The SELF PRUNING (SP) gene controls the regularity of the vegetative-reproductive switch along the compound shoot of tomato and thus conditions the 'determinate' (sp/sp) and 'indeterminate' (SP_) growth habits of the plant. SP is a developmental regulator which is homologous to CENTRORADIALIS (CEN) from Antirrhinum and TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS T (FT) from Arabidopsis. Here we report that SP is a member of a gene family in tomato composed of at least six genes, none of which is represented in the tomato EST collection. Sequence analysis of the SP gene family revealed that its members share homology along their entire coding regions both among themselves and with the six members of the Arabidopsis family. Furthermore, members of the gene family in the two species display a common genomic organization (intron-exon pattern). In tomato, phylogenetically close homologues diverged considerably with respect to their organ expression patterns while SP2I and its closest homologue from Arabidopsis (MFT) exhibited constitutive expression. This research focusing on a plant of sympodial growth habit sets the stage for a functional analysis of this weakly expressed gene family which plays a key role in determining plant architecture.