### Patterns of morphological variation of alligator weed (Alternanthera philoxeroides): from native to invasive regions

Xiaoyun Pan1, Hanzhao Liang , Alejandro Sosa2, Yupeng Geng1, Bo Li1, Jiakuan Chen1*

1. 1 Ministry of Education Key Laboratory for Biodiversity Science & Ecological Engineering, Institute of Biodiversity Sci-ence, Fudan University, Shanghai 200433, China
2 South American Biological Control Laboratory, USDA-ARS, Hurlingham-Buenos Aires 1868, Argentina
• Received:2005-10-24 Revised:2006-03-23 Online:2006-05-20 Published:2006-05-20
• Contact: Jiakuan Chen,Xiaoyun Pan

Abstract:

The damage caused by biological invasions has traditionally been thought to result from alien species taking advantage of ecological differences between the native and introduced regions. In contrast, evidence is in-creasing that invasive plants can undergo rapid adaptive evolution during the process of range expansion. Using a common garden approach, we compared 19 morphological and anatomical traits of Alternanthera philoxeroides collected in native (Argentina) and invasive (China and USA) regions. The results show that native and invasive A. philoxeroides have become genetically differentiated. Populations from Argentina had significant morphological variation in nine traits, with heritability varying from 49% to 89%. The nine traits are stomatal density, stomatal index, diameter of stem, diameter of pith cavity, thickness of vascular cylinder, thickness of cortex, area ratio of vascular cylinder, area ratio of pith cavity, and leaf index. However, populations from introduced regions showed no significant variations in any of the 19 traits, indicating that the morphological differences within introduced regions might be based on phenotypic plasticity.Based on the result of PCA (primary component analysis), all five introduced populations and one population from Argentina (Santa Fé, 59°49′W, 29°16′S) can be clustered as one group, implying that the Santa Fé population may have similar genotypes with the lineage introduced to China. The existence of genetically differentiation of A. philoxeroides between native and introduced regions should be considered in any pro-grams that attempt management or utilization of this plant.