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* Speciation via race formation is an important evolutionary process in parasites, producing changes that favour their development on particular host species. Here, the holoparasitic plant Cytinus, which has diverse host species in the family Cistaceae, has been used to study the occurrence of such races. * Amplified fragment length polymorphism (AFLP) analyses were performed on 174 individuals of 22 populations parasitizing 10 Cistaceae species in the Western Mediterranean basin. * Neighbour-joining, multivariate ordination analyses, and individual-based Bayesian analyses, clustered Cytinus populations into five well-characterized genetic races that, overall, agreed with the taxonomic sections of their hosts. In the AMOVA, among-races differences accounted for almost 50% of the genetic variation. The isolation-by-distance model was not supported by a Mantel test among Cytinus populations (r = 0.012; P = 0.456). All races showed low within-population genetic diversity, probably as a result of restricted pollen flow aggravated by flowering asynchrony, restricted seed dispersion, or stochastic processes. * The genetic differentiation among the five races of Cytinus is congruent with the view that these races are well-characterized lineages that have evolved independently as a result of selective pressures imposed by their hosts. This pattern, with genetically distinctive groups associated with the infrageneric sections of the host species, has not been reported previously for parasitic angiosperms.

In a recent study (American Journal of Botany 97: 730-737), we described the first case of a tripartite association in natural conditions among a holoparasitic plant (Cytinus), its host Cistaceae species, and mycorrhizal fungi at an anatomical level. In a letter to the editor, Brundren (American Journal of Botany 98: 595-596) commented on our manuscript and questioned our conclusions, arguing that they are not adequately supported by the data. We reject this point of view and believe that the controversy has arian because of the parasitic way of life of Cvthzus. We maintain and demonstrate that there is enough evidence in the data that we presented to confinn the existence of mycorrhizal associations in the Cytinus-Cistaceae complex, supporting the functionality of the tripartite association. Most holoparasitic plants have been considered as nonmycorrhizal. However, it is not advisable to be categorical in drawing conclusions about the mycorrhizal status of a group of plants that has not been fully studied. [ABSTRACT FROM AUTHOR]

Mycorrhizae are widespread mutualistic symbioses crucial for the functioning of terrestial ecosystems. Not all plants associate with mycorrhizae; most parasitic plants have been siggested to be nonmycorrhizal because they have developed alterantive strategies to obtain nutrients. In endophytiv parasitic plants, whose vegetative bodies grow completely inside their mycorrhizal host roots, the opportunity for establishing a tripartite association seems evident, but information on these systems is lacking. In studying natural associationc among hte endophytic holoparasite Cytinud hypocistis, their Cistaceae host species, and associated mycorhizal fungi, we found that mycorrhizae were associated wiht the hosts and the parasires, reaching high frequencies of colonization. In parasitic and host root tissues, mycorrhizal fungi spread in the parenchymatic cells by intracellular growth and formed hyphal coils and vesicles, while the cambium and the vascular tissues were never colonized. This report is the first on a tripatite association of an endophytic parasitic plant, its host, and nycorrhizae in natural conditions, representing a novel trophic interaction not previously reported within the angiosperms. Additional studies on the interactions occuring among these three players are needed because they may be crucial to our understanding of how this mutualistic – antagonistic system is functioning and evolving. [ABSTRACT FROM AUTHOR]

Mycorrhizae are widespread mutualistic symbioses crucial for the functioning of terrestial ecosystems. Not all plants associate with mycorrhizae; most parasitic plants have been siggested to be nonmycorrhizal because they have developed alterantive strategies to obtain nutrients. In endophytiv parasitic plants, whose vegetative bodies grow completely inside their mycorrhizal host roots, the opportunity for establishing a tripartite association seems evident, but information on these systems is lacking. In studying natural associationc among hte endophytic holoparasite Cytinud hypocistis, their Cistaceae host species, and associated mycorhizal fungi, we found that mycorrhizae were associated wiht the hosts and the parasires, reaching high frequencies of colonization. In parasitic and host root tissues, mycorrhizal fungi spread in the parenchymatic cells by intracellular growth and formed hyphal coils and vesicles, while the cambium and the vascular tissues were never colonized. This report is the first on a tripatite association of an endophytic parasitic plant, its host, and nycorrhizae in natural conditions, representing a novel trophic interaction not previously reported within the angiosperms. Additional studies on the interactions occuring among these three players are needed because they may be crucial to our understanding of how this mutualistic – antagonistic system is functioning and evolving. [ABSTRACT FROM AUTHOR]