Chromosomal diversity in Philodendron (Araceae): taxonomic significance and a critical review

Abstract

The genus Philodendron is a highly diverse Neotropical group of the monocot family Araceae. Despite chromosome counts being relatively abundant for the family, information on the karyotype evolution within the genus is still scarce and very confusing. Therefore, we report diploid numbers and additional cytological features for 43 species of Philodendron, discussing the importance of our results and reviewing previous data. Species were collected in four different Brazilian biomes (Caatinga, Cerrado, Amazon basin and Atlantic Forest) and chromosome counts were based on Giemsa standard staining procedures. First chromosome counts are given for 35 species, while for another eight species counts are reported for new provenances. The majority of the species (27) presented the diploid number of 2n = 32, while the number 2n = 34, the second most frequent, was observed in eight taxa. Uncommon chromosome numbers were observed for seven species: P. callosum and P. uliginosum with 2n = 28, P. hastatum and P. melinonii with 2n = 30, P. corcovadense and P. saxicola with 2n = 36 and P. brevispathum with 2n = 40. On the other hand, two species showed variation in chromosome numbers among analysed cells: P. insigne with 2n = 30–32 and P. pulchrum with 2n = 26–28. Regarding chromosome morphologies, a prevalence of submetacentric and metacentric pairs could be observed in most species, with some taxa having a tendency to asymmetry and a higher number of acrocentric pairs. A list of all available chromosomal data is presented, considering the actual taxonomic circumscription and synonyms. Considering the present analysis and the literature data, we suggest n = 16 instead of n = 18 as the primary basic number of the genus, from which secondary base numbers n = 17, 18 and (less frequently) 15, 14 and 13 have probably been derived. Dysploidy seems to be the prevalent karyoevolutionary trend within the genus.