Reproductive strategies in lichens are a rarely studied field, and little is known about which variables affecting the production of reproductive structures are most important. Here, we investigated how lichen size and cardinal direction affected the density of apothecia in the cyanolichen Leptogium marginellum. We hypothesized that larger thalli and thalli facing south (towards the pole) would have a higher density of apothecia. Individuals with larger body sizes may store more resources that can be invested in sexual reproduction, and thalli facing south in the southern hemisphere could be exposed to more favorable abiotic conditions, similar to the north in the northern hemisphere. We collected L. marginellum thalli along a stream in a protected southeast Brazil area. Cardinal directions and the largest diameter of each thallus were registered with a GPS and a digital pachymeter, respectively. We observed the thalli with a stereomicroscope, delimited a region of 1×1 cm, and photographed it to count the number of apothecia with ImageJ. We found that cardinal direction did not affect the body size or the density of apothecia. However, lichen size was an important variable in the density of apothecia, explaining almost 60% of the variation observed. According to our findings, reproduction can be considered an allometric process, and reproductive patterns can vary with the hemisphere where the lichen is found. To our knowledge, this is the first research studying reproductive allocation in a tropical lichen. Keywords: Allometry; apothecia; body size; cardinal directions; lichen ecology; life-history strategy; reproductive allocation.