Hi Miguel, the Psidium myrtoides is the species that other people calls Psidium eugeniaefolia?
I tasted my first eugeniaefolias this week (seeds from USA or Madeira... ). They smell like guavas and the taste is similar to strawberry guavas + tropical guavas + psidium australe, but maybe more acid. Pulp is pinkish... red... white...; 2 or 4 seeds per fruit. 14º to 16º Brix (sweet), what is quite remarkable for such an acid fruit.
Does it sounds like your p. myrtoides to you? Do your p. myrtoides smells like guavas?
Also, Helton wrote about p. eugeniaefolia: " Os frutos são bagas subemisféricas (que é quase redonda) de 1,5 a 3,6 cm de diâmetro com casca roxo escura ou quase negra quando totalmente madura. A polpa é arroxeada, acidulada, envolvendo 10 a 22 sementes angulosas e de cor creme.", but mines doesnt have 20 to 22 seeds: just 2, 3 or 4..