I love doing this scientific art activity with my Grade 9 classes. It's great because it has connections to the Biology and Astronomy units in our curriculum. I typically use it to bridge the gap between those two units, or when I teach about the Sun.
The kids learn while making cool art that we display in the classroom. A large group of Grade 9s will be done this in less than 30 minutes, so you'll want to adjust the amount of time for your grade level (I would say start around Grade 3 for this activity).
I use the Nature Print Paper from BLICK, but there are other sources too. Honestly, I think I ordered these in my first year teaching, and I still have a bunch leftover from my first order. That being said, I usually cut the 5x7" pages in half.
BLICK also offers a tutorial video and lesson plan for this activity.
This is something fun you can do in your Science or Art classes when students finish early, too!
Which one is your favorite? Don't tell my students, but I think the lizard one is so cool - it's my personal fave! Honourable mention to Sierpinksi's triangle!