Thallus with round (or rounded) axis or axes in cross section, not flat in any part:
Oppositely branched, common in the littoral Corallina officinalis
Dichotomously branched, relatively rare Jania rubens
Small (normally <1 cm), irregularly branched with strong constrictions at irregular intervals, dark red (blackish) thalli, turf-forming in upper intertidal in shady places Catenella caespitosa
Thallus different 4
Thallus hollow or partly hollow (often obscure in small/young individuals) or with cross walls (septa) at irregular intervals 5
Thallus not hollow 10
Occurring only in intertidal and mainly with 1rst order branches 6
Mainly sublittoral and normally with more than 1rst order branches (except young individuals) 7
Short main axis and long side branches, spring/summer in the intertidal, bleached/yellow during summer Dumontia contorta
All year around, very variable in morphology but relativly firm thallus, only in North Norway Devaleraea ramentacea
Thallus with opposite branches or branches set in whorls (may be obscure in young individuals) 8
Thallus not with consistently opposite branches or branches set in whorls 9
Axes with cross walls at regular intervals, which carry opposite or whorls of branches Chylocladia verticillata
Axes with very strong constrictions, short side branches and limited to the intertidal of southwest Norway Lomentaria articulata
Clearly hollow in all parts, branches can be in one plane or not, axes often with short branches between larger ones, branches with constrictions at the base Lomentaria clavellosa
Axes hollow in lower parts, main axis with irregular and repeated branching, some branches gradually narrowing like tendrils Cystoclonium purpureum
Thallus not hollow:
Thallus pluriseriate (except young thalli), brownish red, thin “hair”, forming felt-like patches intertidally in wave-exposed sites during spring Bangia fuscopurpurea
Uniseriate and normally microscopic, star formed plastid Erythrotrichia carnea
Thallus uniseriate, but axes may partly be covered with rhizoidal cortex cells 42
Thallus pluriseriate but may have uniseriate short side branches with determined growth 13
Thallus uniseriate with large cells, visible to the naked eye Griffithsia corallinoides
Thallus pluriseriate 15
Repeatedly dichotomously branched, thick axes (around 2 mm in diameter) 16
Repeatedly pseudodichotomously branched, axes < 2 mm 32
(E.g. some Vertebrata, Polysiphonia, Ceramium)
Thallus dark red, soft, gelatinous, sparsely dichotomously branched, wave-exposed intertidal in summer Nemalion elminthoides
Firm and cartilaginous axes 17
Thallus with numerous small uniseriate side branches in all parts of thallus 19
Thallus not with numerous uniseriate side branches (or present only in apics), but last order of branches may be uniseriate 22
Axes divided in segments, which may be obscured by cortex in lower parts 20
Axes covered by cortex in all parts, sections normally not visible, present in Skagerrak Dasya baillouviana
Main axes with cortex in basal parts 21
Axes without cortex, short uniseriate side branches set in a spiral Vertebrata byssoides
Short uniseriate side branches, one per segment Dasysiphonia japonica
Uniseriate side branches with a pluriseriate basal part, formed every 2-3 segments, branches in one plane Heterosiphonia plumosa
Some type of consistent regular branching present in all or parts of thallus (alternate, opposite or unilateral) 24
Branching not consistently regular in any part of thallus 29
Narrow, flattend axes, main axis with more or less alternating side branches, last orders branches placed unilaterally (like a comb) Plocamium lyngbyanum
Regular opposite or alternate branching present 25
Branching consistently alternating in all parts of thallus, axes divided in segments without cortex cells Symphyocladiella parasitica
Branching opposite or alternating, axes not divided in segments without cortex cells 26
Oppositely branched, one of the branches may be shorter than the other but not in an alternating way, last order of branches uniseriate Plumaria plumosa
Last order branches pluriseriate 27
Last order branches short and oppositely or alternately placed but not appearing feather-branched, if fertile cystocarps or spermatangia are placed opposite to a short side branch Bonnemaisonia asparagoides
Feather-branched with a stiff and with a broad mid axis 28
All side branches with feather branching, oppositely branched where one branch may be shorter than the other in an alternating way Ptilota gunneri
Oppositely branched where the shorter branch of a pair does not carry side branches and appear thorn-like. Northern distribution Ptilota serrata
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 30
Thallus with a round attachment disc Osmundea oederi
Thallus with stolons (relatively rare) Osmundea pinnatifida
Thallus clearly segmented or striped, at least visible in young parts 32
Thallus completely covered with cortex cells, axes do not appear segmented or striped 35
Segments formed by cells of equal height (at least 4), can be covered by elongated cortex cells. See key (several genera) 33
Axes appear more or less striped. Thallus with large often round central cells, with a ”girdle” of cortex cells in the junction, or more or less covered by cortex, tip ending in two branches curled towards each other.
See key for Ceramium 34
Key for Polysiphonia, Melanothamnus, Savoiea, Leptosiphonia, Carradoriella and Vertebrata.
