Any problems in this little poem are exegetical – there are no significant variants:
Quae legis causa nupsit tibi Laelia, Quinte,
uxorem potes hanc dicere legitimam.
As a punch-line, the pentameter, particularly the last word, seems rather flat. I suspect a pseudo-etymological pun: as a wife, Laelia is legitima, quia legem timet. She is not only a lawful wife, but a law-fearing wife, a wife only for fear of the law.
Of course, legitimus is no more a compound of timeo than finitimus or ultimus. The only Latin word of similar formation (lex + a verb that would govern it in a complete sentence) is Plautus’ legerupa. On the other hand, the prevalence of disyllabic pentameter-endings in Martial might help the reader to divide legitimam into its two pseudo-components.
