In this paper we present the first embryological studies of Alzatea, one of the genera of the order Myrtales whose placement has been most controversial. Although Alzatea agrees rather completely with the other Myrtales in its basic embryological characteristics, it stands apart from all other members of the order that have been examined in having a bisporic Allium-type embryo sac. Comparisons with related groups, including Axinandra, Rhynchocalyx, Lythraceae, and Melastomataceae, indicate that Alzatea shares many more characteristics with Rhynchocalyx than with the others. Among the groups mentioned, only Alzatea and Rhynchocalyx coincide in their micropyle form, and both genera further agree with Lythraceae in the multi-celled ovule archesporium, which is not known elsewhere in the order except in one of the small subfamilies of Lythraceae, Sonneratioideae. A totality of similarities and dissimilarities with the other Myrtales favors the establishment of a monotypic family, Alzateaceae, and suggests that Alzatea and Rhynchocalyx may be parallel descendants from a common ancestor, with which the modem Lythraceae possibly has a link. This paper deals with the embryology of the rare monotypic Central-South American genus, Alzatea, and is the third concerning the unique genera of the order Myrtales, following papers on Axinandra (Tobe & Raven, 1 983b) and Rhynchocalyx (Tobe & Raven, 1984). As in the case of Axinandra and Rhynchocalyx, there has been a long history of arguments about the taxonomic position ofAlzatea. According to Lourteig (1965), who gave a historical review up to that time, Alzatea has been placed in Celastraceae (De Candolle, 1825; Bentham & Hooker, 1862), Rhamnaceae (Miers, 1872; Loesener, 1942; MacBride, 1951), and Lythraceae (Planchon, 1845; Hallier, 1911; Pilger, 1915). Lourteig (1965) herself concluded that Alzatea belonged in Lythraceae, based on its floral and vegetative characters as well as on anatomical and palynological characters. She considered the genus to be a member of subtribe Diplusodontinae of tribe Lythreae. At other times in its history, Alzatea has been considered to have a close affinity with another unique genus, Crypteronia, regardless of the family to which Crypteronia was assigned at that time (Miers, 1872; Loesener, 1942). Recently, van Beusekom-Osinga and van Beusekom (1975) proposed broadening the definition of Crypteroniaceae to include Alzatea together with Crypteronia, Dactylocladus, Axinandra, and Rhynchocalyx. Muller (1975) suggested a possible relationship among these five genera based on their pollen morphology. But van Vliet (1975), van Vliet and Baas (1975), and Baas (1979), on the basis of their studies of the wood, leaf, twig, and nodal anatomy, suggested not only that Alzatea and Rhynchocalyx differed widely from the three other genera of Crypteroniaceae sensu lato, but also that these two genera differed to a substantial degree from each other. Dahlgren and Thorne (1984) and Johnson and Briggs (1984), accepted the establishment by S. Graham (1984) of a monotypic family, Alzateaceae. Results of our recent embryological studies have indicated that Axinandra and Rhynchocalyx are very different from each other, and that the former occupies a satellite position to Melastomataceae (Tobe & Raven, 1983b, 1984). Rynchocalyx is of less certain placement, but probably deserves the family status that it was accorded by Johnson and Briggs (1984). We carried out the present study of the embryology of Alzatea, which has hitherto been unknown, as a contribution to determining its most appropriate systematic position. MATERIALS AND METHODS The only species of what is probably a monotypic family, Alzatea verticillata Ruiz & Pav., ' Grants to one of us (P. H. R.) from the National Science Foundation are gratefully acknowledged for financial support. We are also grateful to Miss Sandra Knapp and Sr. Luis Poveda for the collection of the fine material on which our study is based. 2 Permanent address: Department of Biology, Faculty of Science, Chiba University, 1-33 Yayoi-cho, Chiba 260, Japan. 3 Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166. ANN. MISSOURI BOT. GARD. 71: 844-852. 1984. This content downloaded from 157.55.39.215 on Tue, 30 Aug 2016 05:37:47 UTC All use subject to http://about.jstor.org/terms 1964] TOBE & RAVEN-EMBRYOLOGY OF ALZA TEA 845