The Somatic Chromosomes of Sophora jernandeziana ( Fabaceae ) , an Endemic Tree from Robinson Crusoe Island 1

The mitotic chromosome number and karyotype of Sophora fernandeziana (Phil.) Skottsb. (subfamily Papilionoideae) are reported for the first time. The chromosome number, 2n = 18, is the modal number reported for the genus. The chromosomes are small (average length 1.55 ± 0.23 J.1m) and bear no satellites. The intrachromosomal and interchromosomal asymmetry indices were AI = 0.26 and A2 = 0.18, respectively. This symmetrical karyotype is composed of 7 metacentric + 2 submetacentric pairs. This species is related to S. tetraptera J. Mill. from New Zealand. Both share the same chromosome number; unfortunately comparative karyotype data are not available for S. tetraptera. Our data suggest that no changes in chromosome number have occurred during the speciation of S. jernandeziana, in accordance with previous studies of other endemic species in the Juan Fernandez flora and for island endemics in general. However, only a small percentage of actual karyotypes of island endemics have been studied, so generalizations about chromosomal evolution for such species are not yet well founded. ROBINSON CRUSOE ISLAND (Masatierra) is one of the three islands of the small Juan Fernandez Archipelago in Chile. It is located in the Pacific Ocean, 667 km W of continental Chile at 33° S latitude, having an estimated age of ca. 4 million yr old (Stuessy et al. 1984). The archipelago is well known for the high level of endemism among vascular plants (ca. 63% of the flora [Marticorena et al. 1998]). Unfortunately, currently more than 62% of the flora is considered rare, and two species are already extinct (Stuessy et al. 1998). The flora is threatened by both 1 Support was provided from the National Science Foundation (U.S.A.), Consejo Nacional de Investigaciones Cientfficas y Tenicas (CONICET), and Consejo de Investigaciones Cientfficas y Tecnologicas de la provincia de Cordoba (CONICOR) (Argentina). Manuscript accepted 31 March 2000. 2 Instituto Multidisciplinario de Biologia Vegetal, C. C. 495, 5000 Cordoba, Argentina. 3 The University of Connecticut, Department of Ecology and Evolutionary Biology, Storrs, Connecticut