Oh! Somehow I missed that paragraph :B
Transform formulae are in the third and last drop-down :) ... They aren't shapes in themselves, they only manipulate other formulae somehow. Actually, I'm not seeing Fern in this one! ;P It's all Menger... Unless that odd layering is the Fern doing something... =)
Ahhhh ok!
I think the fern maybe changed the shapes that are making up the larger structures? I guess you can't see them in this render because they're so tiny but if I drop the number of menger integers I can see the individual shapes better and they change shape on tweaking fern.