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Pollen of small-flowered neotropical Loranthaceae (8 genera; ca. 135 species) was examined in the light, scanning, and transmission electron microscopes. Pollen is typically medium-sized and oblate. Pollen amb is more variable than equatorial shape, ranging from trilobate deeply concave to circular. Both isopolar and heteropolar pollen grains occur within the complex, the latter restricted to species of Phthirusa and Struthanthus in which the apertures differ at each of the polar faces. Simple apertures arranged in a diploaperturate configuration predominate. Such apertures range from diploporate to diplobrevidemicolpate to diplosyn-and diploparasyndemicolpate types. Compound apertures are rare, restricted to Oryctanthus and particular species of Cladocolea and Struthanthus. The (3-)4-5 colpate apertures of Ixocactus are unique in the family. Sculpturing is basically uniform with sculpturing elements ranging from perforations to shallow ridges and/or striato-rugulae. Ultrastructurally, the basic ektexine structure is composed of a thin, perforate tectum, granular/columellate interstitium, and a thick continuous foot layer usually twice as thick as the tectum plus interstitium. Pollen data suggest two basic groupings of small-flowered genera: Group I, composed of Dendropemon, Phthirusa pro parte, and Oryctanthus', and Group II, containing Phthirusa pro parte, Cladocolea, Struthanthus, Maracanthus, and Oryctina. Among Group I genera, Dendropemon is closely linked to Phthirusa through the species P. pyrifolia and P. platyclada. Oryctanthus is a highly derived genus with only remote ties to other Group I taxa. Among Group II genera, pollen data indicate a close relationship between Cladocolea and the Mexican species of Struthanthus. Pollen characters of Ixocactus indicate no relationship with any small-flowered neotropical genus. Rather its pollen features are closer to those of the Eremolepidaceae and the African species of Viscum.In a previous paper we detailed the pollen of also shows a marked tendency towards unisexual the large-flowered neotropical Loranthaceae flowers and dioecism. Only three of the eight (Feuer & Kuijt, 1980). The present paper focuses genera exhibit strictly bisexual flowers {Oryctanon pollen characters of the small-flowered gen-thus, Dendropemon, Ixocactus)', two genera era. Data from these two complexes will be used (Phthirusa, Cladocolea) include some species with to analyze pollen evolution among neotropical strictly bisexual flowers and others with exclu-Loranthaceae. sively unisexual flowers; three genera {Struthan-The small-flowered neotropical complex com-thus excluding S, panamensis, Maracanthus, prises eight genera: Struthanthus (ca. 50 spp.), Oryctina) demonstrate only unisexual flowers. Cladocolea (ca. 25 spp.), Phthirusa (ca. 30 spp.), Small flower size, the tendency towards unisex-Dendropemon (ca. 12 spp.), Cladocolea (ca. 25 ual flowers and dioecism, and an .v = 8 chrospp.), Phthirusa (ca. 30 spp.) Dendropemon (ca. mosome number (Barlow & Wiens, 1971) to-12 spp.), Oryctanthus ...

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The parasitism of the mistletoes of the Americas is surveyed and integrated with recent observations on haustorial structure and mode of attack of the mistletoes of Central America and California. The occurrence and behavior of epicortical roots is traced in the genera Struthanthus, Phthirusa, and Antidaphne. Special consideration is given to the gross structure and development of the primary haustorial contact. A final section deals with the parasitism of mistletoes on leaves, on other mistletoes, and on themselves.