Got any pics? Not being familiar with this particular species, I googled it, and the pics are very similar to some of my locally collected P. palustris. My palustris has leaves which can be quite variable, in some cases looking very similar to the pic I saw of the pectinata. I wonder if the pectinata is also variable?It really is great fun! Just this Thursday I found some Proserpinaca pectinata (Comb-leaf Mermaid weed) and some more L. glandulosa while at work. No pictures because the camera died and I couldn't get "natural" photos. But I'll go back there and get some good shots in a few weeks.
One of these days I will try to take some close up pics of my palustris. Part of the stem will have leaves very siimilar to what the pics here show, then another part of the stem, usually higher up, will look different.Compare these plants to the Proserpinaca palustris above. I think these are P. pectinata, but I can no longer confirm it as I didn't save any seeds/nuts and there were none left when I got out there yesterday. The specs of this particular site: frequently flooded soils, there was a 2-month dry spell where most of the plants were left above water and began forming emergent growth. The pictures were all taken 2 days after a 5" rain. I'll post pics of other plants in a new post.