21w05a (the first snapshot in the fifth week of 2021) was released and adds various cave plants, but do note that they do not yet generate naturally as the new cave biomes are still to be properly implemented.
A new leaf type, azalea, has been added, along with a small azalea bush block, both of which also come in a flowery variant.
The azalea bush grows from a moss block, which when fertilised spreads to nearby blocks and creates plants around it.
The moss block can be crafted into a moss carpet, a thin variant of moss used to cover the ground.
In watery areas, the dripleaf plant may be found. This block cannot support your weight, and will slowly tilt if you stand on it, eventually dropping you to the ground.
In caves, there is a new vine, which grows glow berries, which give off light, obviously. These berries can be harvested and eaten, especiallyby foxes.
Also growing from the ceiling of caves will be the large spore blossom flower, as well as hanging roots that grow from rooted dirt.
That's it for the new blocks, but there are also some other changes in this update.
Skeletons that fall into powdered snow will now slowly turn into the snowy stray variant.
The names of copper blocks have been changed, as they were previously very long. Waxed Lightly Weathered Cut Copper Stairs was a doozy; it is now Waxed Exposed Cut Copper Stairs – slightly better.
Various new events now trigger a sculk sensor (the vibration detection block), such as block entities like paintings being placed, shulker boxes opening, bells ringing, or a mob being interacted with.
For a summary of changes in this snapshot in a visual form, see my update video below: