Diagnostic characters of the lichen include the continuously sorediate, green-and-brown-mottled, podetia that taper upward to a point, while chemically, it contains homosekikaic and sekikaic acids.

Its reduced capacity to bioaccumulate toxic heavy metals from its surroundings, as well as its ability to switch photobiont partners, allows the lichen to colonize and survive highly polluted habitats.

[11] Leo Spier and André Aptroot conducted a chemical and morphological study on about 350 mostly West European specimens of Cladonia subulata and C. rei.

They concluded that there was "no indication of any correlation between chemistry and geography, morphology or substratum", and that C. rei should be considered a chemotype of Cladonia subulata, rather than a distinct species.

Authors of a study of this taxon in Poland argued that the species should remain distinct, largely because "Their conclusions were based on material mostly from the Netherlands, with rather scanty representatives from other countries".

[5] It is prudent to take heed of Spier and Aptroot's thoughts: "There is much individual variation between the specimens, which can vary from nearly unbranched to cup-shaped, from slender (less than 1 mm thick) to robust (reaching 5 mm) and from low (average height below 2 cm) to high (height over 5 cm, clearly higher than the surrounding Cladonia species).

In Krompachy (Slovakia), the lichen, along with the moss Ceratodon purpureus, was found to be very abundant in bare acid soil near copper smelters, where all vascular plants were severely damaged or have disappeared.

Historical records and collections suggested that the lichen was broadly distributed but rare in the province, but more recent material from surveys conducted by the Alberta Biodiversity Monitoring Institute showed that its distribution is entirely limited to the dry mixed grassland, northern fescue grassland and aspen parkland natural regions, where it is relatively common.

It is widely distributed in Europe, having been recorded in Austria, Belgium and Luxemburg, Czech Republic, Estonia, Lithuania, Norway, Poland, Slovakia, Spain, and Sweden.

[30] In the United States, it has been considered by some authors to be widely distributed in the northwestern part of the country, but probably because of misidentification with the much more common C. ochlorochlora and C. verruculosa.

Samuel Hammer suggests that the actual range in the region is limited to interior localities east of the Cascade Mountains, in Idaho and Washington.

The lichen has developed a restrained heavy-metal accumulation pattern that limits its exposure to these toxic compounds, and helps it to colonise these contaminated sites.

[32] Its high genetic variability within a single population is suggestive of great potential for colonising anthropogenic habitats, and underlies the role of this lichen as a pioneer in the early stages of natural regeneration of these contaminated sites.

Its erect and fruticose growth form help it survive in this polluted environment, due to the decrease in metal content along the vertical gradient of the thallus.

The amount of cell damage can be measured experimentally by determining relative electrical conductivity, and thus, this physiological parameter can serve as an early warning indicator for detection of elevated metal concentrations in soil.

In non-polluted sites, typical lichen associations include C. chlorophaea, C. fimbriata, C. pyxidata, Ceratodon purpureus, and Peltigera didactyla.

[37] Some cryptogamic communities, including those involving C. rei, are quite similar in Europe and North America, even though the vascular plant species composition often differs considerably.

Because of the great variation in the growth forms of its podetia, densely covered with propagules such as corticated granules, squamules and microsquamules as well as numerous non-corticated, farinose-to-granular soredia, the surface area/volume ratio of the lichen is higher compared to other studied Cladonia species.

Although Cladonia lichens were previously thought to be restricted to Asterochloris, they are able to start the relichenization process with Trebouxia under specific habitat conditions and to establish a stable association with these algae when colonization of disturbed sites takes place.