A phylogeny of all species of Arceuthobium (Viscaceae) using nuclear and chloroplast DNA sequences

Abstract

The genus Arceuthobium (dwarf mistletoes, Viscaceae) comprises 42 species that parasitize hosts in Pinaceae and Cupressaceae in the Old and New Worlds. Maximum parsimony analyses were conducted on two data partitions (separately and combined): nuclear ribosomal internal transcribed spacer (ITS) sequences for all 42 currently recognized species and chloroplast trnT-L-F sequences for 34 New World species. The Old and New World species were phylogenetically distinct using ITS, thus making subgenus Arceuthobium paraphyletic. Arceuthobium pendens and A. guatemalense comprise the basalmost clade of subgenus Vaginata, characterized by the presence of flabellate secondary branching. The trnT-L-F sequences, which vary widely in length depending upon taxon, contain three times less phylogenetic signal than ITS, although homoplasy for this partition is lower. Several of the clades obtained from analysis of nuclear ITS sequences are also recovered using trnT-L-F sequences such as A. guatemalense and A. pendens, the A. rubrum group, the A. vaginatum group, and the A. campylopodum group. The ITS + trnT-L-F tree is well resolved except for four internal nodes. A revised classification of the genus is discussed that recognizes only monophyletic species that are well differentiated by molecular data.

Mistletoes: Pathology, Systematics, Ecology, and Management

“…It was proposed (91,92) that this mistletoe could be primitive (i.e., evolved early in the history of the genus) and was thus the "link" to other members of Viscaceae that have nondehiscent fruits. The topology of the molecular phylogenetic tree clearly showed that this was not the case (152). The ancestor of A. verticilliflorum had an explosive fruit, but this feature was lost sometime during the evolution of the modern species.…”

“…The first molecular phylogenetic investigation of interspecific relationships in dwarf mistletoes was by Nickrent et al (154) using ITS sequences. A second more detailed study included all currently recognized species in the genus and added chloroplast (trnL region) sequences to the ITS data (152). That study showed that the Old and New World species were genetically distant, so much so that primers for the trnL region did not work with the Old World taxa.…”

Prophyll, calyculus, and perianth in <I>Santalales</I>

“…& Wiens, an endemic to the Azores, is said to be "crucial to an understanding the migrational history of the genus" (Nickrent et al 2004). The species is also characterized by verticillate branching, as are the related A. oxycedri (DC.)…”

Viscaceae

“…Forty-two spp. (according to Nickrent et al 2004); one sp. on Hispaniola, and one on the Azores; various spp.…”

“…Curiously, in the rare instances that these mistletoes become established on uncongenial hosts, as in A. americanum on Picea engelmannii, an anisophasic broom develops; the symptomatolgy has changed radically. Isophasic parasitism in Arceuthobium likely evolved independently more than once, as suggested by its documented occurrence in both subgenera and four sections recognized by Nickrent et al (2004). In addition to the remarkable Mexican Phoradendron perredactum that has recently been described (Kuijt 2011;Rzedowski and Calderón de R. 2011), parallels to this mode of parasitic behavior have evolved independently in some holoparasitic plants in Apodanthaceae (Pilostyles haussknechtii) and Mitrastemonaceae (Mitrastemon) (Kuijt 1960).…”