The Erebus is filled with many exotic creatures and magnificent trees; the same is also true for the smaller varieties of plant life. These plants can be found in the most to the least hospitable of areas (so, Underground Jungles to Volcanic Deserts and everything in between).
Nettles have their own page.
Weeping Blue Bell Edit
Their only use is for the petals they drop; these petals are used for a Smoothie.
Found alongside lakes in Underground Jungles and Submerged Swamps, Bullrush is the sole provider of Papyrus in the Erebus. Rarely, when broken, it will drop this Papyrus, which can be used for a few things.
If broken using Shears, they can be used to farm Papyrus by repeatedly placing and breaking them, as they drop Papyrus alongside themselves if broken with Shears, just as Leaves-both vanilla and not-drop Saplings and Apples (if Oak leaves) when broken by hand or with Shears.
Droughted Shrub Edit
Exclusive to the Ulterior Outback, these shrubs are very dry and look like dead Long Grass. That's pretty much it, really; they serve no purpose other than aesthetics.
Desert Shrub Edit
An extremely rare find in Volcanic Deserts, Desert Shrubs serve no more of a purpose than Droughted Shrubs, but they look like very dry Ferns instead of Long Grass.
Tall Bloom Edit
These flowers are, as their name suggests, tall. Not three blocks tall, just two, but the name stems from (pun intended) their appearance; Tall Blooms have very long, thin and windy stems leading to their flowers.
Need more be said? Ferns are another type of fancy Long Grass found anywhere there's more Grass than Sand in the Erebus, and also have a chance of dropping Seeds or Cabbage Seeds. There's nothing more to Ferns than that.
Quite possibly the coolest-or should I say hottest-flower in the Erebus, Fireblooms are found solely in the Ulterior Outback. They are useful as they provide the capability to make Blaze Powder (by combining nine of them in a crafting grid) as well as being used for a Smoothie.
Fireblooms emit a small flame from their flower, but do not shed light.
Swamp Plant Edit
Fancy Long Grass, basically. Same chances of dropping either kind of Seeds. Found only in Submerged Swamps.
A tricky variant of Vines, Thorns are found only in Underground Jungles growing from the trunks of Mahogany Trees. They can be climbed like Vines, but inflict half a heart of damage per second whilst doing so.
As with Vines, they can be collected with Shears and are exceptionally useful for sadistic parkour maps and gauntlet challenges.
The plant equivalent of Mould, Moss grows just about everywhere that has water. It can be made into Moss Balls (which have no purpose as of yet) and works as a wonderful material for Composters to turn into Compost.
Cultivated Moss can also be made to speed up the grow of Moss drastically, same as Mould.
Glowing Swamp Weed Edit
These weeds are found in-you guessed it-Submerged Swamps, hidden at the bottom of the giant rivers that dominate those biomes. They can be collected without use of Shears and can be placed underwater without breaking.
Glowing Swamp Weeds are very useful for natural lighting, as they emit a light level of 14 and actually look more like some exotic plant (which, as we know, they are) than a stereotypical weed.
Swamp Algae Edit
Found only on the surface of rivers and lakes in Submerged Swamps, Swamp Algae is quite ugly and serves no purposes at this time.