Family: Ophioglossaceae.
Cosmopolitan, growing in North and South America, Africa, Asia, Europe and Australia.
Rare. Grows on damp soil, sometimes with moss. I have not seen it for many years. It is small and could readily be overlooked.
Recognise:
It is reputed to spread by means of vegetative buds, and so can form large colonies.
Image: From a specimen growing at Vaughan.