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Plant materials with different ploidy levels from a series of reciprocal crosses between a wild Cucumis species (Cucumis hystrix Chakr., 2n = 2x = 24) and cucumber (Cucumis sativus L., 2n = 2x = 14) were used to investigate reciprocal differences in morphology, fertility, and DNA characteristics. Diameter of the stem, length of the petiole, and shape and size of the leaves of the hybrids were intermediate when compared with their parents. The length of the internode of the main stem showed maternal transmission in all hybrids, but the branching number and appearance of the first female flower showed paternal transmission. The differences in fertility of reciprocal plants were significant. When C. hystrix was used as the female parent, the diploid (2n = 2x = 19) hybrids set fruit without seeds, whereas the amphidiploid (2n = 4x = 38) plants produced fruits with viable seeds. However, when cucumber was used as the female parent, both tetraploid and diploid hybrid plants were highly sterile and did not set fruits. To further investigate variation in hybrid genomes, 21 arbitrary primers were used for random amplified polymorphic DNA analysis. Reciprocal differences were detected for 15 primers. The banding patterns were different among the four types of hybrids, but there was no significant difference in the total and (or) average numbers of bands observed. We suggest that the differences in random amplified polymorphic DNA banding patterns of the hybrids are probably related to the paternal- and (or) maternal-transmitted morphological characteristics in the reciprocal cross. [ABSTRACT FROM AUTHOR]