Polyploidy in gymnosperms-a reappraisal

Abstract

Recent polyploidy in gymnosperms is unusually scarce being present in only 9.80 % of the 714 taxa studied cytologically. Polyploid forms are represented by sporadic seedlings and individual trees, intraspecific polyploidy in cultivation or in wild and entirely polyploid species and genera. Polyploidy shows a non-random distribution in different genera being mostly prevalent in Ephedra and Juniperus, besides the classic examples of Sequoia and Fitzroya. Remarkably, both Ephedra and Juniperus show adaptive radiation by interspecific hybridization followed by polyploidy while in Ginkgo viable polyploid cytotypes are found in cultivation. Induced polyploidy has not provided any tangible results in the past but recent attempts on certain genera of Cupressaceae hold some promise of producing cultivars for horticulture trade. Lastly, various evidences derived from cytological analysis, fossil pollen, guard cells and comparative genomic studies indicating the occurrence of paleopolyploidy have been discussed.