More, including expanded commentary and peer review at http://libromancersapprentice.blogspot.com/2013/07/herland-and-gender-expression.html
Herland celebrates women, but only women of a very narrow, cisgendered scope that ignores the complexities of gender. The women all possess the vaulted traits of intelligence, wisdom, strength, and physical female perfection. They are also all the ultimate mothers, all desiring and cherishing children. These women are strongly gendered within this.
Women across time, regardless of their origins, vary in their conformity to gender norms. At the time that Herland was written, "Boston marriage" existed in the vernacular, encompassing a range of alternative relationships and gender expressions. Women who lacked attraction to men, women who lived independent from men, women who felt like they were in the wrong body, women who simply did not fit the "female" mold. These were common enough to have a name rather than existing simply as an oddity.
The initial generations of Herland reproduced without controls, not until the more recent generations did they actively work to regulate their population. Allowing for the many generations of rapid population growth and within the constraints of parthenogenesis over time they could viably have a wide genetic spread across their population.
It is unknown what really defines gender, be it genetics or socialization. Here we have both factors even if we have a single gender instead of a binary gender system. Not only that, but physical gender expression does not always match the chromosome pairs. Why does Herland have no intersex or XX male children? Why are all of the women gendered as mothers? Even without a male gender there is still room for variance in gender expression and identity. In our world non-binary genders do not necessarily mirror the opposing binary genders. In a utopian culture of intellect and wisdom, would they not accept a wider range of gender expression than that of an ultimate motherhood?
cisgender - someone who's percieved gender matches their birth gender <http://en.wikipedia.org/wiki/Cisgender>
Boston marriage - two women living together independent of men during the late 19th and early 20th century, some in lesbian relationships, some not <http://en.wikipedia.org/wiki/Boston_marriage>
Parthenogenesis - a form of asexual reproduction, also known as "virgin birth" <http://en.wikipedia.org/wiki/Parthenogenesis>
Intersex - posessing variations in sex characteristics that do not allow for clear gender classification <http://en.wikipedia.org/wiki/Intersex>
XX male - men with 'female' chromosomal pairs <http://www.ncbi.nlm.nih.gov/pubmed/16556678>
Gilman, Charlotte Perkins. Herland. Retrieved from http://www.gutenberg.org/ebooks/32