New chromosome counts in Streptocarpus (Gesneriaceae) from Madagascar and the Comoro Islands and their taxonomic significance

This study records the chromosome numbers of 10 species of Streptocarpus; nine of the counts are new. With the exception of S. buchananii of mainland Africa, all the results are for plants endemic to Madagascar and the Comoro Islands. While there is a strong correlation between basic number and growth form in the two subgenera of the genus on the African mainland (x = 15 among caulescent species in subgenus Streptocarpella; x = 16 among acaulescent species in subgenus Streptocarpus), the situation appears more complex among Madagascan and Comoro Island species. One notable example of deviation from this correlation is shown by S. papangae, a shrubby caulescent species, with 2n = 32 (x = 16). Polyploidy in the genus appears to be absent on mainland Africa, but is present in Madagascar and the Comoro Islands, ranging from tetraploidy to octoploidy. Evolutionary implications of the cytological observations are considered.