The somatic chromosomes of Sophora fernandeziana (Fabaceae), an endemic tree from Robinson Crusoe Island

Abstract

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 μm) and bear no satellites. The intrachromosomal and interchromosomal asymmetry indices were A1 = 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. fernandeziana, in accordance with previous studies of other endemic species in the Juan Fernández 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.