The Martha Kent story is actually more complicated than you might think because Clark's parents weren't originally called Jonathan and Martha (which Wiki comics doesn't make clear).
From Wikipedia <additions by me>
Originally "Mary Kent" was the only parent given a name <in 1939>. The Kents' first names vary in stories from the 1940s. A 1942 Superman novel, The Adventures of Superman by George Lowther, gave the names "Eben and Sarah Kent", which were also used in the Adventures of Superman television series, but the first extensive retelling of Superman's origin in Superman #53 (July-August 1948, billed inaccurately as a "10th Anniversary Issue!") names them "John and Mary Kent". <cut a few lines>
This story also establishes that "Clark" is Mary Kent's maiden name. Mary and John Kent (in that order) die of natural causes as "Clark grew to manhood" <cut a few lines>
Pa Kent is first named Jonathan in Adventure Comics #149 (1950). Ma Kent is first named Marthe in Superboy #12 (1951) and Martha in subsequent appearances. Later stories, after the early 1960s introduction of DC's Multiverse system, declare that the early version of the Kents are named "John and Mary Kent" and live on the world of "Earth-Two", home of the Golden Age DC superheroes, while the more modern Jonathan and Martha Kent live on the world of "Earth-One", home of the Silver Age DC superheroes.
So in fact the original Martha was in Batman (from 1939 onwards), not Superman!
Now if we could have only got the 10th Doctor and Martha Jones in there too...
