Homothallism refers to a way of reproduction that is kind of like having two sets of mommy and daddy genes in one organism!
So, imagine you have a plant, and instead of needing to mate with another plant to make babies, this plant is able to reproduce all by itself. It contains both male and female parts, like owning both a doll and a toy truck.
When this plant is ready to create offspring, it can take some of its male parts and use them to fertilize its female parts. It’s like taking some toy truck parts and connecting them to the doll to make a new toy creation!
This means that the offspring created will be genetically similar to the parent plant, because both the male and female parts that came together to make the new plant were from the same original organism.
Overall, homothallism is just a fancy way of saying that some organisms have the ability to self-fertilize and make babies that are basically clones of themselves!