In this revision 4 endemic species, one with two varieties, are recognized from the alpine and subalpine regions of New Guinea. Isoetes stevensii Croft, I. hopei Croft, and I. neoguineensis Baker var. rheophila Croft are described as new. Scanning electron micrographs of the megaspores and microspores, which furnish important diagnostic characters, are presented for all the taxa in Papuasia as well as for the possibly related species, I. philippinensis Alston.