Not included: P. hemisphaerica (rare southern species, recorded west to Lindesnes)
| Species | No periaxial cells or arrangem. of plastids | Cortex cells | Thallus habit/ Branching |
Habitat |
|---|---|---|---|---|
| Vertebrata byssoides | 7 | Lacking | Short uniseriate side branches set in a spiral | Sublittoral |
| Vertebrata lanosa | 12-24 | Lacking | Bushy thallus | On Asco-phyllum |
| Vertebrata fucoides | 12-16 | Lacking or some near the base | Several main axes, morphology varies | Intertidal, subtidal |
| Vertebrata nigra | 9-13 (spiral formed) | Lacking | Strongly branched, many short side shots set spirally | Intertidal, subtidal |
| Savoiea arctica | (4)-6-(7) | Lacking | To 10-15 cm, dark red, long segments in middle part | North Norway, subtidal (deep) |
| Carradoriella elongata | 4 | With cortex almost to the apexes | Relatively thick main axes with thinner end axes (reduced to main axes in autumn) | Subtidal |
| Polysiphonia stricta | 4 | Lacking | Thin branches twisted round each other. Rhizoids with connection to periaxial cell | Intertidal, subtidal |
| Leptosiphonia fibrillosa | 4 | Cortex at the base | Soft, thin branches Rhizoids not connected to periaxial cell | Intertidal, subtidal |
| Leptosiphonia brodiei | 6-8 | Main axes with cortex | Bundles of short branches | Intertidal, wave-exposed |
| Melanothamnus harveyi | 4 Plastids placed innermost, towards the central cell |
Main axes covered with cortex at the base | Main axes strongly branched to thinner side branches | Upper subtidal, often epiphyte |
Key for Ceramium.
Ceramium botryocarpum and C. siliquosum are not included (probably rare).
| Species | Cortical bands with spines | Cortex cell cover | No of periaxial cells | Habitat, branching |
|---|---|---|---|---|
| Ceramium shuttleworthianum | Yes, basal cell can be longitudinal divided | In cortical bands, and also forming characteristic “thorns” | – | Small, wave-exposed intertidal, strongly inrolled apics |
| Ceramium deslongchampsii | No | Confined to cortical bands | 5 | Apics slightly incurved. Tetraspor. naked. Rare |
| Ceramium sungminbooi | No | Cortical bands sparse, only at nodes | 5 | Apics slightly incurved |
| Ceramium diaphanum | No | Strongly confined to cortical bands, often collar-like | 6-7 | Inrolled apics, open (>60°) branching |
| Ceramium “strictum” Name not valid |
No | Confined to cortical bands | 6-7 | Occurs in relative brackish water (Skagerrak, Hardangerfjord). Thin axes |
| Ceramium virgatum | No | Completely covered | 6-8 | Few adventitious branches, strongly irregular branching every 4-30 nodes |
| Ceramium secundatum | No | Normally completely covered | 7-9 | Strongly inrolled apics,adventitious branches common, relatively regular branching every 8-15 nodes, kidney-formed gland cells betw. cortex cells |
| Ceramium pallidum | No | Normally not complete | 6-7 | Inrolled apics, often epiphyte, branch every 5-12 nodes, |
Occasional conspicuous hook-formed branches Bonnemaisonia hamifera (n)
Never with hook-formed branches 36
Thallus with clear main axes, and always attached 37
Thallus not with clear main axes, normally loose-laying 40
Short main axis with long 1rst order side branches, intertidal in spring Dumontia contorta
Long main axes, branches of more than 1rst order 38
Cross section of axes shows a round central cell 39
Not a round central cell, main axis with irregular and repeated branching, some branches gradually narrowing like tendrils Cystoclonium purpureum
Main axes with side brances often in “bundles”, but very variable in habit Rhodomela confervoides
Main axes densely set with short branches, often epiphytic on stipes of Laminaria hyperborea Rhodomela lycopodioides
Not with clear main axes, Stiff and thin branches, almost black, often loose-laying but also growing attached in intertidal Ahnfeltia plicata
Cartilaginous, somewhat flexible branches, diameter 1-2 mm 41
Sparsely and irregularly branched, in warm bays Gracilaria gracilis
Like the former but more brownish in colour, introduced and spreading in Skagerrak Agarophyta vermiculophylla
Thallus uniseriate, but axes may partly be covered with rhizoidal cortex (note that this is a large group with many species which are difficult to identify):
Thallus with small pigmentless gland cells visible in “corners” between cells Bonnemaisonia hamifera (2n)
Thallus without gland cells 44
Plastids with large and conspicuous pyrenoids Rhodothamniella floridula
Without such pyrenoids and small thalli (< 1cm), several genera: Acrochaetium, Colaconema, Rhodochorton, Meiodiscus, Rubrointrusa
Thallus with dichotomous branching and large cells (visible by the naked eye) Griffithsia corallinoides
Thallus with thin axes (relatively small cells) and regular branching:
Several genera, e.g. Callithamnion, Antithamnion, Aglaothamnion, Gaillona*. Consult a special Ceramiales key
* Gaillona seposita: Characteristic alga in wave-exposed intertidal; small, brownish red, very densely branched and bushy
