Key to common red algae of southern O'ahu

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 algal specialist if you have questions.

This key is intended for students working to identify very common red algae from the south shore of O’ahu. With the 20 taxa presented here, you will see a small sampling of the over 400 species in about 135 genera of red algae in our Hawaiian algal flora. Isabella Abbott October 1998

	Hold plant up to the light; can you see light through the main axes (the largest branches)?
	If yes	go to 1
	If no	go to 2
1	Plants slippery, light pink or yellowish with short, irregular branches on all sides, apices dome-shaped	Champia parvula
1	Plant not slippery, dark red to rusty with branches formed dichotomously; apices like pincers	Centroceras clavulatum
2	Thalli consisting of blades with smooth, uninterrupted portions alternating with coarse netlike areas	Martensia fragilis
2	Thalli not bladelike	3
3	Erect, branching in one plane; if plant is placed in water or in the palm of your hand, it will lie flat like a feather	4
3	Erect, much-branched, like small bushes, branching in various directions	7
4	Plants bright red, branching opposite, tips of branches curling over on themselves	Portieria hornemannii
4	Plants dark red to purple at base, becoming lighter colored toward top; upper parts of plants lying flat, lower parts may be irregular	5
5	Plants growing in extensive clumps along edges of benches and places where surf is rough; bottoms of plants tenacious	Pterocladiella capillacea
5	Plants inhabitants of rocky areas as well as surrounded by sand, from a variety of tidal levels	6
6	Axes of plant and axes of laterals usually nearly the same size; apices of each usually blunt; plants dark greenish brown to nearly black	Pterocladiella caerulescens
6	Flattened axes having slender branched or unbranched laterals from bases to apices, plants dark red, often purplish; plants pyramidal in shape	Grateloupia filicina
7	Thalli limey, hard or chalky, branching irregular or regularly dichotomous	8
7	Thalli not limey or hard, often crisp or cartilaginous	11
8	Plants frequently chalky white with rose-pink tips, sometimes lime accompanied by slippery substances making surface soft	Liagora species
8	Plants never chalky white , not slippery, surfaces rather stiff	9
9	Plant surfaces associated with conspicuous colored hairs, sometimes covering limey portions; in other species, only near lower parts of plant; branching subdichotomous	Galaxaura species
9	Plant surfaces without hairs; branching irregularly or dichotomous	10
10	Plants up to 5 cm tall, several axes arising from a crustose base, branching irregular to pinnate; occurring on outer reef flats	Haliptilon subulatum
10	Plants 2 cm tall, dichotomously branched with no joints unbranched between each dichotomy; frequent epiphyte on low intertidal algae	Jania adhaerens
11	Thalli with "fluffy" branches (branches in soft clumps)	12
11	Thalli with branches not in soft clumps, variously textured including "crunchy", "rubbery" and "like petals"	13
12	Plants having creeping portion bearing erect axes that are naked for 1/3 to ½ the length, but with a plume-like top bearing the soft branches	Asparagopsis taxiformis
12	Fluffy, furry branches dispersed along entire axes and irregular branches; plants rusty-pink occurring in clumps; branching pattern usually confused by presence of many epiphytes	Spyridia filamentosa
13	Plants more or less dichotomously branched, texture smooth and crunchy	14
13	Plants dominated by clear central axes, textures variable	15
14	Plants with branching opening outward, tending to sprawl; branches about the same diameter as axes; rose colored; common in all nearshore habitats to more than 4 m depths	Gracilaria coronopifolia
14	Plants with branches tending to be tightly covering each other (imbricate), tending to form spreading clumps; light to dark brown, purplish in lower shaded parts; occurring in nearshore habitats , including sandy-muddy bottoms	Gracilaria salicornia
15	Central axes erect, plants with short spinous branches along axes from base to top; sparingly or repeatedly branched; dark brown to black; frequently intertidal dominant	Acanthophora spicifera
15	Central axes persisting through length of plant, branches variously arranged along axes	16
16	Plants sprawling, branching irregular in placement and in branch lengths, long and short branches mixed along axes and major branches; frequent epiphytes on large algae	17
16	Plants erect or in clumps but not sprawling	18
17	Plants usually yellowish, spreading as much as 25-30 cm; short branches usually colored orange or rusty, contrasting with color of axes	Hypnea cervicornis
17	Plants rose colored, long branches frequent, dominating short branchlets; most branchlets with conspicuous hooked ends, attached to other algae as well as itself	Hypnea musciformis
18	Plants erect, growing singly or in small groups; sturdy naked axes in lower parts, branching toward the tops where 1-2 rosettes of leaf-like branches terminate axes	Melanamansia glomerata
18	Most species erect, like small trees that are branched all around; branches also dividing in the same way, but the youngest branches in most species often appearing short and knobby; in some species that are flattened or compressed, only short knobs occur along margins	Laurencia species