In the Lower Carboniferous of Scotland Mr Kidston has found several specimens of a large dichotomous thallus, with a very distinct midrib; the specimens, referred to the provisional genus Thallites, much resemble the larger thalloid Liverworts.
Opposed to the thalloid forms are the group of leafy Liverworts (Acrogynae), whose plant-body consists of a thin supporting stem bearing leaves.
The prothalli of the Pterido phytes, which form similar symbioses, show a somewhat different mode of arrangement, the Fungi occupying the external or the lower layers of the thalloid body.
I, End of hydroid of the thalloid Liverwort Blyttia, showing the thick lignified wall penetrated by simple pits.
The gametophyte is a small thalloid structure which shows varying degrees of independence affording an interesting transition to the next group.
It is true that certain Bryophyta (Marchantiaceae, Anthoceroteae) possess a thalloid structure similar to that of Thallophyta, and are at the same time possessed of the colouring matter of the Green Algae.