In the last decade significant new information has been gained about the early evolution of flowering plants through studies of Early Cretaceous angiosperm pollen and the pollen of living primitive flowenng plants. Although most recent palynological studies of extant primitive angiosperms have used both scanning and transmission electron microscopy, few ultrastructural studies of early fossil aneioSDerm nollen erains pvict Thic r.an»r â"¢r^ro,o^«to « * * i.. ^li. _-^.._^.-tu:-* Cretaceous angiosperm Fredericksburgian of Ol yumupouennes nugnesii. two att. ClavatipoUenites species, Asteropollis asteroides. Stephanocolpites Jredencksburgensis, Retimonocolpites dividuus, R.peroreticulatm, two aff. Retimonocolpites species, StellatopoUis barghoornii, and three species of Liliacidites. These grains were investigated using a technique that we have developed for working with single fossil pollen grains by which we are able light-mic] known ' 7^ r""-" e^«x*xa, oui^ii aa muse luui cunsiiLuic me DUiK oi inc earuesi kiiuwu yai^. 01 the tossil record of the flowering plants, and provides a much improved means of deUmiting Early angiosperm pollen form uur study also reveals that a close similarity exists between some Early Cretaceous angiosperm pollen and pollen produced by certain living primitive angiosperms. ClavatipoUenites hughesii, Asteropollis asteroides, and Stephanocolpites fredericksburgensis exhibit varying degrees of similarity at the ultrastructural level respectively to pollen of the extant angiosperm genera Ascarina. Hedyosmum. and Chloranthus. all three of which belong to the modem family Chloranthaceae. Pollen described under

Pollen of the primitive angiosperm family Winteraceae has been discovered in the Aptian-Albian of Israel, extending the fossil record of this phylogenetically important family of flowering plants from the uppermost Upper Cretaceous back some 40 million years to the upper Lower Cretaceous. This appears to represent the earliest known record of a magnolialean angiosperm family and is convincing evidence for the existence in the Early Cretaceous of an extant family of angiosperms.

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Pollen of the American myristicaceous genera Compsoneura and Virola was studied with light, scanning electron, and transmission electron microscopy. Formal generic pollen descriptions are provided for each of these genera. Study of the pollen of these two genera reveals that they possess a number of similar palynological features, including sulcate apertures, reticuloid to reticulate exine sculpturing that sometimes consists of banded or beaded muri, a columellate interstitium with columellae frequently hanging from the tectum or only weakly attached to the nexine. and tectate-perforate to semitectate pollen grains. Pollen of Compsoneura, however, can be distinguished from that of Virola by (1) its nexine which is generally twice as thick as that in Virola, (2) its consistently more or less solid, nonlamellate nexine, and (3) its consistently inconspicuous intra-exinous, sexinous cavities. Within Compsoneura, pollen of section Coniostele is decidedly more advanced than that of section Compsoneura. Virola exhibits a wide range of exine sculpturing patterns, allowing recognition of three basic pollen types. Species of Pollen Type I have basically tectate-perforate grains although sometimes their pollen may be more or less reticuloid, and the exine surface or muri are usually psilate. Pollen Type II is characterized by tectate-perforate to semitectate grains which have banded to beaded muri, while Type III pollen grains are semitectate-reticulate with psilate muri. This is the fourth paper in a series dealing with the comparative pollen morphology of the family Myristicaceae. In previous papers we have already dealt with the pollen of the Madagascan (Walker & Walker, Grana, in press) and mainland African (Walker & Walker, Amer, J. Bot., 1, in press) genera of Myristicaceae, and with the American myristicaceous genera Dialyanthera, Iryanlhera, and Osteophloeum (Walker & Walker, Amer. 7. Bot., 2, in press). We are concerned in this paper with the pollen of the two remaining genera of American Myristicaceae â€" Compsoneura and Virola. We intend to examine the pollen of the Asian genera of Myristicaceae in subsequent papers.In the most recent revision of the American Myristicaceae, Smith (1938) recognized 8 species of Compsoneura and 38 species of Virola. Since then 2 additional species of Compsoneura and 9 more of Virola have been described, so that at present there are 10 species of Compsoneura and approximately 50 species of Virola. Compsoneura and Virola range from southern Mexico to northern South America, where most of their species occur.After the material and methods section, formal generic pollen descriptions are provided for both of the genera studied. This is followed by a discussion of the palynological features of these two genera, such as aperture type, exine sculptur-* We thank the directors of the following herbaria for allowing us to collect palynological material

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