What does gen. nov., sp. nov. on scientific papers defining organisms?

Question

I guess that it means genus and species and that nov is novel, but what does it mean if I find a species that just says acidiphilium spp. without a genus, or is this the genus? How can I find out? Finally, is

sp. different from spp. ? many thanks in advance...

Answer 1

If you see Acidiphilium spp., that means there are likely multiple species of the genus Acidiphilium and the researchers did not identify beyond the genus level.  If you see Acidiphilium sp., that means there is only one species, but the identification to species level is uncertain so they only use the genus.

You are correct in your description of the gen. nov. and sp. nov.