Unrooted phylogenetic trees of Ty3/gypsy -like rt sequences (520 bp) isolated from Helianthus annuus (blue terminal branches), Helianthus petiolaris (yellow terminal branches), and hybrid derivative species Helianthus anomalus (a), Helianthus deserticola (b), and Helianthus paradoxus (c) (sequences from hybrid species are indicated by red terminal branches). Capital letters indicate the same reconstructed lineages as defined in Figure 2. The lineage defined by gray shading (lineage E') represents a candidate source lineage for proliferative retrotransposons. Phylogenetic analysis was conducted using neighbor joining . Bootstrap values (>50%) are shown for major identified lineages.