Clinal variation in morphology from north to south and to a lesser degree from east to west is described in the widespread Neotropical species of Acisanthera sect. Acisanthera. While northernmost and southernmost species are separable from one another, they are bridged by other species which results in a complicated morphological continuum. Two important characters were detected in the data that correlate with geographic distribution: first, flowers on compound inflorescences in plants south of Amazonia and with solitary flowers north of Amazonia; and second, anther pore width from narrow (0.2 mm) in South America to wide (0.38 mm) mainly in Central America and the Caribbean. A high degree of plasticity in the first character south of Amazonia (inflorescence structure) complicates differential diagnosis between species in the southern end of their distribution. Adding leaf shape and indument helps differentiate the currently recognized species although in some cases with difficulty. These cases are discussed particularly in reference to Acisanthera variabilis. Although most continuously varying vegetative characters are positively correlated with geography, two floral characters are not (anther pore width and anther appendage connective length) which suggests differing selection pressures. Overall, partitioning of vegetative from reproductive characters indicates they are uncoupled, a result which supports Berg's correlation-pleiades hypothesis.