We were saving a lot of seeds of true Wasabi (Eutrema japonicum) the last days. The seeds develop the first half of May and have to be harvested before they fully ripen because the seed pods open and they seeds fall out.
Wasabi is in the Brassicaceae family and what is normally harvested are the stems of certain varieties with big stems. The ones we have growing don't have big stems but the leaves are also tasty in salads for example and have a milder flavor. In many products Wasabi is supplemented with the easier to grow root of Horseradish (Armoracia rusticana), which has a spicier but less interesting taste.
Wasabi likes to grow next to cool mountain streams in the woods so it can root to the water. It dislikes hot weather and the seeds are easily germinated after a period of stratification.
Saving the seeds is a lot of manual work as the tiny pods have to be peeled by hand and the seeds are easy to squeeze. We were able to harvest about 100 - 200 seeds per 15 minutes and after 2 days of work for one person we ended up with a half full little jar containing approximately 5000 seeds. The seeds are stored in a fridge until they are shipped so they stay fresh as they quickly lose viability. They are going to be sold for 25 $ per gram.