Coding and noncoding plastid DNA in palm systematics

Plastid DNA sequences evolve slowly in palms but show that the family is mo nophyletic and highly divergent relative to other major monocot clades. It is therefore difficult to place the root within the palms because faster ev olving, length-variable sequences cannot be aligned with outgroup monocots, and length-conserved regions have been thought to give too few characters to resolve basal nodes. To solve this problem, we combined 94 ingroup and 2 4 outgroup sequences from the length-conserved rbcL gene with ingroup and a lignable outgroup sequences from noncoding rps16 intron and trnL-trnF regio ns. The separate rps16 intron and trnL-trnF region contained about the same number of variable sites (autapomorphies not included) as rbcL, but gave h igher retention indices and more clades with bootstrap support. In general, the strict consensus tree based on combined rbcL, rps16 intron, and trnL-t rnF data showed more resolution towards the base of the palm family than pr evious hypotheses of relationships of the Arecaceae. An important result wa s the position of subfamily Calamoideae as sister to the rest of the palms, but this received < 50% bootstrap support. Another result of systematic si gnificance was the indication hat subfamily Phytelephantoideae is related t o two tribes from subfamily Ceroxyloideae, Cyclospatheae and Ceroxyleae.