Algae vs. Plants

Diagram of algae

Plants and algae are both photosynthetic. Both are also considered eukaryotes, consisting of cells with specialized components. They both also have the same life cycle called alternation of generations. However, algae are not plants. So, what are they? They are merely members of the Kingdom Protista. Plants compose their own kingdom, Kingdom Plantae. While plants and algae may sometimes appear to be quite similar visually, they in fact have a number of differences between them. In terms of where they live, how they survive and reproduce, and what composes them, plants and algae are vastly different.

Did you know that seaweed is not a plant? First of all, algae may be unicellular, colonial, or multi-cellular. Plants, on the other hand, are only multi-cellular. Holdfasts, stapes and blades compose multi-cellular algae. In comparison, plants have roots, stems, leaves, flowers, fruits, seeds and cones. The roots of plants not only hold them in place, they nourish them. Plants possess vascular systems, which allow for the uptake and transport of water and nutrients. In contrast, each cell in algae must obtain its own nutrients from water for survival.

Diagram of plant vascular system

Clearly, plants cannot move, as they are rooted to the ground. On some algae, holdfasts, which are comparable to the roots of plants, hold them in place. Some algae drift with the water currents. Some algae are actually actively mobile. Dinoflagellates, for instance, whip themselves through the water with a tail-like structures called flagella. Other algae may move by pushing their bodies forward in a crawling motion.

Algae

Typically algae are found in water; although, they may be found on land or snow and, strangely enough, even growing in rocks or marine animals or on the fur of some rainforest animals such as sloth. Plants are generally found on land; however, they can also live in water, such as eelgrass in marine systems and water lilies in fresh water.

Reproduction could not be more different for plants and algae. Plants have complex, multi-cellular reproductive systems and some even require the assistance of wind, birds, or bugs for pollination. Algae, comparatively, can reproduce through tiny spores or even by replication or the growth of broken pieces.

Eelgrass is a submerged aquatic vegetation (plant)

Despite all of their differences, algae and plants can often appear deceptively similar. So, next time you’re on the beach and you come across what appears to be a plant, take a second glance because it may in fact be algae.

~Elizabeth Gooding