London Rocket - Teff
[Khakshir (Persian); Sisymbrium irio]
Caution: This is NOT the "Teff" from which Injera bread is made in Ethiopia and Eritrea, even though it looks a lot like it. This one is a Mustard Seed, not a Grain, and is used in Persia (Iran) and Afghanistan in the making of Sharbat-e Khakshir, a refreshing cold soft drink, and as a medicinal. The dried leaves are used by the Bedouin as a Tobacco substitute. It got the name "London Rocket" because it grew so prolifically after the Great London Fire, and was also found around bomb craters during the Blitz. The tiny seeds are about 0.001 inch wide (0.025 mm) and about 0.0015 inches long (0.038 mm).
More on Mustard Seeds & Oils.
This plant is now a naturalized invasive in California, particularly in the southern third. It is easy to recognize by its yellow flowers, low growth (to 18 inches) and extremely long thin seed pods (to the left in photo). It blooms from June to August, and seeds are ripe between July and September. Photo by ZooFari distributed under license Creative Commons Attribution-ShareAlike v3.0 Unported.
Buying: This "Teff" can sometimes be found in markets serving a Middle Eastern community, though the market I found it in here in Los Angeles (Montrose, actually) serves mostly an Armenian community. In a 3 ounce bag, it cost 2016 US $1.50 / ounce. It was Golchin brand, distributed by Overseas Food Distribution in Chatsworth, California.
Storing: In its resealable bag (or other airtight container, kept away from heat and light, it should be good for at least 6 months.
Using: For Sharbat-e Khakshir the seeds are used whole, mixed with water, a little sugar, a dash of rosewater, perhaps herbs, and lots of ice. Stir it up a little and take a sip. Medicinally, you skip everything except Khakshir and water - medicine isn't supposed to taste good, that would probably reduce its effectiveness.