I used something on some of my plants a while back as an experiment (can't remember which item it was now) and all it did was make the plants larger & have sparkly dots on them. Is that an intended result?

It means they're more fertile now.

And yet they don't seem to reproduce...

True. I should have said "technically it means they're more fertile." I never saw a difference either.

Finally had time to work on this. So the way I understand it is.. Results of mutating a plant can be predicted thusly:
Plant #1 (Mela Rare Oak) will mutate into #2 (Four Petal Maple) OR #15 (Red Berries Cactus). Mutating plant #2 (Four Petal Maple) results in either #1 (Mela Rare Oak) OR #3 Cactusbali Bamboo Tree, etc etc but what about plants #14 (Green Ivy Lotus) & #23 (Tahitian Ridged Cactus)? What do they mutate into?

...and does mutating plant #15 (Red Berries Cactus) give you either #1 (Mela Rare Oak) OR #16 (Hibiscus Tiered Cactus)

Yes, that's correct.

As far as I know, the Green Ivy Lotus only mutates into the Goldenberries Caladium and the Tahitian Ridged Cactus only mutates into the Roseceae Fern. I've used the mutation liquid on those and have never gotten anything else. It may be possible that they mutate into each other, but I personally haven't seen it happen.

Been building a spreadsheet of Virtual Town plants & what they mutate into including images. I am currently missing #20 (White Orchid Pitcher Plant), #21 (Tiger Lily Willow Tree) & #22 (Rosacea Fern) Does anyone have images of those 3 plants they'd like to share? Below is what I have so far. Anyone have corrections?

I have number 20, the White Orchid Pitcher plant. I took an in game screen shot and managed to figure out how to edit it somewhat, although not as well as you have. How do I get it to you?

You could post it here & I'll take it from there :-)