GEOGRAPHY

The center of diversity for Syngonium is in Costa Rica and Panama, which together have a total of 16 species. Costa Rica has 13 species while Panama has 11 species. Mexico is a secondary center of diversity with 8 species. Middle America (Guatemala to Costa Rica) has 8 species and the West Indies proper have but a single species (with another in Trinidad).

The most common and widespread species is S. podophyllum which ranges from Mexico to Brazil. Except for S. macrophyllum, most of the remainder are much less wide ranging and many, such as S. glaucopetiolatum, S. gentryanum, S. hastifolium, S. laterinervium, S. llanoense, S. occidentale, S. podophyllum var. peliocladum, S. sagittatum, S. sparreorum, and S. steyermarkii, are believed to be geographically isolated. Some, such as S. mauroanum, occupy special, restricted life zones while others such as S. podophyllum and S. hoffmannii occupy a wide variety of ecological habitats.

There are relatively few species of Syngonium in South America, though admittedly South America has been less well explored. In addition to the widespread S. podophyllum, which occurs in all parts of tropical South America, there is only one other species, S. macrophyllum, which ranges into South America from Central America. There are 11 species that are endemic to South America.

It is possible that Syngonium was a component of the remnant Paleogene tropical North American flora, as was suggested by Madison (1977) for the genus Monstera. Representatives of all sections of Syngonium are present in Central America, whereas only the two more common sections Syngonium and Cordatum are represented in South America. In addition, both of these sections are much better represented in Central America.

The distribution of Syngonium species does not show any of the disjunct distributional patterns for Central America that are exhibited by Monstera (Madison, 1977). Except for the three species of Syngonium already mentioned, which range from Mexico to Costa Rica or beyond (i.e., S. angustatum, S. macrophyllum and S. podophyllum), all other species in Central America are restricted either to Mexico or to Costa Rica and Panama.

Indicating that the paucity of Syngonium species in parts of Central America may be due to undercollecting is the fact that W. D. Stevens, now working on the Flora of Nicaragua, has already added S. schottianum to the flora of Nicaragua. It was previously thought to be restricted to Costa Rica and Panama.

The suggestion that Mexican species have long been isolated from those of Costa Rica and Panama is supported by the fact that only 3 Mexican species reach Panama, these being S. angustatum and the two widespread species S. podophyllum and S. macrophyllum, which range to South America.

Evidence that there may have been a long separation of populations of Mexican and Costa Rican or Panamanian species can be seen in the morphological variation among Mexican and Costa Rican populations of the two most widespread species in Central America. Both S. podophyllum and S. macrophyllum populations in Costa Rica and Panama differ in many ways from those in Mexico. These differences are discussed in the commentary following each species.