DISCLAIMER: These keys and species identities are provided for informational purposes only. We can take no responsibility for any consequences of misinterpreted information presented here. Always consult your local algae specialist if you have questions.



The 17 genera listed in this key represent about 65 % of the brown algal genera in the Hawaiian Islands. As with the green algal key, some key lines end in a specific name which indicates that there is only one species in the genus or that a certain species is different from the remainder in that genus and can be isolated by itself. The number in parentheses that follows genus names is the number of species recognized for that genus at this time in Hawai’i. Isabella Abbott, January 1997.

1 Plants having flattened to cylindrical stem-like portion 2
1 Plants without stem-like structure 3
2 When mature, plant divided into clear holdfast, "stem" and "leaves"; plant without spines more than 4 mm long Sargassum (3 spp)
2 When mature, plant divided into a cone-shaped structure in which stem is surrounded radially by disk-shaped "leaves"; spiney, hard, leafless projections or branches more than 10 mm long; common Turbinaria ornata
3 Plants divided dichotomously from base to apex or more than upper half of plant dichotomous 4
3 Plants not divided dichotomously, fronds bladelike, or irregularly branched 5
4 Fronds flattened, ribbon-like with a marked midrib; usually an olive-brown Dictyopteris (3 spp)
4 Fronds flattened, without a midrib; usually golden; if subtidal some species iridescent Dictyota (3 spp)
5 Plants widened blades; margins may be torn or irregular 6
5 Plants not bladelike 10
6 Fronds fan-like or ear-like, relatively thick, with concentric lines containing calcium carbonate; terminal margin inrolled on inner or ventral surface Padina (7spp)
6 Fronds not fan-like, relatively thin, lacking calcium carbonate lines, without inrolled margin 7
7 Blades erect, frequently torn along lateral margins 8
7 Blades tightly adherent by numerous rhizoids or attached loosely as stiffened sheets with radial lines; in cross-section with a single medullary layer surrounded by several cortical layers on each side Lobophora variegata
8 Blade smooth, plants usually weakly attached; not iridescent 9
8 Blades not smooth, roughened by arching lines; plants usually tenaciously attached, iridescent when alive Stypopodium hawaiiensis
9 Blades sickle-shaped or broadened about 2/3 of way to top, becoming narrower at upper margin, usually found on cobbled bottom or rough shores Endarachne binghamiae
9 Blades strap-shaped, with proliferations along margins in one plane, sometimes ruffled; subtidal in isolated locations Spatoglossum macrodontum
10 Plants erect or matted, irregularly branched or filamentous 11
10 Plants not erect or matted, not branched or filamentous 12
11 Fronds erect or matted; irregularly divided branches with forked tips; cross-section pseudoparenchymatous Chnoospora (2 spp)
11 Fronds erect, filamentous 15
12 Plants golden-brown hollow sacs, epiphytic or on rocks, mid-intertidal Colpomenia sinuosa
12 Plants not sac-like 13
13 Plants branched tubes, erect branches soft and stringy or matted and decumbent Rosenvingea (2 spp)
13 Plants not branched tubes 14
14 Plants thick dark brown to blackish high intertidal "tar spots" on rough coasts Ralfsia expansa
14 Plants thick olive-brown nets, or crustose with conspicuous irregular holes in surface Hydroclathrus clathratus
15 Filaments stiffly branched or unbranched; on rock or epiphytic; mature axes bearing laterals modified in characteristic shapes; plants multicellular below apical regions; usually dark brown Sphacelaria (3 spp)
15 Filaments generally epiphytic without definite shape; lacking modified terminal ends of axes; not multicellular below; usually olive to golden brown


16 Plants short, lax, usually epiphytic; intercalary meristems basal to long, unbranched filaments distally terminating in colorless hair Feldmannia (2 spp)
16 Plants arranged in rope-like strands or fluffy, much-branched tufts, intercalary meristems scattered throughout axes and major branches; terminal colorless hairs usually absent Hincksia (3 spp)

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