Seed dormancy is a block to the completion of germination of an intact viable seed under favorable conditions and is an adaptive and agronomically important trait. Thus, elucidating conserved features of dormancy mechanisms is of great interest. The worldwide-distributed genus Lepidium (Brassicaceae) is well suited for cross-species comparisons investigating the origin of common or specific early-life-history traits. We show here that homologs of the seed dormancy-specific gene DELAY OF GERMINATION1 (DOG1) from Arabidopsis (Arabidopsis thaliana) are widespread in the genus Lepidium. The highly dormant Lepidium papillosum is a polyploid species and possesses multiple structurally diversified DOG1 genes (LepaDOG1), some being expressed in seeds. We used the largely elongated and well-structured infructescence of L. papillosum for studying primary dormancy induction during seed development and maturation with high temporal resolution. Using simultaneous germination assays and marker protein expression detection, we show that LepaDOG1 proteins are expressed in seeds during maturation prior to dormancy induction. Accumulation of LepaDOG1 takes place in seeds that gain premature germinability before and during the seed-filling stage and declines during the late maturation and desiccation phase when dormancy is induced. These analyses of the Lepidium DOG1 genes and their protein expression patterns highlight similarities and species-specific differences of primary dormancy induction mechanism(s) in the Brassicaceae.