Nuphar polysepala Engelm. is a infrequent aquatic plant of lakes in the Sierra Nevada, and even less frequent elsewhere in California along the coast. The southerly distributional limit is in the vicinity of Oso Flaco Lake, San Luis Obispo County where rare aquatic plants such as like Rorippa gambelii and Arenaria paludicola are found. The recent "An Annotated Checklist of the Vascular Plants of Santa Cruz County, California" (2005) does not attributed Nuphar polysepala to the county, although in "Flora of the Santa Cruz Mountains of California" [J.H. Thomas, 1961] this pond lily is attributed to "San Francisco, Pescadero, Watsonville and Big Basin". None of these sites is vouchered in the Consortium of California Herbaria database [another example of the deficient aspect of not having CAS data].
The Watsonville location is confirmed by William H. Brewer, who in his notebooks associated with the Geological Survey of California collections at UC/JEPS, noted it grew in "the laguna near Watsonville". On August 4th, 1861, Brewer left camp at San Juan Bautista, and rode to Santa Cruz, passing out of the mouth of the Pajaro river en route: he noted its presence. It is uncertain to which present day lake Brewer's reference to "the laguna" , Pinto Lake, Kelly Lake and Kelly Lake are candidates, while College Lake and Lake Tynan are similarly implicated (it was a time of no local placenames, and Brewer's party was of course making the first real maps!).
Today, Nuphar polysepala is extirpated from Santa Cruz County. The pre-settlement presence of Nuphar implies also that a boreal marsh florula might have been present locally, a habitat of course extirpated. Plants like Rorippa gambelii and Arenaria paludicola come to mind...were they once present also?
The San Francisco record is reported by Behr (1888, Flora of the vicinity of San Francisco) as near the "Marine Hospital", presumably some now filled pond on the present day Presidio. Brewer also collected Nuphar polysepala in Marin County (UC133092) at Olema Lake, Marin County on October 2nd, 1861. The recently revised Marin Flora does not report it extant there, and also reports other potentially extirpated sites in that county.
Overall, the collective record indicates that many former coastal sites for Nuphar polysepala
are now extirpated, as are other lowland sites. I have seen Nuphar polysepala in the vicinity of Locke, San Joaquin County as recently as the early 1970s – is it still extant in the Delta, or has it succumbed there to salinization? Perhaps Nuphar polysepala
belongs on CNPS List 2 to insure it is afforded adequate assessment