They lack specialized vascular tissues (xylem and phloem) for transporting water and nutrients, limiting their size and requiring a moist environment.

Here's why:

* Lack of vascular tissue: Nonvascular plants, like mosses, liverworts, and hornworts, do not have the specialized tissues (xylem and phloem) that vascular plants use to transport water and nutrients throughout their bodies.

* Limited size: This lack of vascular tissue limits their size. They are generally small and low-growing because they rely on diffusion and osmosis for water and nutrient transport, which are slow processes that only work over short distances.

* Moist environment: Nonvascular plants need to live in moist environments because they absorb water directly through their surfaces. They are particularly vulnerable to drying out in dry conditions.

Let me know if you'd like more details about nonvascular plants!