Question

what is meant by thallus in bryophytes ?????

Answer 1

Thallus is the plant body that is not differentiated into stem,leaf or roots.
In broyophates we dont have such divisions . 
so bryophytes are also called as thallophytes

Answer 2

A thallus is a multicellular plant body exhibiting little differentiation of tissues and lacking such organs as roots, stems and leaves. The thallus is derived from cell divisions occurring in more than two planes. This results in a fairly complex three dimensional plant body that varies in thickness and in shape.