ASSESSING THE RELATIONSHIPS OF AUTOSPORIC AND ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE WITH 18S rDNA SEQUENCE DATA1

We examined the relationships of autosporic and zoosporic taxa in the Chlorococcales by analyzing available complete nuclear‐encoded small‐subunit (18S) rRNA gene sequences along with two new sequences fromHydrodictyon reticulatum(L.) Lagerh. andNeochloris vigenisArchibald. Some autosporic taxa grouped with the coenobial hydrodictyacean algae and related unicellular organisms having directly opposed basal bodies. These includeScenedesmus obliquus(Turp.) Kütz. andChlorella fuscavar. vacuolata Shihira et Krauss. Other autosporic organisms, includingChlorella kessleriFott et Novakova,C. minutissimaFott et Novakova,C. pro‐tothecoidesKrug.,C. vulgarisBeij.,Nanochlorum eucaryotumWilhelm, Eisenbeis, Wild, et Zahn, andPrototheca wickerhamiiSoneda et Tubaki, form a separate group. Of the zoosporic taxa examined, this group would appear to have the greatest affinity to organisms having a counterclockwise displacement of basal bodies, the Pleurastrophyceae. Beyond the fact thatAnkistrodesmus stipitatus(=A. falcatusvar.stipitatus(Chodat) Lemm.) does not group with the latter organisms, its position remains in doubt. None of the autosporic taxa appear to be closely related to chlorophycean organisms possessing a clockwise basal body displacement.