Chris,
Absolutely nothing would make you say that. BUT, if you kept walking
and discovered that large populations of plant A and B existed, while in
contrast plant C is much rarer and occured primarily where the ranges of
A and B overlap, then you might start wondering. If you knew that it were
possible for A and B to interbreed, you might wonder further. If C is
found in disturbed regions, wonder further. And if C is intermediate to
A and B, wonder still further!
Eventually, after all this wondering, you may conclude that plants A, B, C
would be better called A, B, and A*B.
There is also the possibility that plants A, B, and C all belong to a larger
variable species.
Field work. Field work. Field work.
Barry