Some similarities to : Creeping Jenny (to which it is related) but yellow pimpernel has petals that are (when not closed in cloudy weather) more pointed, have more space between petals, and are not cup-shaped. It also has styles that stick out much more prominently upwards from the flowers. Also, Creeping Jenny has square stems whereas they are round in Yellow Pimpernel.

Obvious resemblance to : Scarlet Pimpernel, (Anagalis arvensis, to which it is related) except that it is in a differing genus and the flowers are yellow (not scarlet red).

Despite similarities in appearance and highlighted in its common name Yellow Pimpernel, it is not directly related to Scarlet Pimpernel (Anagallis arvensis) being in a differing genus (but still within the same Family (now Primulaceae in APGIV). Yellow Pimpernel(Lysimachia nemorum) is in the same genus (Lysimachia) as some other yellow-flowered plants: Creeping Jenny (Lysimachia nummularia) with some being far taller - the Loosestrifes, such as Yellow Loosestrife (Lysimachia vulgaris).

Apparently Yellow Pimpernel is poisonous but your Author can find very little information on which particular constituents it possesses. Triterpenoid Saponins in the roots are mentioned, but are not specifically named!

The Lysimachia genus contains plants containing, one researcher says, HydroxyCinnamic Acid, Saponins, Flavonoids, Tannins and the BenzoHydroquinones Embelin (which is orange) and Rapanone, which is not much to go on. Your Author guesses that Yellow Pimpernel has not been much researched. Note that it is the Lysimachia genera overall which contain these; Yellow Pimpernel is not specifically mentioned as containing any of those, although it might...