Blue Mustard (Chorispora tenella)
 
(Common names include: blue mustard, purple mustard, musk mustard and cross flower)
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This is one of my favorite edible plants. It is a shame it dislikes hot weather so much because I really only get to enjoy it for a short time each spring. it will come up early in the spring even when snow is still on the ground. it is often the first plant to take over fields and will soon blanket the area with beautiful purple flowers. It has a delicious radish flavor that will vary depending on the life story of the plant. Well watered and fast growing, this is a great edible in season. I know many do not like the pungent smell of this plant. It is very strong and very distinctive. For me it brings back memories of rolling down mustard and grass covered hills as a child and then there is the delicious radish flavor that is not at all like the scent of the flower.
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Here is the description from Wikipedia Chorispora tenella is a species of plant in the mustard family known by several common names, including purple mustard, blue mustard, musk mustard, and crossflower. This mustard is native to Eurasia but is well known in other parts of the world, particularly in temperate regions, as an introduced species and a noxious weed.
 
This is an annual herb reaching a maximum of half a meter in height and covered abundantly in sticky foliage. The four tiny flower petals emerge from a loose tube of sepals and spread into a corolla about a centimeter wide. The flowers are lavender in color and a field heavily infested with purple mustard can take on a distinct lavender wash. The plant has a strong scent which is generally considered unpleasant. The fruits are long upturned cylindrical capsules about 4 centimeters long containing round, reddish-brown seeds. This is a tenacious weed which can be troublesome in agriculture. It reduces yields in grain fields and when it is consumed by dairy cattle it gives their milk a bad taste and odor. This plant reproduces by seed, so any control method preventing the plants from setting seed is effective.

My Experience
As you can see by the Wiki description, not everybody loves this plant as much as I do. While it tastes great on a sandwich or in a salad it is not going to add a delightful flavor to your milk. If you ahve cows or goats that you milk you will want to keep them away from this one. leather. I first tasted this plant in 2010 when looking for identification of local plants and weeds. it took me a while to ID this plant with the research available at the time but once I did and then tasted it I was very excited! I found another delicious herb to add to my list and my diet. Little did I know that it's season was so short lived.
Now I look forward to this fresh green plant each spring and I greddily pluck it up and add it to my sandwiches and salads through spring. I know all too well from experience that this one simply will not last when the temperatures reach into the 80s. it quickly goes to seed and becomes a nasty spiny tumbling plant that would not resemble anything you would wan to eat.

Additional info and resources