Final answer:
The size of plants is primarily limited by the lack of vascular tissues. Vascular tissues transport water and nutrients throughout the plant, and without them, plants cannot grow large. This characteristic is evident in nonvascular plants like bryophytes.
Step-by-step explanation:
Limiting Factors for Plant Size
The characteristic that limits the size of plants is the lack of vascular tissues. Vascular tissues are crucial as they transport water, nutrients, and food throughout the plant. Most prominently found in nonvascular plants, like bryophytes, the absence of xylem and phloem means these plants cannot effectively transport water and nutrients, especially over long distances, which limits their growth and results in smaller stature. Hence, nonvascular plants typically inhabit moist environments, which compensates to some extent for their inability to transport water and nutrients effectively.
Vascular tissue is a hallmark of more advanced plant forms, enabling greater height and size. It includes xylem, which moves water and minerals from the roots to the rest of the plant, and phloem, which distributes sugars from photosynthetic parts to other areas. Without this system, plants remain low to the ground to minimize the distance over which water and nutrients must move by diffusion or capillary action. This evolutionary advancement is absent in nonvascular plants, setting nonvascular seedless plants apart from their larger, vascular counterparts. Therefore, while features like the presence of pollen, seeds, or flowers can impact a plant's reproductive success and distribution, it is the lack of vascular tissues that primarily limits their size.