How to distinguish Anagallis foemina and Anagallis arvensis:
1a - Petals red or blue, obtuse or truncate at apex. Glandular hairs on petals margin many and dense, 3-celled: A. arvensis.
1b - Petals blue, often subacute at apex. Glandular hairs on petals margin lacking or few and scattered, 4-celled: A. foemina.