Question

Why are Bryophytes limited in size?

Answer 1

Bryophytes is a hypothetical taxonomic division, which contains the liverworts, mosses and hornworts. The study of bryophytes is called bryology. They are non-vascular land plants. They are spore producing and not seed producing plants. They do not possess flowers. Though they display considerable diversity in ecology and form, they are devoid of complex tissue organization.

Complete answer
Bryophytes are devoid of conventional vascular tissues, which generally consists of the substance lignin. With the lack of vascular tissues, the plants possess no means of transport of water and nutrients from their lower organs to their higher organs, which serves as the reason for their limited size.
The vascular tissues like phloem and xylem of most higher plants are composed of sclerenchyma cells, which are usually dead with thick lignified cell walls. Their main function is the transportation of substrates and water. Unfortunately, bryophytes lack this tissue system. If they are like normal height plants, they won’t be able to supply water and nutrients to all over the parts of the body.
The minute size and height of these plants help them survive as their essential organs are present close to the water sources and hence, a transport system is not necessary. As they are small, they do require much support and therefore, the requirement for lignin is also minimized.

Thus, the lack of tubular transport system and other genetically inherited characteristics, render the bryophytes limited in size.

Note:
Bryophytes can rely on the diffusion process, for the movement of water in and out of the plant. Some of the bryophytes possess a waxy and protective coating which makes them possible for resistance towards drying. They also have thin filaments referred to as rhizoids, which anchor them to the soil. Rhizoids assist in the absorption of water and mineral substrates from the soil.