the classification of living creatures as plant,animal,or cell-like in structure,continues to be problematic for the world's scientists.
even seemingly simple decision such as the placement of a species into a kingdom may be the subject of heated debate.
a perfect example of this classification dilemma is the group of organisms commonly known as algae.
algae are usually thought of as a type of aquatic plant or slimy substance.
in latin, the name algae means "seaweed," and yet not every type of algae takes the form of a weed or live in the sea.
some varieties live in soil and can withstand long periods without water; other live in snow or inside other animal species.
though scientists agree that there are four types of algae,each distinguished by different pigmentation,the classification of all but one type remains precarious.