Thallus flat or with some flat or flattened parts:
Flat part of thallus with conspicuous mid-rib extending to the apical end 2
Thallus without such mid-rib 6
Thallus alternating or pseudodichotomously branched, with narrow blade “rim” around mid-rib Membranoptera alata
Thallus not branched in this way 3
Thallus with lobes or proliferations from edge (which grow to new leaves), “oak leaf” like Phycodrys rubens
Thallus always with smooth edge 4
Large, elongated blades, with conspicuous and macroscopic side nerves Delesseria sanguinea
Relatively small blades lacking macroscopic side nerves, new blades grow from mid rib 5
Microscopic side nerves like ”veins” formed by elongated cells in rows from mid rib Apoglossum ruscifolium
No such clear microscopic veins Hypoglossum hypoglossoides
Thallus with nerves (polystromatic thickenings of blade) or veins but not forming a mid-rib to the apical end of thallus 7
Thallus lacking nerves or veins 8
Several nerves proliferating the basal parts of a lobed blade, with additional veins Cryptopleura ramosa
Thallus with a stipe which continues as mid-rib some distance up on a lobed, otherwise monostromatic blade Haraldiophyllum bonnemaisonii
Thallus with blade formed parts and a round and long stipe relative to blade length 9
Thallus with flattened or blade formed parts, lacking or with a small round stipe 12
Small (to 3 cm) and often occurring in groups, blade irregularly lobed or dicochomuosly branched, rare Erythrodermis traillii
Thallus normally larger than 3 cm and with relatively long stipe, and with dichotomously branched or lobed blades 10
Flat part of thallus repeatedly (< 3 times) dichotomously divided,
stipitate blades may branch off from stipe Phyllophora pseudoceranoïdes
Flat part irregularly lobed or dichotomously divided to 3 times, new blades can grow from stipe or blades 11
Basal stipe normally shorter than primary leaf, branching only in lower part, adventitious leaves without stipe Coccotylus truncatus
Branching with stipitate leaves from all parts of plant, often apically Coccotylus brodiei
Thallus or axes flat and with some kind of branching pattern 13
Thallus is plain leaf or blade-formed or like a blade with lobes or splits 30
Branches like proliferations or new blades growing from the edge of a relatively broad blade and in the same plane as the blade 14
Not branching in this way 16
Thallus hollow, main axis like a broad flat blade narrowing to the top, first order side branches broad and with strong constrictions at the base, making them look like blades growing from the edge Lomentaria orcadensis
Thallus not hollow 15
Blade can be divided in 2-3 (4) lobed sections, and new blades grow from edge of the old blade Palmaria palmata
Thallus more or less dichotomously divided, numerous thin proliferations from edge, North Norway Fimbrifolium dichotomum
Regular feather branching with opposite branches, one of the pair often shorter than the other in an alternating way, stiff and with a broad rounded mid axis Ptilota gunneri
Not consistent opposite branching 17
Consistent alternate or unilateral branching in last orders of branching 18
Irregular or dichotomous branching 19
Main axes with inconspicuous mid rib and alternately branched, side branches end in 2-3 small “teeth” Odonthalia dentata
Main axis with alternating side branches, where those of the last order are placed unilaterally (like a comb) Plocamium lyngbyanum
Main axes relatively narrow, side branches with constrictions at base, side branches can be in one plane or not Lomentaria clavellosa
Main axis like a broad flat blade narrowing to the top, first order side branches broad and with strong constrictions at the base, making them look like blades growing from the edge Lomentaria orcadensis
Bright red, main axes and side branches flattened, branches of 1-2 (3) orders, placed opposite or irregular Gelidium spinosum
Often brownish red, more or less flattened, cartilaginous, branches stunted and placed irregularly 24
Thallus with a round attachment disc Osmundea oederi
Thallus with stolons (relatively rare) Osmundea pinnatifida
Relatively big (up to 10-15 cm) and strongly dividedin wide branches or lobes, with a frilled edge when fertile Metacallophyllis laciniata
Relatively small (up to 5 cm), strongly divided in many narrow branches, often on hapteron of kelp Euthora cristata
Dichotomous branching, some species also with lobes or new blades or prolifierations from edge of blades, in the same plane as the blade 27
Dichotomous branching, thallus not with new blades or proliferations from blade edge 28
Blades elongated and more or less dichotomously divided, numerous thin proliferations from edge, North Norway Fimbrifolium dichotomum
Short stipe, long ”crispy” elongated blades with parallel sides and divided in 2 or 3 lobes, with new blades growing from the to Phyllophora crispa
Short stipe (may lack), small, thin thallus irregularly dichotomously divided, sheltered bays Rhodophyllis divaricata
Bushy in upper part, thallus narrowing to basal parts, occurring mainly in intertidal 29
When fertile with small papilla or “warts” in upper part Mastocarpus stellatus
Without papilla on blades, may iridize in sun Chondrus crispus
Thallus is plain leaf or blade-formed or with lobes:
New blades or prolifierations from edge of blade, in the same plane as the blade 31
Thallus flat or blade-formed without proliferations 33
New blades growing only from top of old blades. Short stipe, long ”crispy” elongated blades with parallel sides and divided in 2 or 3 lobes often carrying new blades Phyllophora crispa
New blades or proliferations from edge of all parts of the blade 32
Blade can be divided in 2-3(4) lobed sections, and new blades grow from edge of the old blade Palmaria palmata
Thallus deeply lobed or more or less dichotomously divided, numerous thin proliferations from edge, North Norway Fimbrifolium dichotomum
Monostromatic blade, irregularly dichotomously divided often in wedge-shaped lobes, elongated polygonic cells, blade with elongated sori when fertile Nitophyllum punctatum
Blades rounded or irregularly lobed, small and rounded surface cells 35
Monostromatic leaves to 4 cm, small, rounded cells (3-8 um), sublittoral and always several individuals together Porphyropsis coccinea
Thallus normally >4 cm, vegetative cells grouped 2 or 4 together Porphyra*, Pyropia, Neopyropia, Wildemania
Eight species recorded in Norway. Two intertidal species* are common and easy to identify: P. umbilicalis (with attachment point on the lamina) and P. linearis (short stipe and long and narrow lamina)
Dark red blades, to 40 cm, often several from the same attachment disc. Medulla consists of elongated filaments Dilsea carnosa
Dark red and rounded blades, to around 10 cm, North Norway. A short stipe from a notch in the blade Turnerella pennyi
Short stipe (may lack), thallus up to 2-3 cm, thin and irregularly dichotomously divided Rhodophyllis divaricata
Thallus with lobes or insertions but not consistently dichotomously divided 40
Thallus relatively big and divided in or lobes 42
Thallus relatively small and divided in lobes 41
Small (to 2 cm) and often occurring in groups, thallus with a conspicuous stipe, blade with irregular or lobed outline, rare Erythrodermis traillii
Relatively small (up to 5 cm), strongly divided in many narrow branches or lobes, often on hapteron of kelp Euthora cristata
Relatively big (up to 10-15 cm) and strongly divided in wide lobes, with a frilled edge when fertile Metacallophyllis laciniata
Elongated blade divided in long lobes apically, rare Halarachnion ligulatum
