There are several lookalike Punctelia species; these can often be distinguished from P. rudecta by differences in distribution or in the nature of the reproductive structures present on the thallus.

[8] The thallus of Punctelia rudecta ranges in color from dark greenish-gray to almost blue-gray;[10] it tends to be more gray-greenish when fresh, and more brown-yellowish when dry.

The South African member of the complex, Punctelia toxodes, grows on both tree bark and rocks.

Although morphologically identical to P. rudecta, it produces lichexanthone, a secondary compound previously unknown in Punctelia.

This compound, which is present only in its pseudocyphellae, causes these structures to fluoresce when viewed under ultraviolet light and allow these otherwise identical species to be distinguished from each other.

[11] Although the range maps included in some popular North American lichen field guides suggest that it does not occur in the tropical climate of southern Florida,[10][13] it was recorded in Fakahatchee Strand Preserve State Park in 2011.

Irwin Brodo calls it "one of the most common eastern isidiate foliose lichens",[10] while Erin Tripp and James Lendemer express similar sentiments about its prevalence, describing it as "arguably the weediest macrolichen east of the Mississippi River".

[13] The lichen occurs in most Canadian provinces (Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Quebec, and Saskatchewan).

[12] In Mexico, it has been reported from the Distrito Federal, Chiapas, Veracruz, Jalisco,[16] Baja California, Chihuahua, Durango and Sonora.

[17] Punctelia rudecta has an annual radial (i.e., expanding outward from the center) growth rate of about 5 mm (0.2 in) per year, similar to other foliose lichens in the family Parmeliaceae.

[23][24] Laboratory studies established that this fungus is incapable of growing on Punctelia rudecta unless phenolic defense compounds are first removed from the lichen.

[24] Other fungal parasites that have been recorded growing on P. rudecta include Trichosphaerella buckii, Pronectria subimperspicua,[25] and an unidentified species of Cladophialophora.

[27] Based on the frequency of Punctelia rudecta in heavily polluted areas, it is considered a relatively pollution-tolerant species,[28] although it is sensitive to ambient sulfur dioxide (SO2), and will not grow unless airborne SO2 concentrations are low.

To do this, the lichen is studied for effects on growth and for the accumulation of pollutants (such as toxic heavy metals) in the thallus, which, after collecting samples, can be determined in the laboratory with chemical techniques.