Abstract: A new species of Porphyra has recently been discovered from the Fukien coast. The new alga, Porphyra haitanensis T. J. Chang et B. F. Cheng, sp. nov., is the principal component of the Porphyra growths on the cultivated rocks in the upper littoral region in Haitan Island (Pingtan District), Fukien, the place where the special method of employing lime water on rocks in Porphyra cultivation was initiated some 150 years ago. A description of the new species are as follows: Thalli generally 12–18 cm, sometimes over 28 cm in height; blades lanceolate, subovate or elongated subovate, shortly but conspicuously stiped, generally with broad cordate base and some with rounded or cuneate ones, marginal portions sometimes slightly undulate, membranaceous, the middle portions 65–95 μ and that near the base up to 110μ in thickness; the margin with microscopic, one to three-celled teeth, but in the rather mature thalli the dentate character generally limited to the basal parts near the holdfast, the upper parts becoming more or less entire and with looser marginal cells; generally monostromatic, but distromatic portions constantly present; vegetative cells 15–22 μ broad, rectangular in sectional view, 35–50 μ in height excluding the gelatinous sheath, generally with a single, axial, stellate chromatophore, but sometimes with two chromatophores; mostly dioecious, sometimes monoecious, in the latter case, spermatangial portion and sporocarpial portion found on the same frond delimited from each other by a straight, curved or crooked line; each spermatangium composed of 128 or 256 spermatia arranged according to the formulae: ♂ A4B4C8 or ♂ A4B4C16; each sporocarp composed of 16 and in lesser cases of 32 carpospores arranged according to the formulae: ♀ A2B2C4 or ♀A2B4C4; the colour of the specimens dark greenish purple, with brownish tinge when fresh, becoming more greenish when dried, turning to dark purple a few months later. The type specimen, M 592070, was collected on a rock in the upper littoral zone, Dung Au, Pingtan District, Fukien Province on 25 Feb., 1959, deposited in the Herbarium of the Institute of Oceanology, Academia Sinica. The species is widely distributed along the Fukien coast. The Fukien porphyra product, estimated 12000 tons, fresh weight, in 1958, is principally composed of the present species, with P. dentata Kjellm., P. suborbiculata Kjellm. and P. crispata Kjellm. as the minor components. The growing season of the present species is from October to March of the next year. During this period the porphyra is havested once in every 15–20 days at iow tide by plucking down the upper parts of the thalli and letting the lower parts remain unharmed for further growth. There may be six to nine harvestings in a single growing season. Systematic position of the new species: Porphyra haitanensis T. J. Chang et B. F. Zheng belongs to the subgenus Euporphyra Rosenvinge and to the section Dentata Tseng et T. J. Chang. It is rather nearly related to P. dentata Kjellm., but is differentiated by (1) the presence of monoecious thalli, (2) the presence of the distromatic and bichromatophored characters, though only in parts, (3) the different modes of division of both spermtangia and sporocarps with different numbers of reproductive cells and (4) the greater thickness and the dark greenish purple colour of the thalli.