Protologue Description: Fucus vesiculosus forma gracillima Collins. Among Spartina, etc., on muddy bank between tide-marks, Eastham, Massachusetts, September, 1888. No. 578, With oospores. A very slender form, without vesicles, and with receptacles linear to filiform. It is probably only a growth form, but unlike most of the dwarf forms of this species, it fruits freely.