Sprengel's species diagnosis outlined several key features of the lichen, including its growth form (tufted, erect, branched), colouration (pale yellowish), the nature of its branchlets (shortened, capillary-like), and details about its reproductive structures (somewhat flat, yellow scutellae with paler margins).

It also specifies the habitat or substrate preference as growing on the branches of Celastrus pyracantha, to which the species epithet of the lichen alludes.

[7] Ramalina celastri typically forms a corticolous (growing on the bark of trees) thallus, which is the main body of the lichen, characterised by its rigid, erect to somewhat pendulous (hanging) structure that can reach up to 15 cm in length.

Young branches are thin and more or less smooth, transitioning as they age to develop longitudinal or reticulately (net-like) ridged surfaces.

Short linear or irregular laminal pseudocyphellae (small pores in the thallus that allow for gas exchange), are commonly present but soralia, which are structures for asexual reproduction, are absent.

[6] It is typically found in the warmer and more humid regions of Australia, specifically in New South Wales and Queensland, as well as in northern New Zealand.

In New Zealand, the rock-dwelling forms of Ramalina celastri on the North Island, found exclusively within coastal environments, showed distinct morphological differences from their tree-dwelling counterparts, characterised by a more robust structure with wider and longer thalli.