The Stylonematophyceae is an early diverging red algalclass that contains organisms in which sexual reproductionhas not been reported. Previous studies havehypothesized a single copy of the actin gene in thisclass. Amplification of the actin gene in members of theStylonematophyceae, including several isolates of Stylonemaalsidii, reveals a more complex evolutionaryhistory. The data support independent gene duplicationsin Goniotrichopsis reniformis and Stylonemaalsidii. Three of the seven isolates of S. alsidii had threecopies of actin. Analyses indicate that all copies arefunctional and not pseudogenes. Due to our lack ofknowledge of the ploidy level in Stylonema and theasexual nature of these organisms, an ancient changein ploidy level, producing diploid or even triploid organisms,cannot be ruled out to explain two copies of actinwithin these organisms. Within Stylonema alsidii two ofthe actin copies (Groups 1 and 2) show similar levels ofvariation; p-distances and the number of synonymousand non-synonymous sites are roughly the same. Yet thechanges are distributed differently. One group showedlittle shared variation among the samples, mutationstherefore represent autoapomorphies, while variation inthe other group is usually shared among samples(parsimony-informative). Variation in the other group isusually shared among samples (parsimony-informative).A third group of actin genes also observed in S. alsidiiare highly divergent from the other two copies, yet theymaintain all of the signatures of functional proteins.Our data reveal a complex evolutionary history of theactin gene in these species and highlight the lack ofknowledge into the basic biology (ploidy level, life cyclecharacteristics) of this class.