Sun Tai chi is the newest of the 5 main Tai Chi styles. It was created by Sun Lutang in the early 1900s. Sun Lutang was already proficient in the other two Chinese internal martial arts styles of Xing Yi and Bagua. He learned Wu(Hao) style Tai Chi from Hao Wei Zhang. He also studied the Yang style with Yang Cheng Fu. The Sun style is different from Yang and Chen styles. Only rarely do the legs separate farther than shoulder width. The original form created by Sun Lutang was the Sun 97. It has the same pattern as the Wu long form which is patterned after the Yang 108 form.
The Sun 38 form was put together in Beijing by a University Professor, Li Deyin. The movements are taken directly from the original Sun 97 form. Like the Yang 24, it is learned in a much shorter period of time than the long form and can be a stepping stone to the longer form. The 38 form is not an "easier" form, it is just shorter.
Below is a link to my page which has the list of movements and a video of the Sun 38 form.
38 from list and video