Since this and other species of Niebla are often rather variable, there are a number of look-alikes that are tricky to separate.
N. josecuervoi from Baja California is most difficult. See Nash’s Sonoran Flora for an exhaustive discussion of these two nearly-identical species.
N. laevigata is shinier, smoother, flatter, and lacks chondroid strands in the medulla. The two often occur together and share a similarly broad range into northern California.
N. isidiascens is conspicuously isidiate with coralloid isidia.
N. combeoides often also has an angular appearance, however the branches are generally much shorter and stubbier, and never as flattened. It typically forms little “bouquets” with clumps of strictly terminal apothecia, while N. homalea has less frequent and often marginal apothecia.
N. polymorpha is supposedly more irregular, but in particular lacks the chondroid strands of N. homalea.
N. robusta is inflated and spongy.
The rest are obviously different, mostly with rounded branches, among other differences.