Ramalina sideriza is a species of strap lichen in the family Ramalinaceae, first described by German lichenologist Alexander Zahlbruckner in 1911 from Hawaiian specimens.

This shrubby lichen is characterised by its flattened thallus lobes with curled tips, a striate surface with distinct parallel ridges, and smooth apothecia (fruiting bodies).

While the Hawaiian specimens typically have marginal apothecia (reproductive structures) and a more pronounced geniculate growth (resembling bent knees), the Galápagos specimens generally display laminal apothecia (i.e., fruiting bodies throughout the thallus surface, rather than concentrated at the margins) and are only partially geniculate.

These distinctions have led researchers to suggest that further comparisons with R. sideriza samples from other locations may be necessary to confirm the identity of the Galápagos population.

[2] In terms of chemical spot tests, the medulla of R. sideriza reacts K+ yellow, slowly turning red, indicating the presence of salazinic acid.