Satellited chromosomes, systematics and phylogeny inTaraxacum (Asteraceae)

Abstract

A survey is made of the occurrence, nature and frequency of satellited chromosomes in the agamospermous genusTaraxacum. Species belonging to the 10 sections thought to be most primitive in the genus lack satellited chromosomes. In most other sections, a characteristic satellited chromosome is seen with a large euchromatic region distal to the presumed nucleolar oraniser region (NOR). In sections of a ‘precursor’ type, there is always one chromosome of this “Taraxacum type” per haploid genome. In sections thought to be of an ‘advanced’ type the number of such satellited chromosomes is very unstable, sometimes even within the same tissue. In sectionHamata, two such satellited chromosomes are invariably found in triploids. This finding strongly supports the integrity of this section, suggests that the species of the section are monophyletic, and have evolved from a single ancestor subsequent to the occurrence of obligate agamospermy. In three sections of the genus, satellited chromosomes of the “conventional type” with a very small distal euchromatic region distal to the NOR are reported for the first time in the genus.