Seaweed gels and land plant gels.
We all know that seaweed gels have properties different from land plant, and that they occur in a rich variety of forms, which starch and cellulose do not. Chemically the reason is, that marine algae have other sets of pigments than land plants have. Biologically they have so, because the red fraction of light, which is utilized by land plants, does not penetrate to the depths, where most algae live. In consequence other sugars are produced at photosynthesis than by land plants and by green algae, and these sugars are plymerized into other polysaccharids; to sum up we call them phycocolloids. If you want to stress their relationship to the assimilation products of higher plants, you may classify them as hemicellulose. If you wish to call attention to their qualities as stabilizers and emulsifiers, you may simply call them gels. While starch is very monotonously built up by maybe 30, maybe 1100 identical alpha-glucose sugar units, and cellulose by 11 000 identical beta-glucose, gums from red algae are polymerized from a variety of different sugars, essentially galactoses and related compounds, like galactose sulfate, anhydrogalactose, methyl- galactose, galactopyranoes and so on, causing a very rich variety of polymers with different qualities. Occasionally ramnose, xylose and other sugars are included. The proportions and arrangements of these units differ from different genera, species, nuclear phases and local collects.