Agar-agar is. a non-nitrogenous carbohydrate consisting of two polysaccharides namely agarose and agaropectin. It is obtained from several red algae like Gracilaria, Gelidium, Gigartina etc. Diatomite or diatomaceous earth is formed due to deposition of highly siliceous cell wall of diatoms. Heterospory and seed habit are the characteristic feature of Selaginella. Plants of Selaginella are marketed as curiosities in the name of resurrection plants.