Chromosome numbers in Homalolepis Turcz. and their significance in Simaroubaceae evolution

Homalolepis was described by Turczaninow in 1848 and reestablished by Devecchi et al. in 2018, enclosing mostly the extra-Amazonian species previously included in two sections of Simaba Aubl.. We performed the first cytogenetic analysis in Homalolepis and, by surveying chromosome numbers of other Simaroubaceae representatives, reconstructed the evolution of chromosome numbers in the family, using ChromEvol software. The four Homalolepis species showed 2 n = 32 and two or four CMA + bands. In situ hybridization showed a diverse distribution of ribosomal DNA sites (5S and 18S), positioned on the same chromosome pair in H. floribunda (A. St.-Hil.) Devecchi & Pirani or on different chromosome pairs in H. arenaria (Devecchi & Pirani) Devecchi & Pirani. The basic chromosome number here indicated for Simaroubaceae is x = 12, from which chromosome numbers of other genera were derived by ascending dysploidy, with polyploidy occurring in Ailanthus Desf. only. Homalolepis presents x = 16, derived by ascending disploidy.