[Kaijo]

There are "obviously" new species that do still crop up because undescribed biodiversity is concentrated in little-surveyed tracts of remote tropical rainforest, and the visible spore-producing structures of those fungi might only appear rarely under poorly-understood environmental triggers. So no, they are not all already known about. "Obvious" species new to science are still being described from such locations. Two examples from recent decades I have seen myself, Chlorogaster dipterocarpi, Spongiforma squarepantsii... I know of many more from taxonomic journals. Also I have found some spectacuar mycoheterotrophic plants in the genus Thismia that were only very recently described. Also, there is a high diversity of secotioid hypogeous fungi many of which are "obvious", but you have to be digging around in the soil looking for them to find them, so they are still poorly known.