Ptilium crista-castrensis dioicous pleurocarpous moss with ascendent to erect stem; mature gametangia are situated on parts of shoots of the second year, and sporophytes occur on parts of shoots of the third year. Female gametangia-bearing plants are 20% larger on average than male gametangia-bearing plants, while sterile plants of both genders do not differ in size from each others. At the same time, the percent of sterile plants within male populations is smaller than in female populations. In most parts of Russia the proportion of male and female collections in herbaria is close to equal; however, in the severe climate of Arctic and Yakutia, male plants are very rare and female plants prevail.