The lack of palm trees has already been mentioned and Red said that they will be implemented when the corresponding biome is added.
I'd like bougainvilleas or at least a few plants that grow in the south. Maybe those will be added when the jungle biome appears.
We also have many native plants like tulips, carnations, bluebells, hyacinths, daisies, petunias, violet, targetes, geranium, begonia, anthurium, pansies, cowslips, hyacinths, orchids, snowball as a shrub and clematis as a climber.
rose hips, oleander, sloe, lilac, forsythia
I can no longer stand the pink or blue flowers that are available at the moment, flowering plants that fit in balcony boxes would be fine.
Lavender and a few garden herbs would also be nice; the latter can be used for cooking.
We have some very nice plants in the game so far, but unfortunately, some are still missing for the existing biomes, including flowering plants.
Tree: beech
I miss the flowering plants that existed in Java, like broom. You could simply paint them into the world like grass, and everything looked beautiful afterwards. The broom probably required far fewer resources than planting blue and red flowers everywhere. It was also much, much faster to paint.
I keep trying to plant plants in flowerpots, and that works quite well. Unfortunately, the self-made flowerpots don't have collision, which means that if you're not careful, the leaves will stick out of the flowerpot.
I hope my additions are ok in this post, I didn't know if this should be a complete list, so I wrote my comments. 
