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Why are bryophytes usually small compared with seed-bearing plants?

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Thick green bryophyte moss covers the trunks of three oak trees in a forest, with fallen leaves on the ground. — Bryophyte Bryophyte moss growing on oak trees.

Bryophytes are generally small because they lack the specialized vascular tissue—specifically xylem and phloem—that seed-bearing and other vascular plants use for internal water and nutrient conduction.12

In the absence of these tissues, bryophytes rely on the surface of the plant for the absorption of water and minerals, and the internal movement of fluids is extremely slow. Furthermore, they lack the structural support provided by lignin, a substance found in the cell walls of vascular plants that allows them to grow to significant heights. Because they also lack a well-developed cuticle to prevent rapid water loss, most bryophytes are restricted to moist environments and cannot support the complex, large-scale body structures seen in seed-bearing plants.132