Molecular-cytotaxonomy of Cycas (Cycadales) Using 5S Ribosomal DNA Markers(Part Two Natural History Study)

Kokubugata Goro, Forster Paul I.

Somatic chromosomes of fourteen species of Cycas (Cycadaceae, Cycadales; Stevenson, 1992) were compared by the fluorescence in situ hybridization (FISH) method using 5S ribosomal DNA (5S rDNA) probes. The fourteen species of Cycas showed the same chromosome number of 2n=22, and a similar karyotype consisting of 4st, 12t, 4sm and 2m chromosomes. In the FISH comparison, C. revoluta, C. taitungensis, C. wadei, C. diannanensis and C. micholitzii exhibited a 5S rDNA site on two t chromosomes in a metaphase complement. On the other hand, C. siamensis, C. circinalis, C. cairnsiana, C. couttsiana, C. media, C. megacarpa, C. micronesica and C. thouarsii exhibited a 5S rDNA site on four t chromosomes in a metaphase complement. The two cytological groups based on the number of 5S rDNA agreed with the taxonomic treatment and phylogenetic hypothesis suggested by Hill (1996, 2004), but disagreed with those by De Laubenfels and Adema (1998). Recognition of the genus Epicycas as discrete from Cycas is not justified on the basis of cytology.

Molecular-cytotaxonomy of Cycas (Cycadales) Using 5S Ribosomal DNA Markers(Part Two Natural History Study)

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