Bonjour
may be in winter your greenhouse is probably too cold, dorstenia are rather tropical plants from africa and central and southern america.
for my part I always cultivate them at temperatures higher than 16 ° C (outside in summer) , with waterings all year long (keeping a dry substrate between each watering)
the rubiaceae ( ant plants) are also tropicals plants ,from South East Asia.
I cultivate these species in 2 terra , always with a good air hygrometry (80-90%)is grown a little like nephentes, since from the same backgrounds.
I've been cultivating them for several years now, and I'm looking to swap