Key to Common Genera and Species

KEY TO COMMON GENERA AND SPECIES

OF HAWAIIAN PHAEOPHYTA

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
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)

Key to species of Sargassum

1 / Primary branches ("stem") smooth, without projections or spines / 2
1 / Primary branches ("stem") with spinous projections / S. polyphyllum
2 / Primary branches flattened at base; receptacles spiney, vesicles ("floats") on flattened petioles sometimes common / S. echinocarpum
2 / Primary branches flattened or compressed upwards from base to second or third secondary branch; receptacles smooth and finger-like; vesicles ("floats") on cylindrical petioles / S. obtusifolium
Sargassum polyphyllum Collector: P. Vroom #2-023

Key to the species of Dictyopteris

1 / Fronds very similar to Dictyota species, but nearly wholly prostrate and with midrib; branching irregularly dichotomous / D. repens
1 / Fronds not similar to Dictyota (wider, taller, coarser), not prostrate; with numerous apical cells / 2
2 / With veinlets visible to naked eye, forming acute angles to the midrib; sporangia or gametangia in linear patches parallel to midrib; blade mostly distromatic from margin to midrib / D. plagiogramma
2 / Veinlets microscopic and faint; sporangia or gametangia in rows starting at midrib and arching downward to lateral margins; blade monostromatic for up to 15 cells from margin, then di-polystromatic to midrib / D. australis
Dictyopteris australisCollector: M. Yoshizaki
Turbinaria ornataCollector: E. Goergen, Sandy Beach,2/22/99

Key to the species of Dictyota

1 / Plants dark chocolate brown, fronds tightly to loosely spiralled (twisted) axes up to 3 mm in diam., terminal dichotomous division about 1 mm in diam / D. acutiloba
1 / Plants medium brown to yellowish, often iridescent when fresh, blades not twisted / 2
2 / Fronds rarely more than 4 cm long, less than 2 mm at widest, then narrowing abruptly toward apices; on same plant, some portions may be 2 to 3 mm wider than other places / D. ceylanica
2 / Fronds free of turf up to 5 cm long, shorter if in turf; characteristically nearly same width throughout, with truncate apices; branch dichotomies short / 3
3 / Fronds golden with bluish iridescence until removed from water, often in turf on sides of tide pools; in surface view some superficial cells having L-shaped lenticular thickenings / D. friabilis
3 / Fronds yellowish-green, iridescent, occasionally whole plant with 1-2 twirls, but fronds not twisted; no lenticular thickenings; lateral margins with many proliferations of various lengths and sizes / D. sandwicensis
Dictyota acutilobaCollector: E. Goergen, Kailua, 4/24/99

Key to species of Padina

1 / Fronds heavily calcified on ventral "inner" surface, nearly obscuring hair and sporangial lines / 2
1 / Fronds lightly calcified, mostly as a very thin sheet of gray, hair and sporangial lines clearly observable / 3
2 / Calcification very chalky and continuous on ventral "inner" surface; bright golden-yellow to orange on dorsal "outer" surface / P. melemele
2 / Calcification thick but discontinuous, tan on upper part of ventral surface, and throughout dorsal surface / P. japonica
3 / Blades distromatic throughout / 4
3 / Blades distromatic except at base, or blades polystromatic / 5
4 / Fronds split through nearly to base; base thick, with rust-colored rhizoids forming a hump / P. australis
4 / Plants not split, but blades laterally adhering to each other, frequently to the base and difficult to separate without tearing; almost always in large clumps / P. thivyae
5 / Blades distromatic in upper parts, tristromatic below; sporangia grouped above every hair line on inner surface, hairs lacking on opposite surface / P. tenuis
5 / Blades three or more layers thick / 6
6 / Blades 4 cells thick in upper frond, up to 9 cells thick below; sporangia grouped above every hair line on inner surface, hairs lacking on opposite side / P. crassa
6 / Blades mostly 3-celled (rarely 2-celled) throughout, sporangia grouped above every hair line on inner surface, but both groups alternating with a hair line on opposite surface / P. boergesenii

Padina spp.

Key to the species of Chnoospora

1 / Fronds erect from a discrete base, silky colorless hairs common along mid an upper parts of plants; growing high in the intertidal region, usually on vertical or sloping igneous rocks / C. minima
1 / Fronds decumbent to prostrate, bases spreading; axes terete, without colorless hairs; usually growing on horizontal calcareous surfaces below low tide on reef flats / C. implexa

Key to the species of Rosenvingea

1 / Fronds soft, erect but lax; branching dichotomous, axes less than 2 mm in diameter, apices hair-like / R. orientalis
1 / Fronds forming matted cushions composed of many tightly adhering branches, irregularly dichotomously divided / R. intricata

Key to species of Sphacelaria

1 / Arms of modified lateral branches (propagula) cylindrical, like a broad V / S. rigidula
1 / Arms of propagula not cylindrical, approximately triangular or club-like in outline / 2
2 / Propagula club-like, top rounded or thickened / S. novaehollandiae
2 / Propagula triangular, like a top; plant tufts dense and nearly black / S. tribuloides

Key to species of Feldmannia

1 / Plants with extensive matted rhizoidal systems endophytic among utricles of Codium species; spindle -shaped plurilocular structures near basal portion of plants / F. elachistaeformis
1 / Plants with a small number of rhizoids; endo/epiphytic on a wide variety of hosts; plurilocular structures cylindrical, distributed throughout plants below meristematic regions / F. indica

Key to species of Hincksia

1 / Intertidal, in rope-like strands, cells of filaments isodiametric to twice as long as broad, hook-like or short lateral branches present; plurilocular organs about as long as broad / H. breviarticulata
1 / Subtidal, not rope-like, cells becoming larger than twice their diameter, without hooklike lateral branches; plurilocular organs cylindrical more than twice as long as broad attached alternately or adaxially / H. mitchelliae

Hydroclathrus clathratus

Turbinaria ornata