A standard humic acid extraction procedure has been used to isolate da
rk brown organic residues from samples of the macroscopic marine brown
alga Pilayella littoralis. The residues are insoluble in water, but s
oluble at high pH, and are similar in elemental composition, ash conte
nt, UV-visible, IR, PMR and X-Ray fluorescence spectra, X-Ray diffract
ograms and scanning electron micrographs to residues of a humic acid i
solated from municipal compost. These results indicate that Pilayella
produces humic acids.