I've noticed that some imperfective verbs are converted to the perfective by just adding a prefix. However and oddly enough, sometimes there's an alternate imperfective formed from an internal modification of the prefixed verb itself!
I'm not taking into account verbs in which the prefix conveys a different meaning rather than just changing the verb aspect.
делать, meaning "to do", is imperfective; if we add the prefix под, the word becomes
подделать, which is perfective and means "to falsify". If we want to change the new verb to imperfective once again, then an internal modification is required, and thus it becomes
Now to the point: the verb цвести ("to flourish") is imperfective and its perfective counterpart is расцвести. However, it seems that
расцвести accepts two imperfectives: both the "original", unprefixed
цвести, and a variation from the prefixed verb itself: расцветать.
The same goes for растянуть, which, apparently, accepts both тянуть and растягивать as imperfectives.
However, is there any difference in meaning, or are both imperfectives interchangeable?