Plants, vines, moss, grass, and algae.
I remember de_aztec being one of the greenest Counter-Strike levels, but I never noticed how economical they were with their green things. There’s a single plant polygonal model, used many times. There’s two grass textures, displayed using alpha cutout on a billboarded polygon. There’s the vine texture, also an alpha cutout but on a non-billboarded polygon. There’s a tiled moss-on-stone texture. And the last bit is a tiled algae/ground texture at the bottom.
That’s all it took art-wise to make me think of de_aztec as the “green” level.