Sequences of ITS1 of Picea mariana (black spruce) and P. rubens (red spruce) are at least 2750 base pairs long, longer than the longest previously known conifer ITS1 (Pinus pinea, 2631 bp). All studied Pinaceae ITS1 contain subrepeats, regions up to 265 bp in length, containing an embedded conserved motif (GGCCACCCTAGTC), and thought to be involved in secondary structure. In Pinaceae, there is a strong association between ITS1 length and number of subrepeats. Pinus has six subrepeats, but the two Picea species reported here are exceptional in having only three subrepeats with the conserved motif. Two of these subrepeats are 189 bp in length, and the third is roughly 50 bp long. Picea ITS1 also contains two regions about 480 bp long, with high sequence similarity, and lacking the conserved motif. Variation in Picea ITS1 appears to be complex in our sample, which includes multiple clones from four individuals, representing two populations from each species. We find variation between populations and within individuals, suggesting ineffectiveness of concerted evolution as in some other conifers. Black spruce and red spruce are considered sister species, hybridize frequently, and are sometimes difficult to distinguish morphologically. ITS1 sequence divergence between these two species is 2-4%, more than that between sister species in Tsuga (three pairs of sister species), Larix (two pairs), and Pseudotsuga (one pair), but similar to that between sister species in one other pair in Pseudotsuga.

Key words: ITS, Picea, Pinaceae, sequence divergence, sister species, subrepeats