I really don't know what sort of plants this is!

I really don't know what sort of plants this is!

Observation - I really don't know what sort of plants this is!. Description: Black thin leaves about 9cm tall. Tiny yellow flowers the size of pinheads about 4cm tall. The whole plant appears and grows rapidly in my garden on my cat's poos!

Black thin leaves about 9cm tall. Tiny yellow flowers the size of pinheads about 4cm tall.
The whole plant appears and grows rapidly in my garden on my cat's poos!