Pixelmon Mod

The thing next to Bulbasaur in this image. I've seen these things all over in Forest biomes. There seems to be a single block inside it that has an oversized texture on it. I broke the block with an iron pick but nothing dropped. What are they?

You level up eevee near them and they evolve, you can find a similar one in taiga

Thank you. It's been confusing me and my friends ever since we saw them. And searching for info was impossible since we weren't even sure what to call them.