As others have said, men certainly do write romance.
I'd like to point out, though, that not all male genre Romance authors write under female pen names.
Ken Casper currently writes for Harlequin under his own name. That said, his earlier titles were published under K.N. Casper, which I don't think sounds very feminine either, but does hide the fact he's male.
Another one is Wayne Jordan who writes for Harlequin's Kimani Press.
I'm sure there are others but those are two who come immediately to mind. Probably because I've seen both of them at RWA conferences. In a sea of women, the poor fellas kinda stood out.
