The evolutionary split of Pinaceae from other conifers: Evidence from an intron loss and a multigene phylogeny

The second intron in the mitochondrial gene nad1 was surveyed using PCR, DN A sequencing, or Southern hybridization in 323 species (313 genera, 212 fam ilies) of seed plants. The intron was absent in all 22 species (22 genera, 8 families) of non-Pinaceae conifers studied, in Welwitschia mirabilis, and in seven angiosperms. Whereas absence of the intron in seven angiosperms a nd Welwitschia is likely due to seven independent losses when evaluated aga inst the recently published multigene phylogenies, the lack of the intron i n all non-Pinaceae conifers can be best explained by a single loss. These d ata suggest that the non-Pinaceae conifers represent a monophyletic group. We also conducted a phylogenetic analysis of seed plants using a combined d ata set of the partial exon and intron sequences of nad1 generated from thi s study and published sequences of mitochondrial cox1 and small subunit (SS U) rDNA, chloroplast rbcL, and nuclear 18S rDNA. The results supported the split of conifers into two groups: Pinaceae and non-Pinaceae conifers. The Gnetales were sister to Pinaceae, in agreement with the conclusion from oth er recent molecular phylogenetic studies that refute the anthophyte hypothe sis. (C) 2001 Academic Press.