Vascular Tissues

The importance of ferns can be summed up in two words: vascular tissues. Ferns and related groups are the oldest organisms that still exist that evolved vascular tissues, which are specialized tissues adapted for carrying water and nutrients. This may seem like a rather minor detail, but the ability to transport vital components for life can have a major impact on the structure and ecology of an organism.

Because ferns gained the ability to transport water, they were able to grow larger. A limiting factor to the size of bryophytes was the fact that water could only move through their tissues by simple diffusion, which is a rather slow process. So, if a bryophyte was large, then the cells farthest from the water source might die before the water had a chance to diffuse to it. Ferns, however, have a mechanism that allows for a quicker, more efficient form of water transport, so these plants can become quite large without risking the death of cells.

Also, though larger organisms diffuse water into their tissues rather slowly, they also lose water slowly. Ferns have structures called stomata, which allow them regulate the amount of water they lose. By closing these stomata, they can greatly slow water loss. This means that ferns are more resistant to dessication during times of a water shortage. So, this allows ferns to live in areas where water is not always abundant, allowing them to move into habitats from which bryophytes are restricted.