The ferns in the genus Pilularia also have lost their leaf blades, with only the grass-like stipe remaining.

[citation needed] The range of the American pillwort is well-established throughout much of California and south-central Oregon.

[citation needed] Recent research has determined that the North American plants normally assigned to P. americana are actually two different (cryptic) species.

The plants in most of the United States range are true americana, while plants in southernmost California and Mexico are different, and are in fact very close genetically to the Australian and New Zealand species, Pilularia novae-hollandiae,[1] and may possibly be eventually regarded as part of that species.

The pillwort also may die out for drier or colder parts of the season, regenerating the next year from the sporocarps.