Polyphyly of the tuberous Lomatiums (Apiaceae): CpDNA evidence for morphological convergence

Overlapping patterns of morphological variation in Lomatium have obscured interspecific relationships and thwarted attempts at infrageneric classification. However, the tuberous lomatiums, a group of 13 species mostly from the Inland Pacific Northwest of the U.S.A. and allied primarily by their thickened roots, have long been considered an informal assemblage in Lomatium, although they have received formal taxonomic recognition at the infrageneric level only once. Variation in root morphology is coupled with interspecific differences in leaf and fruit morphology, flower color, and involucel structure. To test the monophyly of the tuberous group and to examine patterns of relationship and morphological divergence among these species, a phylogenetic analysis was conducted using chloroplast DNA (cpDNA) restriction site variation. Samples of all taxa of tuberous lomatiums except the narrowly endemic L. stebbinsii were analyzed. Also included were samples of 18 other species of Lomatium, representing all but one of the morphological groups in the genus, and the related genus, Angelica. Phylogenetic trees of Lomatium were well resolved but generally weakly supported. The tuberous group is apparently polyphyletic, comprising members of at least four distinct lineages: 1) L. watsonii, associated with the L. columbianum group from the Pacific Northwest; 2) L. ambiguum, an apparent relative of several nontuberous species from California; 3) L. hendersonii, one branch of a speciose trichotomy and apparently only distantly related to other tuberous species, and 4) the remaining nine tuberous species sampled. Thus, within Lomatium, tuberous roots may have evolved in parallel several times. Developmental studies are needed to determine the mode of root thickening and the organogenesis of these storage structures.