Steve, I'll let Jan handle the tricky and subtle questions regarding
botany. This is a question for....(fanfare and drumroll please) an
astronomer!
No one seriously believes in this hypothesis. It can be argued against many
ways. When looking at the possibility that VFTs have extraterrestrial
origins, consider the following perspective. VFTs function essentially the
same as do all other forms of life on Earth. They are cellular, they operate
with the same set of amino acids, they use the same trick of genetic coding
with chromosomes, and even use the same molecules (DNA, RNA) in this
information storage and access. In a broad perspective, humans are
essentially identical to apes and penguins and plants. We all operate on
the same chemical scheme.
If a life form of extraterrestrial origin plopped down onto earth, it
would have evolved with different environmental constraints and would
certainly be very different in a huge number of biochemical ways. The
fact that VFTs are essentially identical to all the forms of life on
Earth tells us they have the same origin as terrestrial life.
NOW, there is the possibility that all life on earth is of an extraterrestrial
origin (space germs), but that is a hypothesis with no evidence to suggest it,
and no reason to be invoked.
Barry
P.S. Organic molecules and amino acids have been detected in extraterrestrial
objects, and the ever-goofy Fred Hoyle has noted that some unidentified
absorption features seen in stellar spectra might be caused by freeze-dried
_E.coli_ floating in interstellar space---some sort of cosmic spawning agent??