Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Martĭgĕna, ae, comm. [Mars-gigno], Mars-born, begotten by Mars (poet.): Martigenae … Romulus Iliades, Iliadesque Remus, Ov. Am. 3, 4, 39: Martigena Quirinus, id. F. 1, 199: vulgus, i. e. martial, Sil 16, 533.