Most weed families overrepresented with natives have a low proportion of exotic species in Mexico

The analysis of the distribution and abundance patterns of the families of invasive plants can be useful to reveal statistical tendencies that identify groups of plants that must be watched closely before they are allowed into a country or when they have been just introduced.  We studied abundance and distribution patterns of native and exotic weed families and examined the proportion of weeds of the world per family that are represented as native or exotic in Mexico.  The difference between the proportion of weeds of the world represented as native and introduced in Mexico varies widely among families.  The Malvaceae, Solanaceae, Lythraceae, Cucurbitaceae, Commelinaceae, Amaranthaceae, Convolvulaceae, Euphorbiaceae, Asteraceae, Capparaceae and Onagraceae have more than 20% of the weeds of the world represented as native. In those families, the proportion of natives is 3 or more times higher that the proportion exotics, but in Caryophyllaceae, Chenopodiaceae and Brassicaceae, the difference between the native and exotic proportions is very small. The families with 10% or more of the weeds of the world represented as native (except Poaceae and Caesalpinaceae) have a 40 to100% more native than exotic species. The exotic Poaceae and Brassicaceae are over-represented in Mexico, but their distribution patterns do not explain their overrepresentation. The overrepresentation of the exotic Poaceae is possibly explained by the large number of forage grasses introduced repeatedly into Mexico. The abundance of the exotic Brassicaceas in Mexico is probably due to the shortage of native weed species in comparison with the great pool of weeds of this family in the world. The pattern found with most families agrees with the hypothesis of taxonomic affinity in plant invasions and suggests that invasive weed species with low number of weed relatives within its plant family in the target region have a high probability of success.