Pathways of karyological differentiation in palms (Arecaceae)

Karyological data are given for 56 palm taxa coming from all 6 palm subfamilies. In 11 genera and 17 species, chromosome numbers are reported for the first time. Most chromosome numbers in palms range between 2n = 36 and 2n = 26 in dysploid series. Species of the same genus usually exhibit identical chromosome numbers which additionally may be constant in larger groups of closely related genera (Coryphoideae trib.Corypheae with nearly always 2n = 36,Arecoideae subtribesEuterpeinae andRoystoneinae with 2n = 36,Arecoideae subtrib.Butiinae with mostly 2n = 32). Polyploidy among palms is of minor significance but the endemic Madagascan genusVoanioala (2n = 606 ± 3) is the most striking exception. — With respect to structure of interphase nuclei and longitudinal differentiation of prophase and metaphase chromosomes, the palm family is highly differentiated. Euchromatin types with different prophase condensation properties and fluorochrome and C-banding patterns of heterochromatin permit a discrimination of several subfamilies on the nuclear level (Arecoideae, Ceroxyloideae, Nypoideae, Phytelephantoideae, Calamoideae).Arecoideae andCeroxyloideae, andNypoideae andPhytelephantoideae have some features in common. Subfam.Coryphoideae s. l. is a non-uniform group. — Nuclear characters among palms exclusively found in recentCoryphoideae subtrib.Thrinacinae link palms with other monocotyledons. Most probably, such a nuclear condition represents an ancestral state in the evolution of palm genomes within subfam.Coryphoideae s. l., but also the conspicuous nuclear characters of the other modern palm subfamilies appear to be derived from a similar starting point, since transitional character states are still present in subfam.Calamoideae and some taxa of subfam.Arecoideae. Early karyoevolution in palms obviously did not involve numerical change of the ancient chromosome number of 2n = 36 which started subsequently, as a dysploid reduction in numerous parallel series, independent in subfam.Coryphoideae (2n = 36 to 2n = 28),Calamoideae (2n = 36 to 2n = 26),Ceroxyloideae (2n = 34 to 2n = 26), andArecoideae (2n = 36 to 2n = 28). Possible mechanisms of karyological change are discussed. — Karyological characters are compared to morphological, ecological, taxonomical, and chorological features, and give some new insight into older and more recent phases of palm evolution. (1) Strong deviations in vegetative or floral morphology are often accompanied by major karyological differences, and sometimes the direction of advancement can be traced through intermediate stages. (2) Apart fromCoryphoideae subtrib.Thrinacinae, the strongest concentration of apparently original karyological traits is found in the more basal members of each subfamily. (3) The most successful and actively radiating colonizers of the forest floors in evergreen tropical forests which belong to completely different subfamilies (Old WorldLicuala, New WorldChamaedorea andGeonoma), appear to be very advanced karyologically.