I have been noticing mustards in pairs this year. Earlier in the year, within a short period of time I noticed two different kinds of mustards growing near each other in similar habitats. Then I noticed this mustard and the yellow flowered mustard in the same habitat at the same time (though I had noticed each quite awhile before they were recognizable to me as mustards), and later still I have found two more types of plants, that while not having flowered yet look to me like mustards, growing near each other.