MCPHERSON, MARC A.* and SEAN W GRAHAM. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9. - Inference of Asparagales phylogeny using a large chloroplast data set.
The order Asparagales (sensu APG 1998) is pivotal to our current
understanding of monocot taxonomy and phylogeny. Recent morphological
and molecular analyses have provided major new insights into its
circumscription and internal phylogenetic structure, but various
aspects of its evolutionary history remain elusive or poorly
supported. To address further the higher-order relationships within
Asparagales, we examined chloroplast sequence data from 15 families
chosen to exemplify the phylogenetic diversity of the order
(Agavaceae, Alliaceae, Amaryllidaceae, Anthericaceae, Aphyllanthaceae,
Asparagaceae, Asphodelaceae, Boryaceae, Convallariaceae,
Hyacinthaceae, Iridaceae, Laxmanniaceae, Orchidaceae, Phormiaceae and
Tecophilaeaceae). Eight disjunct locations in the chloroplast genome
were sequenced (spanning 17 chloroplast genes, three introns and three
slowly evolving intergenic spacer regions), providing a total of 15 kb
(unaligned) of DNA sequence data per taxon. Outgroup taxa included
representatives from the other major monocot lineages. A
parsimony-based phylogeny inferred from these data was largely
congruent with previous studies, within the limits of current taxon
sampling. Bootstrap analysis (performed under the Fitch parsimony
criterion) provided moderate to strong support for most of the tree.
The order’s monophyly was strongly upheld, as was its division into a
lower Asparagales grade and a higher Asparagales clade, as indicated
by Chase et al. (1995) and Rudall et al. (1997). The family
Hyacinthaceae was indicated as the sister taxon of the distinctive
monotypic family Aphyllanthaceae. Alliaceae and Amaryllidaceae were
supported as sister taxa. Boryaceae and Orchidaceae were weakly
supported as sister taxa; Boryaceae-Orchidaceae was the sister-group
of the remaining Asparagales. In addition to addressing relationships
within the order, we briefly discuss the identity of the sister-group
of the Asparagales. We also discuss the molecular evolution of the
regions examined, providing evidence of intron loss and gene
deactivation in Asphodelaceae and Orchidaceae, respectively.
Key words: Asparagales, chloroplast phylogeny, intron deletion, Orchidaceae