I never saw a blackberry this size and form. In my country they have the shape of the one just before the center of the picture. They grow a bit more as they turn black but that's it.
You missed the part where it strangles every other plant around it, and grows back regardless of how aggressively it's removed. Also the stabbing, lots of stabbing.
When I was a kid, we moved way out into the country, with a man made lake kinda smack in the middle of the property (we weren’t well off, my parents were just boomers with no sense of money).
On the other side of the lake was about 3 acres of blackberry brambles and literally nothing else.
My mother… decided we kids needed to harvest it every single year for jelly, because she wasn’t about to do it and get mangled.. we were required to get 5 gallons each every month they grew.
And now if I never see another blackberry, it’ll be too soon. None of us even really liked blackberry that much.. she gave most of the jelly away.
I think they're delicious when they're ripe, but I'll only harvest the easiest, safest ones around the edge of the bush. That job you and your siblings did sounds hella painful. The thorns will sometimes snag me when I'm hiking and it's like peeling a layer of needles off my skin when removing the vine.
That property sounds like a wonderful place to grow up though. Lots of land to explore, and a lake to swim in? Yes please!
I was eating blackberries from the forest yesterday, and spitting the seeds out as I walked around my yard, and then I realized in horror what I was doing.