The stamen (plural stamina or stamens, from Latin stamen meaning ""thread of the warp"") is the male reproductive organ of a flower. Each stamen generally has a stalk called the filament (from Latin filum, meaning ""thread""), and, on top of the filament, an anther (from Ancient Greek anthera, feminine of antheros ""flowery,"" from anthos ""flower""), and pollen sacs, called microsporangia. The development of the microsporangia and the contained haploid gametophytes, is closely comparable with that of the microsporangia in gymnosperms or heterosporous ferns.