Maternal inheritance of chloroplasts in the horsetail Equisetum variegatum (Schleich.).

Reliable data concerning the transmission of chloroplasts in the Pteridophyta are needed both for phylogenies based on chloroplast DNA (cpDNA) sequences and in order to study the evolution of this trait in conjunction with the evolution of the life cycle and the sexual reproduction of land plants. For the first time, this paper describes organelle transmission in the division Sphenophyta, represented by the extant genus Equisetum. By following the fate of polymorphic cpDNA during three intraspecific reciprocal crosses we found no trace of paternal transmission in Equisetum variegatum. The seemingly strict maternal transmission of cpDNA in this species suggests that uniparental chloroplast inheritance preceded the evolution of heterospory in the seed-plant lineage.