inability
of the spermatia to propel itself is one possible reason that B. farlowianum might
prefer more turbulent waters. These spermatia are thrown around by the
tides until they have the good luck to stick to a female gametophyte,
and fertilize her egg.
The egg cell is called the carpogonium. This is supported
by a large auxilliary cell, in a three-cell complex. There is also long,
thin, hair-like cell growing up from the oocyte, called a trichogyne.
This added surface area to catch onto increases the spermatia's chance
of hitting upon an egg cell.
When the egg is fertilized, the carpogonium and the auxilliary
cell fuse, creating one large fertilized diploid oocyte. Gonimoblast filaments
shoot out from the egg cell to various parts of the plant, producing multiple
zygotes. This makes the most of any fertilization event, to counter the
low chances of the spermatia reaching the egg. At each gonimoblast filament
end, a large, round carposporophyte is formed, which holds many diploid
spores. The parasitic carposporophyte relies on the mother for all its
nutrition while alive.
When the carpospores become mature, the carposporophyte
becomes a large bulge. It protrudes out to one side of the thallus, and
eventually bursts through, expelling the carpospores to the outside. These
then well land on a suitable substrate and grow up to be a diploid tetrasporophyte.
The tetrasporophyte plant looks just like the gametophyte
plant, which is why B. farlowianum is termed an isomorphic alga.
The tetrasporophytes produce tetrahedral haploid tetraspores through
meiosis, which, when released, grow into haploid gametophytes. For
a pictoral version of this explanation, go to the Life