Well, I've found a new plant, but I can't tell you much about it yet. I'm calling it Trollweed for now. It is clearly a new species, but it can't be harvested and drops no seeds!
I've grown this plant 3 times now by crossing stickreed with stickreed but have never got any seeds from it. I've been able to reproduce it by crossing itself in situ with more stickreed.
It's a pale green like reed, but starts looking a bit like flowers and matures into a small pale green shrub that looks a bit like marijuana stalks to me... No screenshot for now, later hopefully.
I have cyazint, blackthorn, venomilia and stickreed so far. Based on the tiers given, I've been working on mass-crossing stickreed, venomilia and cocoa with each other and themselves to find new, higher tier crops. Cocoa seems to have the harshest restrictions on growing conditions and more often than not I can't replace it. (I'm working outside on a hydrated field in a moderate biome)
Either Trollweed has very low seed chance, or there's something I'm supposed to have worked out about how to grow it. GRR! All I can do for now is keep crossing it in situ and hope to evolve past this PITA plant.