Coding and noncoding plastid DNA in palm systematics

Plastid DNA sequences evolve slowly in palms but show that the family is monophyletic and highly divergent relative to other major monocot clades. It is therefore difficult to place the root within the palms because faster evolving, 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 24 outgroup sequences from the length-conserved rbcL gene with ingroup and alignable outgroup sequences from noncoding rps16 intron and trnL-trnF regions. The separate rps16 intron and trnL-trnF region contained about the same number of variable sites (autapomorphies not included) as rbcL, but gave higher retention indices and more clades with bootstrap support. In general, the strict consensus tree based on combined rbcL, rps16 intron, and trnL-trnF data showed more resolution towards the base of the palm family than previous hypotheses of relationships of the Arecaceae. An important result was the position of subfamily Calamoideae as sister to the rest of the palms, but this received <50% bootstrap support. Another result of systematic significance was the indication that subfamily Phytelephantoideae is related to two tribes from subfamily Ceroxyloideae, Cyclospatheae and Ceroxyleae.