Heliconia rostrata Ruiz & Pavon inflorescences with circular necrotic spots symptoms were collected in Atalaia and Rio Largo, Brazil, in December 2016. Colletotrichum-like isolates were obtained by single-spore culture in potato dextrose agar (PDA) according to Sutton (1992). The isolates produced white cottony aerial mycelium, the underside of the colony was uniformly white with a growth rate of 10.4 mm/day. Conidia were 9.66–17.40 × 5.01–8.00 μm (n = 50), straight to cylindrical, hyaline and aseptate; morphological characters were consistent with Colletotrichum gloeosporioides. To confirm the identity of the isolate, partial sequences of the internal transcribed spacer of rDNA region, glyceraldehyde-3-phosphate dehydrogenase, calmodulin, chitin synthase and actin genes were amplified (Weir et al. 2012) and sequenced (GenBank accession Nos. MH151141, MH151150, MH151136, MH151146 and MH151131, respectively). A Bayesian inference phylogenetic tree (Supplementary Fig. S1) was constructed using a combined sequence alignment and Colletotrichum gloeosporioides species complex reference sequences, and C. boninense was used as outgroup. Isolate COUFAL0198 was identificated as C. siamense. To confirm pathogenicity, 20 μl conidial suspension droplets (106 conidia/ml) were deposited on the inflorescences wounded with a sterile needle. Control received sterile water. Typical anthracnose symptoms were observed in inoculated inflorescences in all inoculated inflorescence after 5 days (Supplementary Fig. S2). No symptoms were observed on the control. The C. siamense was re-isolated from diseased inflorescences, fulfilling Koch’s postulates. To our knowledge, this is the first report of C. siamense causing anthracnose on Heliconia rostrata in the world.