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

Reliable data concerning the transmission of chloroplasts in the Pteridophy ta are needed both for phylogenies based on chloroplast DNA (cpDNA) sequenc es and in order to study the evolution of this trait in conjunction with th e evolution of the life cycle and the sexual reproduction of land plants. F or the first time, this paper describes organelle transmission in the divis ion Sphenophyta, represented by the extant genus Equisetum. By following th e fate of polymorphic cpDNA during three intraspecific reciprocal crosses w e found no trace of paternal transmission in Equisetum variegatum. The seem ingly strict maternal transmission of cpDNA in this species suggests that u niparental chloroplast inheritance preceded the evolution of heterospory in the seed-plant lineage.