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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Pollen of all large‐flowered neotropical loranthaceous genera and related Australian taxa (Nuytsia, Atkinsonia) were examined in the light, scanning, and transmission electron microscopes. Trilobate, deeply concave, peroblate or oblate pollen shapes are basic within the complex; triangular, slight convex, suboblate shapes are more derived features. The non‐fixiform pollen of Atkinsonia is unique within the family. Most of the large‐flowered genera possess exclusively syncolpate aperture types. However, among Psittacanthus species tricolpate, diplosynrugate and diplorugate apertures are also present, representing derived types for the complex. The inaperturate pollen of Atkinsonia appears to have developed independently within the family. Pollen sculpturing is typically non‐uniform, i.e., there are pronounced sculpturing differences in polar and equatorial regions. Uniformly sculptured pollen is restricted to Atkinsonia, Ligaria and some species of Psittacanthus. Ultrastructurally, most exine modifications have occurred in the equatoral ektexine. Here the basic organization ranges from essentially columellaless to columellate, the latter the more derived condition. Endexine is typically thick and stratified in polar areas, thin and lamellate in peripheral and apertural regions. Similar pollen morphologies of Nuytsia and Gaiadendron support the idea of a transoceanic evolutionary connection between the Old and New Worlds. Pollen characters show Gaiadendron to be the most primitive and Psittacanthus the most advanced among the large‐flowered neotropical genera.

An examination of pollen morphology and ultrastructure of Eremolepidaceae (Antidaphne, Ixidium, Eremolepis, Eubrachion) and Lepidoceras by light and scanning and transmission electron microscopy reveals a close relationship among the taxa. Pollen of Eremolepidaceae is typically echinate, tricolporate, and oblate-spheroidal. Eubrachion is unique within the family, exhibiting shallowly reticulate pollen. Ultrastructurally, all Eremolepidaceae exhibit a similar exine structure. The sculptural ektexinous elements (spines or 'muri') are never contiguous with the basal ektexine but rest on a thin granular zone. Pollen characters of Lepidoceras are particularly close to those of Ixidium and Eremolepis. The porate (por(or)ate) aperture type, completely spherical shape, and reduced granular ektexine of Lepidoceras pollen indicate an advanced position within the complex. The relationship of Tupeia to Eremolepidaceae is more obscure as pollen of the genus exhibits both eremolepidaceous (echinate sculpturing, shape in polar and equatorial views) as well as loranthaceous characters (simple apertures, ektexine organization). Palynologically Eremolepidaceae and related genera show no particular close relationship to Olacaceae or Santalaceae. Though Eremolepidaceae et al. do share a number of pollen features with Viscaceae (echinate sculpturing, compound apertures, exine organization) the strong nonpalynological differences between the two families suggest that these pollen features may have arisen independently.

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