$A$ plant specimen was found without differentiated roots.
$(a)$ Which plant structure helps in attaching this plant to the substratum?
$(b)$ To which group would you classify this plant?
$(c)$ Which plant could it be?

(N/A) The plant structure that helps in attaching the plant to the substratum is called the $Rhizoid$ or the $Thallus$ itself.
$(b)$ This plant belongs to the group $Thallophyta$,as the plant body is not differentiated into roots,stems,and leaves.
$(c)$ This plant could be an $Alga$ (e.g.,$Spirogyra$ or $Ulothrix$).