Just another guess; maybe some thing in the Allium group. According to sources Allium tuberose or its relatives are used in cooking. Crush the leaf and give it a sniff test and see if it has an onion/garlic smell. Again I’m only guessing, link below is for some of the Allium vaieties. Best wishes! https://www.google.com/search?q=Allium+tuberosum+bulb+seeds&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjEhavxpZ_TAhUKwWMKHXrSDQgQ7AkIcQ&biw=1722&bih=833#imgrc=_

Link to P. geminiflora. If none of these plants match when it blooms, please give us an update. And if you still don’t know by then post photo of flowers. http://pacificbulbsociety.org/pbswiki/index.php/Polianthes

Link for tuberose P. tuberosa. http://www.metro-greens.in/2016/06/rajnigandha-care.html

Thanks for the up date! One of the possible plant that Walter mentioned is’sedge’. Link below is for some of its seeds images. As for my eyes the seedling is still to young to be certain, but with the appearance of second sheath(?), I could only speculating and suggest you also check out some of the species in the Polianthes group i.e. Polianthes tuberosa & Polianthes geminiflora varieties. Links will be follow in the next posts. Best wishes! https://www.google.com/search?q=sedge+roots+%26+seed+image&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjOx5H1-Z7TAhVHx1QKHVIEACQQ7AkIRw&biw=1722&bih=833#imgrc=5hodSXCH5spsHM:

maybe a sedge or reed?