藻类(algae)
一群主要是水生的、能行光合作用而无法精确定义的有机体。大小不一，从显微镜下的单细胞鞭毛虫，到长达60公尺的大型褐藻。藻类提供了地球上大部分的氧气，是几乎所有的水生生物的食物基地，并提供食品和工业产品，包括石油产品。它们的光合作用色素比植物的更为多样，它们的细胞中具有植物和动物所没有的特点。随着新的分类法资讯的发现，藻类的分类也在迅速改变。以前，藻类按它们叶绿体里的色素分子分成红藻、褐藻与绿藻三类。现在辨认出的种类远远多於这三类，每一种都有共同的色素类型。从演化的意义上看，藻类彼此间的关系并不密切。某些种群与原生动物和真菌的区别只在於它们有叶绿体以及能行光合作用的能力，因此从演化上来看，它们与原生动物或真菌的关系比与其他藻类的关系更为接近。利用藻类的历史或许与人类的历史一样悠久，沿海的居民食用海藻，许多餐馆里都提供藻类食品。它们常见於溪流中「黏滑的」岩石上（参阅diatom），是池塘上绿色光辉之源。
English version：
algae
Any of a group of mostly aquatic, photosynthetic organisms (see photosynthesis) that defy precise definition. They range in size from the microscopic flagellate Micromonas to giant kelp that reach 200 ft (60 m) in length. Algae provide much of the earth's oxygen, serve as the food base for almost all aquatic life, and provide foods and industrial products, including petroleum products. Their photosynthetic pigments are more varied than those of plants, and their cells have features not found among plants and animals. The classification of algae is changing rapidly as new taxonomical information is discovered. Algae were formerly classified into three major groups—the red, brown, and green seaweeds—based on the pigment molecules in their chloroplasts. Many more than three groups are now recognized, each sharing a common set of pigment types. Algae are not closely related to each other in an evolutionary sense. Specific groups can be distinguished from protozoans and fungi (see fungus) only by the presence of chloroplasts and their ability to carry out photosynthesis, and thus have a closer evolutionary relationship with the protozoa or fungi than with other algae. Use of algae is perhaps as old as mankind; seaweeds are eaten by coastal societies, and algae are served in many restaurants. They are common on “slimy” rocks in streams (see diatoms) and as green sheens on pools and ponds.