Isoetes riparia Engelm. ex A. Br. - Shore Quillwort
This species has also been historically reported from unspecified localities in Hudson, Sussex, and Warren Cos., NJ.
This species is possibly more common than the map would indicate. Due to its diminutive stature, its emergent/submerged habitat, and often encountered sterile state (megaspores required for positive id), it is possibly under-reported/collected.