Apomixis in the interspecific triploid hybrid fern Cornopteris christenseniana (Woodsiaceae)

Abstract

Cornopteris christenseniana is a "sterile" interspecific triploid hybrid of diploid C. crenulatoserrulata and tetraploid C. decurrenti-alata . Morphological and cytological studies show that, of 41 young plants of Cornopteris that have been propagated naturally in the Fern Garden of the Botanical Gardens, University of Tokyo, 30 plants are the sterile C. christenseniana , 10 are fertile C. decurrenti-alata and 1, fertile C. crenulatoserrulata . This proportion supports the view that the young plants of C. christenseniana are derived from spores of reproductively mature plants of the species cultivated. Cytogenetic observations and culture experiments show that C. christenseniana produces normal spores in various proportions in some sporogenetic pathways that are aberrant from the ordinary process in sexual and apomictic ferns. Under culture conditions, normal spores germinate in rough proportion to the frequency of normal spores, and sporophytes are apogamously produced in rough proportion to the frequency of spore germination. As a whole, the rates of spore germination and apogamous sporophyte development vary according to the specific plant. Taken together, these observations suggest that C. christenseniana is an incipient apomict.

Apomixis and reticulate evolution in the Asplenium monanthes fern complex

“…However, the taxonomic distribution of apomictic (asexual) taxa across plant lineages is uneven, with estimations of 0 . 1 % in angiosperms, up to 10 % in ferns, and with little or no evidence in gymnosperms, mosses, liverworts or hornworts (Walker, 1966a;Lovis, 1977;Asker and Jerling, 1992;Mogie, 1992;Pichot et al, 2001;Park and Kato, 2003).…”

Athyrium bipinnatum K.Hori (Athyriaceae), a new cornopteroid fern from Japan

“…× christensenianum. The hybrid origin of this species has been pointed out by many authors (Kurita 1964, Hirabayashi 1970, Kato 1979, Park and Kato 2003. According to these authors (Kurita 1964, Hirabayashi 1970, Kato 1979, Park and Kato 2003, this is a triploid "species" that has resulted from a cross between diploid sexual Athyrium crenulatoserrulatum Makino and tetraploid sexual Athyrium decurrentialatum (Hook.)…”

The steps from sexual reproduction to apomixis

“…However, the taxonomic distribution of apomictic taxa across the plant lineages is uneven, with estimations of 0.1% in angiosperms, up to 10% in ferns, and with little or no evidence of its existence in gymnosperms, mosses, liverworts or hornworts (Walker 1966;Lovis 1977;Asker 1992;Pichot 2001;Park 2003). Sexual reproduction is ancestral in homosporous ferns, and the transition to apomixis requires the evolution and alternation of two distinct phenomena: diplospory and apogamy.…”