Just like most kelps, Saccharina latissima has blades (lamina), stipes and holdfasts which attach to substrates. The sporophytes of Saccharina latissima have a rich medium brown color, a long undivided frond without a midrib and a profusely branched holdfast. Mucilage ducts are absent from stipe; the blade often has two rows of bullations formed in two longitudinal rows parallel to the central axis. The frond of Saccharina latissima has a distinctive frilly undulating margin. The stipe of Saccharina latissima may be up to 50 cm long.

Carbohydrates stored as mannitol and laminarin are used to support the growth of new tissues. Sieve cells are common and usually penetrate the cell wall. Pyrenoids are used for storage and occur within the double membrane of the chloroplast.

Saccharina latissima contains various pigments including chlorophylls a and c (c1, c2, c3), beta carotene, fucoxanthin, and neofucoxanthin, as well as other cartenoids.

Tissue differentiation can be seen in the cross section of Saccharina latissima clearly: an epidermis, an outer cortex, inner cortex and a central medulla that contains trumpet hyphae (sieve cell used for conduction).

Reference:

Dawes, C. J. 1997. Marine Botany

Wikipedia (http://en.wikipedia.org/wiki/Wiki)