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Niebla homalea
is primarily a California species recognized by the presence of
the lichen substance divaricatic acid, and by the development of partly to
almost entirely linear branches with a hard,
thick glossy cortex bearing transverse cracks at frequent intervals. The
branches frequently twist between the base and apex, in contrast to twisting in
N. eburnea more near the base and apex. A further distinction is the
presence of an "epicortex" in N. homalea, in contrast to
lack of development in N. eburnea, a feature that appears like a coat of gloss above
a keratinous melanized layer, which overlies a clear prosoplectenchymatous
(“mechanical”) layer, described by Bowler (1981). Spjut (1996), however,
emphasized the linear shape of branches in distinguishing N. homalea from
N. eburnea with regard to occasional intermediates that may be recognized
by having dilated branch segments, which might be treated as a distinct
variety or species to help further separate these entities. Other
Californian species such as N. disrupta seem to differ only by a single
feature such as sekikaic acid, or N. testudinaria that is
recognized by the reticulate cortical ridging in which the branches appear more prismatic.
The intermediate
specimens between N. eburnea and N. homalea, which have
twisted branches between apex and base and/or a glossy cortex, require consideration to other character features
for identification such as development of dilated branch segments and thickened vs.
wing-like branch margins. Specimens with apical flattened, often
expanded, segments are clearly associated with N. eburnea, while
both species can have dilated segments in the mid region and entirely
narrow branches. Branches of N. homalea are often more
sharply compressed near margins so as to appear narrowly winged, whereas
those of N. eburnea are often notably thickened along margins
and/or near apex due to what appears to be an aborted development of
apothecia (or nodular branchlets). The thickened
branch margins along with the ivory-like glazed cortex is usually
characteristic for N. eburnea, in contrast to the entire thinner
branch margins of N. homalea.
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