"The S.O. Has Only Got One Frond" is a popular drinking song in Headquarters, written by an unknown agent. While nobody remembers who wrote it or when, it's a common choice for disgruntled agents with strong beer and decent singing voices. "It [is] one of those songs that [has] the much-prized combination of catchiness, hardly ever being sung entirely sober, and being able to insult Upstairs without anyone minding overmuch."
The song references members of the Board of Department Heads one after another; where the content lies from good-natured ribbing to outright sedition depends on who's singing and how drunk/disgruntled/both they are. While the lyrics can vary, such as the Flower with "no fronds at all" changing depending on the singer, the general idea remains the same. It isn't known how Doctor Fitzgerald, a human doctor, fits into the song.
Like its World One counterpart, it can probably be assumed to use the same general tune as the "Colonel Bogey March." It might or might not have been updated with the death of the Clover and his replacement by the Fern.