The Evolution of Parasitism in Scrophulariaceae/Orobanchaceae: Plastid Gene Sequences Refute an Evolutionary Transition Series

Abstract

TRANSITION SERIES'probably is not.Clade-ol paia-ilie genera correspond mil uilh hiogeogiaphie Parasitic angiospemis arc found in 16 families encountered.The group with the greatest range in and live in divers.' habitats, ranging horn tropical parasitic specialization is found within the Scroforests to arctic islands (Musselman & Press.phulaiiaceae/Orohanchaceae.This family pair in-1995).Recent work on several parasitic groups has eludes nonparasites, both facultative and obligate explored their analoim.ph\>iolngv.colngv.and hemiparasiles Iphotosynlhetic plants that obtain molecular biology and tin-control of economically water, nutrients, or photosv nlh.itcs from their host), srgmlicarit parasites (IVess ci (, raves, 1995).Par-and hoi, .parasitesinoii-photosynthetic, obtaining all asites exhibit dramatic adaptations.Some lack photosynthates from their host).Much has been leaves, stems, roots, and the al.ilih to pho(os\ ,,thc-learned about the aualomv and physiology of parsize.For many lineages of non-photosynthetic par-asitism in this group, cspec iall\ in Striga Lonrciro asites, study of their evolution is impeded hv the and Ombunchc L. which are important pests of very fact that they are so specialized and so differ-crop plants (Press & Graves.1995).Reliable inent from their nearest ph,.|o-\nthelie relatives.In formation on phylogeiieti, ivlat -hip-an g the many cases the idenlitv ol those relatives remains various nonparasites, hemiparasiles, and holoparunknown (Nickrent & Duff, 1996; Nickrent et al., asites would enable us to better understand the an-1998).The evolution of parasitism can best be atomical, physiological, and genetic changes that studied in a group where near relatives are known, occur during the evolution ,.| parasitism and the and different degrees of parasitic specialization are loss of photosynthetic ability. 1