PATHWAYS OF KARYOLOGICAL DIFFERENTIATION IN PALMS (ARECACEAE)

Karyological data are given for 56 palm taxa coming from all 6 palm su bfamilies. In 11 genera and 17 species, chromosome numbers are reporte d for the first time. Most chromosome numbers in palms range between 2 n = 36 and 2n = 26 in dysploid series. Species of the same genus usual ly exhibit identical chromosome numbers which additionally may be cons tant in larger groups of closely related genera (Coryphoideae trib. Co rypheae with nearly always 2n = 36, Arecoideae subtribes Euterpeinae a nd Roystoneinae with 2n = 36, Arecoideae subtrib. Butiinae with mostly 2n = 32). Polyploidy among palms is of minor significance but the end emic Madagascan genus Voanioala (2n = 606 +/- 3) is the most striking exception. - With respect to structure of interphase nuclei and longit udinal differentiation of prophase and metaphase chromosomes, the palm family is highly differentiated. Euchromatin types with different pro phase condensation properties and fluorochrome and C-banding patterns of heterochromatin permit a discrimination of several subfamilies on t he nuclear level (Arecoideae, Ceroxyloideae, Nypoideae, Phytelephantoi deae, Calamoideae). Arecoideae and Ceroxyloideae, and Nypoideae and Ph ytelephantoideae have some features in common. Subfam. Coryphoideae s. 1. is a non-uniform group. - Nuclear characters among palms exclusive ly found in recent Coryphoideae subtrib. Thrinacinae link palms with o ther monocotyledons. Most probably, such a nuclear condition represent s an ancestral state in the evolution of palm genomes within subfam. C oryphoideae s. l., but also the conspicuous nuclear characters of the other modem palm subfamilies appear to be derived from a similar start ing point, since transitional character states are still present in su bfam. Calamoideae and some taxa of subfam. Arecoideae. Early karyoevol ution in palms obviously did not involve numerical change of the ancie nt chromosome number of 2n = 36 which started subsequently, as a dyspl oid reduction in numerous parallel series, independent in subfam. Cory phoideae (2n = 36 to 2n = 28), Calamoideae (2n = 36 to 2n = 26), Cerox yloideae (2n = 34 to 2n = 26), and Arecoideae (2n = 36 to 2n = 28). Po ssible mechanisms of karyological change are discussed. - Karyological characters are compared to morphological, ecological, taxonomical, an d 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 diffe rences, and sometimes the direction of advancement can be traced throu gh intermediate stages, (2) Apart from Coryphoideae subtrib. Thrinacin ae, the strongest concentration of apparently original karyological tr aits is found in the more basal members of each subfamily. (3) The mos t successful and actively radiating colonizers of the forest floors in evergreen tropical forests which belong to completely different subfa milies (Old World Licuala, New World Chamaedorea and Geonoma), appear to be very advanced karyologically.