Questions & Answers about Las moras de esta mañana estaban muy dulces.
Literally, de esta mañana means of this morning.
In natural English, that often becomes:
- from this morning
- this morning’s
So Las moras de esta mañana is basically the blackberries from this morning or this morning’s blackberries.
This is a very common Spanish way to connect a noun with a time expression:
- la reunión de esta tarde = this afternoon’s meeting
- el partido de anoche = last night’s match