I put several of the white flowers of the wild mustard in some soup and got ill. I’ve used the leaves before in pesto and have had no problems. Are the white flowers edible?
From your description of the plant (and its white flowers) I believe you are asking about garlic mustard, Alliaria petiolata (see Ontario’s invading species awareness program’s article, Garlic Mustard ). All parts of the plant – flowers, leaves, roots, seedpods and seeds — are edible. So it is unlikely that the flowers in your soup caused you to be ill.
Wild mustard (Sinapsis arvensis L. or Brassica arvensis are 2 of its botanical names) has yellow flowers and is also edible. See Ontario’s Ministry of Agriculture, Food & Rural Affairs’ Wild mustard factsheet.
In the future, if you feel unwell following a meal that includes a plant that you’ve picked (and possibly mis-identified or which might unintentionally include other plants that are toxic), I suggest that you contact your nearest poison control centre as soon as symptoms start.