Physcomitrella patens, also known as Physcomitrium patens, is a spreading earthmoss that was the first among seedless plants to have its entire genome sequenced. This, as well as its efficiency in homologous recombination, makes P. patens an excellent model organism for studying plant genetics and plant development through knockout moss. One such line of moss, P. patens mGPF-ER, expresses the endoplasmic reticulum through modified green fluorescent protein (mGFP), which serves as a marker to visualize the ER network in the cell. Among P. patens mGFP-ER, its protonemal cells are the most suitable to use in microscopy research, therefore, being able to promote specific cell types, such as protonemal cells, through varying growth media, allows for focused and efficient research. Furthermore, the ability to use P. patens mGFP-ER in oxidative stress studies can bring more insight into how stress in plants can affect varying organelles, such as the ER network, within the cell.