Monophyly of Genera and Species of Characeae based on rbcL Sequences, with Special Reference to Australian and European Lychnothamnus barbatus (Characeae: Charophyceae)

Abstract

Sequences for the chloroplast-encoded large subunit of the Rubisco gene (rbcL) were used to test the monophyly of multiple isolates within species, and multiple species within genera, of green algae in the Characeae (Class Charophyceae). Parsimony and maximum likelihood analyses supported the monophyly of genera and most species, with the exception of a paraphyletic assemblage comprising isolates of two ‘species’, dioecious Chara connivens Salzm. ex A.Br. and monoecious C. globularis Thuill., which together constitute a monophyletic group. The rbcL data support the independent evolution of either monoecious or dioecious sexual systems in the two connivens-globularis, clades. Comparisons of disjunct isolates of the monotypic Lychnothamnus barbatus (Meyen) Leohn. revealed nearly identical rbcL sequences in isolates from Croatia, Germany and Australia, although all three sequences were unique. The variation exhibited by these isolates was similar to variation between isolates within species of Chara and Lamprothamnium from different continents. The limited variation may be due to dispersal of thalli or oospores between continents; however, the rarity of known intercontinental transfers of Characeae in the last two centuries suggests that the Australian population is probably not an exotic from Europe. Lychnothamnus barbatus populations in Australia and elsewhere thus merit continued protected status.