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Many have tried to estimate the number of species of organism already described, and those still awaiting description. A recent quantification of the species of asclepiad (Apocynaceae) increased the traditionally accepted totals of 2.000 - 2.500 to more than 3.000, 15 % of which were described only in the 1990s - it was argued from this that the number of asclepiads could continue to rise to 4.000 species. We tracked the change in the number of Brazilian Asclepiadoideae (with type specimens from Brazil) by evaluating the difference between new species and synonyms. Of the 585 species described from Brazil, more than 35 % are currently treated as synonyms and more than 10 % of the rremaining currently accepted names are potential synonyms. The greatest increase of species number in Brazilian Asclepiadoideae took place during the 19th century. Since the middle of 20th century, the number of accepted species started to decrease. The adoption of the type method in botanical nomenclature since 1935 is probably the main reason for such a change. The 1990s showed a slight increase in the number of accepted species, but this comes at the end of a half-century of overall decline. Trends on the numbers of species may vary according to the period examined, therefore estimates based on trends of just one 10-year period should be viewed with caution.