Probably liverwort,hard to say without photo.

is it one you are having a problem with,just want to identify or know how to grow?

This is not liverwort - It has the appearance of a green wax - as though a green candle had melted into the grass.
It is on closely mown lawn and is spreading in small patches!

Do you have a photo?

sounds like the spores of a slime mould. there are many of these and this is the time of year when the sporulate [produce their spores/seeds]

Thank you to everyone who contributed.