Nuclear DNA contents of developing sperm were estimated for 17 species of bryophytes by cytophotometry in squash preparations of antheridia after Feulgen staining. Genome sizes are in the lower end of the range for land plants. Two homwort C‐values have the lowest recorded for bryophytes at 0.17 and 0.26 pg DNA per nucleus. In liverworts, C‐values range from 0.49 pg inBlasia pusillato 4.05 pg inPellia epiphylla, while moss genome sizes are less variable, ranging from 0.38 pg inTakakia ceratophyllato 0.92 pg inAtrichum oerstedianum.DNA content is not correlated with chromosome number in these bryophytes, but sperm cell size and cellular complexity are directly related to C‐value. Structural variations in the locomotory apparatus are viewed as evolutionary modifications associated with changes in genomic complexity, with a generalized increase in complexity of the motile assemblage accompanying increases in DNA content. Nuclear DNA values are not as variable in bryophytes as they are in pteridophytes and seed plants. We suggest that in plants producing biflagellated gametes, lower DNA contents afford a selective advantage. Comparisons with plants that produce multiflagellated or pollen‐dispersed sperm indicate operation of a nucleotypic effect in archegoniates with biflagellated sperm. This effect may be on sperm cell functioning, which in turn influences reproductive success.