The fatty acid composition of the tropical genus Halimeda (Halimediaceae, B
ryopsidales), represented by the six Caribbean species Halimeda opuntia (Li
nnaeus) Lamouroux, Halimeda goreauii (W. R. Taylor), Halimeda copiosa Gorea
u et Graham, Halimeda monile (Ellis et Solander) Lamouroux, Halimeda simula
ns Howe, and Halimeda incrassata (Ellis) Lamouroux, is reported for the fir
st time. The six species possessed similar fatty acid compositions with som
e exceptions. Principal fatty acids were 14:0, 16.0, 18:2 (n-6), and 18:3 (
n-3), followed by 20:4 (n-6), and 20:5 (n-3). These species contained only
16:3 and no 16:4 as the key C-16 polyunsaturated fatty acid. In the species
of Halimeda studied the 18:1 (n-7) /18:1 (n-9) ratio was less than I, with
the exception of H. monile where it was close to I. The very long-chain fa
tty acids tetracosanoic acid (24:0), pentacosanoic acid (25:0), and hexacos
anoic acid (26:0), were identified in H. copiosa, H. monile, and H. incrass
ata. The Delta 5,9 fatty acids 18:2 (n-9) and 20:2 (n-11) (H. monile) plus
26:2 (n-17) (H. copiosa) were identified in algae for the first time.