Geographic variation in flower color patterns within Calceolaria uniflora Lam. in Southern Patagonia M. Masco´ 1 , I. Noy-Meir 2 , and A. N. Se´rsic 3 1 EEA Santa Cruz, Consejo Agrario Provincial, INTA & Universidad Nacional de la Patagonia Austral, Rı´o Gallegos, Argentina 2 Institute of Plant Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Israel 3 Instituto Multidisciplinario de Biologı´a Vegetal, Universidad Nacional de Co´ rdoba & CONICET, Argentina Received March 3, 2003; accepted September 7, 2003 Published online: February 3, 2004 Ó Springer-Verlag 2004 Abstract. Infraspecific variation in flower colors was evaluated in 26 populations of Calceolaria uniflora Lam. in Southern Patagonia, Argentina. Computerized analysis of high-resolution photo- images was used to estimate the proportions of red, orange and yellow in surfaces of two corolla parts, ‘‘instep’’ and ‘‘throat’’, in field samples of 20–35 flowers per population. The between-popu- lations component accounted for 48% of variance for instep colors and 24% for throat colors. Geographic differentiation was found between populations with a uniform red instep in the Andes in the west, and populations with a maculate yellow-and-red instep in the Magellanic steppe to the east. Mixed populations occurred in a transition zone. Throat colors showed a differ- ent, north-south geographic trend. Based on color pattern and distribution, two subspecies may be differentiated within C. uniflora. Their overall geographic distribution is related to climate and vegetation, but their detailed distribution is better explained by isolation by distance and barriers to gene flow. Key words: Infraspecific variation, populations, image analysis, multivariate analysis, Argentina. Introduction The patterns of variation in characters between populations within a taxon and in related taxa are the subject matter of biosystematics (Solbrig 1970, Elkington 1986, Stace 1989). Variation between geographically separated populations within a species is of special interest as an indi- cation of divergence and incipient speciation (Judd et al. 1999). Most studies of infraspecific variation at a geographic scale have been conducted in Europe and North America. There are few such studies on plants of temperate-cold regions in the southern hemisphere, such as Southern Patagonia. Biosystematic studies of angiosperm taxa often focus on morphological characters of the flower (shape, color) because they usually are phenotypically more stable than vegetative characters and vary less within populations than molecular markers (e.g. Podolsky and Holtsford 1995). Variation in flower shape and color has commonly been interpreted as ‘‘adaptive’’, resulting from disruptive selection Plant Syst. Evol. 244: 77–91 (2004) DOI 10.1007/s00606-003-0083-1