How does the Fuligo Septica obtain food?

It does not feed on living plants. It is a saprobic organism that uses the microbes in the mulch and on leaves and other surfaces as its nutrients.

They exist in a nature as a plasmodium, a blob of protoplasm without cell walls and only a cell membrane to keep everything in. It is really nothing but a large amoeba and feeds much the same way, by engulfing it's food (mostly bacteria) with pseudopodia ... the plasmodium of Fuligo Septica is transparent, like an egg white.