This plant is very similar to slender marshpink.
A good field mark is the length of the sepals (the
green projections seen along the edge of the petas).
Slender marshpink has sepals that are equal to or
longer than the petals, rose-of-plymouth with
sepals that shorter than the petals. Useful
information as the plants sometimes grown in the
same vicinity.

Image ID 070214-2915