Plants of Hawai'i
Division Cyanophyta (cyanobacteria or blue-green algae)
Description: filamentous seaweed black to dark
can be shades or red green or yellow. 5-10cm long may cause
swimmers itch, found with other seaweeds.
Habitat: shallow tide pools and subtidal habitats.
Division Chlorophyta (green algae)
Description: very common known as sea lettuce flat
twisted blade 1-10cm wide and 5-100 cm long. grass green in
Habitat: abundant in high nutrient water, intertidal
rocks and pools. Very common
Description: green grass color, looks like netting, up
to 3m in length.
Habitat: reef flats, and covering other seaweeds.
Description: delicate soft featherlike appearance, dark
green color make this easily recognized.
Habitat: shallow reef flats, and tidepools, and lower
intertidal habitats with low wave action. 2-12 cm long.
Description: a dark green spongy mass, 0.5-3cm thick and
up to 15cm wide. characterized by rolling bumps or convolutions
Habitat: intertidal and reef flats.
Description: forms spongy mat-like mass of many
intertwined dark green cylindrical branches. 3-8cm in diameter.
Branches attach whatever they contact.
Habitat: reef flats, in lower intertidal habitats and
in tide pools. Looks like green rat's feet.
Description: dark green with flattened branches, 1-2cm
wide attached to bottom in one place, upright.
Habitat: in fairly calm water such as deep
and on deep reef flats growing to 10cm in length.
Description: very distinct, fingerlike form grows 4cm
high, found in tide pools and reef flats, and in subtidal
Habitat: depressions of rocks. Top is green and fuzzy
and bottom is calcified and white.
Description: featherlike branches green in color 3-15cm
tall. found in sandy areas of tide pools, and reef flats. Appears
like Caulerpa sertularioides except branches are flat with
angled edges giving a square or rectangular appearance.
Description: looks like small bunches of grapes, light
green in color. and up to 4cm thick and horizontal runner which
anchors the "grapes" to the substrate.
Description: dark green outer segments; may have a
calcified and whitish center. able to anchor in sand as well as
Habitat: found in deeper waters. Dead bits of this alga
makes up a large portion of Hawaii's beach sand.
Description: calcareous green to whitish seaweed found
in deeper water between rocks in bunches. Segmented usually with
midribs. 0.5-2cm wide segments, with lengths of 30 cm.
Description: commonly known as the "Green Bubble
Alga" due to the large round cells. When small the thallus
is a hollow sphere, when larger the sphere may burst becoming
convoluted and cup shaped. The seaweed is grass green in color
and can form extensive mats over the reefs surface 1-10cm thick.
Description: like D. cavernosa, also has bubble
like cells, but is completely solid in middle and always remains
rounded. Grass green in color, but sometimes bluish in color. 1-2
cm high and 1-5 cm wide.
Description: M. japonicum is a single flattened
blade consisting of a meshwork of fine connecting branches. It is
grass-green in color, from 1 to 6cm wide and 1 to 4 cm high.
Habitat: low intertidal areas of rocky coastlines, on
flat reefs, and in between the branches of corals at deeper
Division Phaeophyta (brown algae)
Description: brown color with dark spots from 10-40 cm.
flat blades 1-2cm wide with midrib. Produces strong odor.
Habitat: abundant deep water seaweed. found in dense
beds at depths of 3-20 meter.
Description: similar to D. australis but
smaller, 5-20 cm high and narrow blades, of 0.5 -1 cm wide. Brown
with ruffled margins and a midrib.
Habitat: on rocky shores at about zero tide level and
on reef flats. and outside reef crests in deeper water.
Description: flat small twisted blades forming Y
pattern and lacks midrib. size varies from 3-20cm and light brown
Habitat: commonly found in tide pools and reef flats
and deeper subtidal habitats.
Description: exhibits a yellow green iridescence.
Blades of 2-5mm wide lack midribs, branches in a Y pattern. grows
to 12cm high.
Habitat: in tide pools and on reef flats.
Description: flat orange to dark brown seaweed 1-8cm
across, grows over rocky substrate attached in only a few places.
Description: flat seaweed, with rolled edges, light
brown in color and slightly calcified, blades may be split.
Attached by single holdfast, 5-20cm tall.
Habitat: in deep tide pools and on reef flats.
Description: flat blade rolled into a circle, upper
surface is whitish, lower surface brownish. Tends to be smaller
then P. australis, with blades not split.
Description: beautiful iridescent blue or green color.
consists of many flat blades without the in-rolled margin as in
the species Padina.
Habitat: on wave swept beaches and reef flats, brightly
colored so is noticeable.
Description: Golden to dark brown holly-leaf like
blades with mid rib and flattened stems. size is 5-70cm tall with
blades at 0.3-2cm wide.
Description: found in tide pools and reef flats. Brown
leaf like blades with midrib, round smooth main stems and gas
bladders on round smooth stalks. Size is 5-50cm tall and 0.3-2cm
Description: Many brown blades with a midrib, and when
present gas bladders with leaf like stalks. Stems show short
spiny projections and grows 5-40cm tall with blades .5-1cm wide.
Habitat: found in wave swept benches, tide
pools and on
reef flats, and occasionally deeper depths.
Description: stiff erect seaweed with distinctive
angular turban-like blades and a central stipe. Light brown color
and grows 2-20cm tall.
Habitat: on rocky intertidal coastlines in
and on reef flats and crests.
Description: hollow saclike seaweed, golden brown in
color and can have a smooth or convoluted surface. 1-5cm
diameter, up to 20cm in diameter.
