STYLE MORPH FREQUENCIES IN MINNESOTA POPULATIONS OF LYTHRUM (LYTHRACEAE) .2. TRISTYLOUS L SALICARIA L

Style morph frequencies (short:mid:long) were determined for a total o f n=11 918 plants in 16 Minnesota populations of Lythrum salicaria L. Nine populations were in the establishment phase, with population size s ranging from n=56 to n=2 192. Most of these populations exceeded pre viously reported population sizes in the native European habitat. A no nparametric statistical test, the chi-square (chi(2)), can be used to determine if populations are at isoplethic equilibrium (1:1:1, short:m id:long); a chi(2) value > 5.99 is significant at the 5% level. Only o ne established population (White Bear Lake, n=1 991, chi(2)=3.0) fitte d the null hypothesis for isoplethy, although all established populati ons contained all three style morphs. Pooled values for these populati ons indicated an excess of mids and longs, with shorts being deficient . Colonizing populations had a higher percentage of mids (54%) when co mpared to established populations (33.7%). Short styles were almost no nexistent (8%) in colonizing populations. Five out of the seven popula tions lacked at least one style morph. A review of the literature repo rting style morph frequencies in tristylous L. salicaria revealed that no statistical analysis for isoplethy has been performed. Darwin orig inally assumed that all populations would be isoplethic, possessing eq ual numbers of all three style morphs, but concluded, without statisti cal analysis, that, instead, populations were anisoplethic. Since test s for statistical deviations from the expected frequencies (1:1:1) hav e not been used, chi(2) analysis was performed. Several of these popul ations were at isoplethic equilibrium (Nadder chi(2)=1.7, Blelham chi( 2)=1.69, Potsdam chi(2)=1.5, Vestfold chi(2)=0.4, Buskerud chi(2)=5.62 , Kilchberg chi(2)=0.35, Lausanne chi(2)=3.32, Canberra chi(2)=5.29, M assachusetts chi(2)=3.13), suggesting that the general conclusion of a nisoplethy in tristylous L. salicaria is inappropriate.