If a seed isn't clearly identified as to what it will grow into... ie a seed says "A blue seed" instead of "A blue tri-barrel cactus seed" you can use Poppy Dust to ID it...
There are a couple things to be aware of, however...
Plain seeds are bugged right now...
If you use Poppy Dust on "A Plain Seed" it will still say "A Plain Seed"... and you think it didn't work. However, aparently, if you plant the seed in a bowl of soft dirt, then dump the bowl to recover the seed, it will come back ID'd. This is too much trouble for me so I just don't use Poppy Dust on plain seeds right now.
If you use Poppy Dust on a seed that is "Fully Identified", I believe it was using a charge and giving you no more info, because you already had all the info anyway. I'm not positive and don't know if this was fixed. Just be carefull not to waste your Poppy Dust if the seed is already ID'd.
All "Fragrant Seeds" are always Cocoa Plants. There's never a need to ID a fragrant seed because that never changes. It will always be a Cocoa plant.
Have fun.