The "blank" in "Li Sao" without rhyme means that it does not rhyme.
Lisao can be sung with rhyme, but historical records cannot be sung, so it is said to be a non-rhyme Lisao, referring to its good literary talent. It can be called a non-rhyme Lisao.
Lu Xun called "Historical Records" "the swan song of historians, the rhymeless "Li Sao"". This is Lu Xun's evaluation of Sima Qian's "Historical Records", and it is a very high evaluation.
"Li Sao" is Qu Yuan's masterpiece. It has epoch-making significance in the history of ancient Chinese literature and describes Gao Jie's ambition and personality. Qu Yuan was my country's first romantic poet and created Chinese romantic literature. From then on, Sao-style poetry appeared, represented by "Li Sao". Qu Yuan was a native of Chu, so he also called this style of poetry "Chu Ci". For example, "The road is long and long, and I will search up and down" is such a rhyming style of poetry.
Sima Qian's "Historical Records" is based on recording historical facts. In addition, his writing is lifelike, so it also has a very high literary value. It is not only a powerful basis for historians to study history, but also has a profound influence in the literary world. It has a very high status and has played a very good guiding role in the character image and character description of later generations of literature. Therefore, Lu Xun said that it is a rhymeless Li Sao, which shows that "Historical Records" has been mentioned to a quite high status.