An account is given of the spore, germination, vegetative features, and reproductive organs of the gametophyte of Blechnum nudum. The species is unlike other Blechnum spp. so far described in having a green spore, a prothallus without hairs, and an early formation of cells in a third dimension. The apical cell develops from the terminal cell of the short filament, chloroplasts are present in the rhizoids, and the mature prothallus is cordate with a slightly depressed sinus and an irregular margin. At one year the prothallus becomes elongated with a thick midrib and slightly ruffled wings. The antheridium is elongated and has a disk or occasionally columnar shaped basal cell, a ring cell, and an asymmetrical cap cell. Some antheridia on the cushion region become very large. Nuclear divisions in the development of the antheridium are described in detail. The archegonium has a squat appearance, develops in the usual manner, and has a short, rather straight neck.