In responding to changes in developmental and environmental cues, gene expression is altered through alternative splicing, an mRNA maturation process. During splicing, regions of pre-mRNA between splice sites are removed. Splicing factors, such as Serine/Arginine-rich (SR) proteins, bind to RNA and influence splice site utilisation. SR proteins are known to be generally involved in stress responses; however, little is currently known about how SR proteins influence splice-site choices. SR proteins in plants are highly redundant, which has made their characterisation very difficult. Taking advantage of Marchantia polymorpha, which harbours fewer members of SR proteins, we show that knocking out specific SR proteins confer varied phenotypes, including loss of thermal response, changes in size associated with differential gene expression and differential splicing. Our results highlight the power of M. polymorpha in inferring biological principles from complex gene regulatory events such as splicing. This work is the important preliminary steps needed to understand SR protein-specific effects on alternative splicing.