Key to the species of Ceramium

1	Plants with conspicuous prostrate as well as erect axes	2
1	Plants lacking or having inconspicuous prostrate axes	3
2	Tetrasporangial nodes with sporangial walls overlapping each other, giving node ballooning effect	C. hanaense R.E.Norris & Abbott
2	Tetrasporangial nodes without sporangial walls overlapping, but sporangia hiding nodal structure; vegetative nodes having simple pointed projection	C. cingulum Meneses
3	One to several conspicuous 1-3-celled spines at each node, especially protuberant near apices	C. dumosertum R.E. Norris & Abbott
3	Spines lacking at nodes	4
4	Plants mostly dichotomously branched, their apices paired and turned toward each other	C. clarionense Setch. & Gardn
4	Plants irregularly to alternately branched, their apices not turned toward each other	5
5	Nodes appreciably extending beyond width of internodes, often lower tiers of cells of nodes separated from remaining nodal cells by a horizontal line	C. flaccidum (Kützing) Ardissone
5	Nodes usually not much wider than internodes, with no separation of nodal cells	6
6	Plants alternately branched, the terminal branches sickle-shaped, partially enclosed within the next older branch; gland cells common in cortex of older nodes	C. aduncum Nakamura
6	Plants irregularly branched, branches not sickle-shaped, nodes in younger parts of plants with soft inflated cell projecting laterally	C. fimbriatum Setch. & Gardn.