Habitat: found in several habitats.
Description: dark brown-black fuzzy tuft of filaments
of all the same length. Up to 2cm tall.
Habitat: on rocky surfaces, or larger seaweeds in
tide pools on reef flats.
Division Rhodophyta (red algae)
Description: pink to red, and gooey at the ends of the
Habitat: common on reef flats and tide pools but can be
found in deeper waters.
Description: slippery round gooey branches. Branches
3-6mm in diameter and height varies from 5-40 cm. Light pink and
slightly calcified seaweed.
Habitat: grows on reef flats and in deeper subtidal
habitats to 10 m.
Description: this calcified seaweed is white to pink in
color with stiff, hollow cylindrical branches and deep pits in
Habitat: found in tide pools and reef flats where it
reaches a height of up to 15cm.
Description: looks like G. acuminata with hollow
branches. Calcified seaweed is pink to red and grows to 15cm in
Habitat: found in deep tide pools or at deeper depths.
Description: red to bluish violet color. Fluffy
appearance and shaped like a Christmas tree. grows 3-15cm high.
Habitat: in shallow subtidal habitats with heavy water
Description: this is a soft limp & slippery smooth
seaweed with somewhat flattened branches that can be red green
brown or almost black. Size and shape vary greatly from 0.5-5mm
wide and 2-30cm long. with either few or many branches.
Habitat: at zero tide, rocky coastlines and shallow
Description: many thick, lose branches forming from a
central stipe. Color varies from red to white and size from 3-12
Habitat: most commonly found growing in
of corals in waters deeper than 5 m but can be found on reef
Description: red to maroon encrusting seaweed calcified
on its lower surface. Its edges are free but the bottom remains
firmly attached to rubble, dead coral, or other hard surfaces.
Habitat: common in most subtidal habitats.
Description: produces a distinctive strong odor. Bright
red to orange-red and grows 2-6cm high with branches that are
rolled inward at the tips.
Habitat: found in almost any habitat.
Description: calcified brittle branches less then 0.5mm
and 0.3-2cm long. pink to white color.
Habitat: close examination of almost any habitat will
reveal the presence of this seaweed
Description: forms pinkish calcareous crusts or much
branched hemispherical shaped heads 10-30cm across (or larger).
Habitat: on reef crest & just seaward of crest.
Description: forms extensive pinkish to purplish chalky
crusts in intertidal areas exposed to surf action. Due to strong
tolerance to sunlight and desiccation and its crustose nature it
is extremely successful in occupying high wave energy habitats. P.
onkodes performs a critical role in the formation and
maintenance of the biotic reefs of Hawaii by providing an
actively growing reef rim, allowing consolidation and cementation
of reef material to occur in protected shoreward areas or the Porolithon
Habitat: intertidal areas exposed to surf.
Description: solid cylindrical branches 1-4mm wide with
short pointed tips. red in color but often bleaches to pink or
white in bright sunlight. Grows 6-20cm tall. When reproductive
"bumps" appear on the surface, it is illegal to collect
reproductive Gracilaria coronopifolia.
Habitat: on reef flats, but occasionally found in
Description: cylindrical branches 2-5mm in diameter,
usually distinctive constrictions. Forms mats 1-5cm thick. Bright
yellow to orange-brown.
Habitat: in tide pools and reef flats.
Description: rounded main branches 1-3mm diameter with
short pointed side branches. Length grows from 3-30cm. Bright
yellow to dark red.
Habitat: in shaded areas.
Description: branches are fluorescent red soft and
gooey. Reaches a length of 5 cm.
Habitat: in subtidal habitats between the branches of
Description: 1-3mm solid cylindrical branches. Covered
with many distinctive small spine-like branches. Grows to 3-20cm
high. Red, brown or dark green in color but turns yellow in
Habitat: abundant in calm shallow reef flats,
and intertidal benches.
Description: grows to 15cm tall is bush-like with dark
red central stipe and flattened blades 3-7mm wide. Often covered
with epiphytic crustose coralline seaweeds giving off a pink
Habitat: widespread in shaded areas of almost any
Description: Y shaped branches and usually dark red in
appearance. Size is 1mm diameter with two branches often curving
upward, creating a claw-like appearance up to 0.5-5cm long.
Habitat: grows in tufts and mats in lower tidal
habitats tide pools reef flats.
Description: round main branches 1-2mm diameter and
2-20cm long. Cylindrical branches with blunt tips with a tiny pit
in each tip. Color is highly variable, often branches are
rosy-straw colored with red tips.
Habitat: on reef flats and lower intertidal habitats
along rocky coastlines.
Description: flat seaweed. May be completely solid and
smooth or divided into a fine lacelike network on outer portion.
1-8 cm high. Variable color: pink to orange, to bluish iridescence.
Habitat: common in tide pools and reef flats.
Description: 0.5-2mm in diameter covered with any soft
fine branches creating a fuzzy appearance red to almost white in
color, but often traps fine sediment that can make it appear many
Habitat: in calm inner areas of reef flats. Soft thick
mats can cover large areas of the reef flat.
Description: filamentous red that forms loose mats from
0.3-1 cm thick. Main branches are 0.5 mm in diameter with many
smaller branches growing out from them. In deeper water it is
dark red in shallow water it appears pale red. Has distinctive
Habitat: on rubble and coral heads in subtidal
Description: dark green to blackish color. 2cm high
with flattened branches.
Habitat: common in tide pools and on reef flats.