Microcycas

Abstract: Chromosome numbers and karyotypes of species from four American Zamiaceae (Cycadales) are reported. Zamia shows interspecific and intraspecific chromosome variation, whereas Microcycas, Ceratozamia, and Dioon have constant karyotypes within each genus. In Zamia, all karyotypes have the same number of submetacentric and acrocentric chromosomes, but they differ in the number of metacentric and telocentric chromosomes. Centric fission of metacentric chromosomes is proposed to explain the karyotypic variation in this genus. Zamia shows karyological relationships with Microcycas and Ceratozamia, whereas Dioon appears very distinct from the other American cycad genera. Affinity among Zamia, Ceratozamia, and Microcycas karyotypes and distinctiveness of Dioon karyotypes are supported by comparative analysis of phenotypic characters in the four genera. THE CYCADALES (cycads) are a group of ancient plants with gymnospermous reproductive biology whose fossils date to the Permian period (Mamay, 1976). They had worldwide distribution during the Mesozoic Era (Delevoryas, 1982), but today are represented by a few scattered taxa. Eleven genera with a pantropical distribution have survived (Johnson, 1959; Stevenson, 1989a). In the Neotropics, there are five genera in the Zamiaceae: Ceratozamia Brongn., Chigua D. Stevenson, Dioon Lindl., MicrocycasA. DC., and Zamia L. The genus Ceratozamia is composed of 11 species in Mexico, Belize, and Guatemala; Chigua has two species in Colombia; Dioon has ten species in Mexico and Honduras; the monotypic genus Microcycas is endemic to Cuba; and Zamia is composed of 40-45 widespread species in Florida, Mexico, the West Indies, and Central and South America (Balduzzi, De Luca, and Sabato, 1982; Eckenwalder, 1980; Sabato and De Luca, 1985; Stevenson, 1989a, b; Stevenson, Sabato, and Vazquez Torres, 1986). In recent years, many studies have been carried out on American cycad genera which have contributed to our ' Received for publication 20 October 1989; revision accepted 7 March 1990. The author thanks Dr. K. Norstog (Fairchild Tropical Garden, Miami), Dr. D. Wm. Stevenson (The New York Botanical Garden), and Dr. A. P. Vovides (Fairchild Tropical Garden) for suggestions, support, and valuable input throughout the research and preparation of this manuscript. Special thanks to Dr. J. Popenoe and staff at Fairchild Tropical Garden for all the facilities put at my disposal during repeated visits in Miami. knowledge of the numerous morphological, taxonomic, distributional, phytochemical, and reproductive features of these genera (Balduzzi et al., 1982; De Luca et al., 1982; Dehgan and Dehgan, 1988; Dossaji, Mabry, and Bell, 1975; Moretti, Sabato, and Siniscalco Gigliano, 1983; Moretti, Sabato, and Vazquez Torres, 1980; Norstog, 1989; Stevenson, 1981, 1989a; Vovides, Rees, and Vazquez Torres, 1983). This information has been utilized to elucidate tentative phylogenetic relationships among these genera (Crane, 1988; Stevenson, 1989a). Karyological studies can provide additional useful information in understanding the phylogeny of American cycads, but their use has been limited because karyotypic data on American Zamiaceae have been very incomplete. Karyotypes of a few species of Ceratozamia and Dioon have been described (Marchant, 1968; Sax and Beal, 1934; Vovides, 1983, 1985), and only a report on Microcycas is available (Sax and Beal, 1934). Zamia has been investigated more thoroughly. Unlike the other genera, Zamia shows diversity in chromosome number and karyotypes (Marchant, 1968; Norstog, 1980; Resende and Rijo, 1948; Schutzman, 1984; Schutzman, Vovides, and Dehgan, 1988; Vovides, 1983); in addition, two species, Z. roezli (previously reported as Z. chigua) (Norstog, 1981) and Z. paucijuga (Moretti and Sabato, 1984), show intraspecific chromosome variation. In the present paper, karyotypes of Zamia, Microcycas, Ceratozamia, and Dioon species are investigated and results are discussed in

Abstract: Chromosome numbers and karyotypes of species from four American Zamiaceae (Cycadales) are reported. Zamia shows interspecific and intraspecific chromosome variation, whereas Microcycas, Ceratozamia, and Dioon have constant karyotypes within each genus. In Zamia, all karyotypes have the same number of submetacentric and acrocentric chromosomes, but they differ in the number of metacentric and telocentric chromosomes. Centric fission of metacentric chromosomes is proposed to explain the karyotypic variation in this genus. Zamia shows karyological relationships with Microcycas and Ceratozamia, whereas Dioon appears very distinct from the other American cycad genera. Affinity among Zamia, Ceratozamia, and Microcycas karyotypes and distinctiveness of Dioon karyotypes are supported by comparative analysis of phenotypic characters in the four genera. THE CYCADALES (cycads) are a group of ancient plants with gymnospermous reproductive biology whose fossils date to the Permian period (Mamay, 1976). They had worldwide distribution during the Mesozoic Era (Delevoryas, 1982), but today are represented by a few scat

Abstract: A phylogenetic analysis of American cycad genera, all belonging to the family Zamiaceae, was attempted using chloroplast DNA restriction fragment polymorphisms.Ceratozamia mexicana Brongn.,Chigua restrepoi D. Stevenson,Dioon edule Lindley,Microcycas calocoma (Miq.) A. DC.,Zamia fischeri Miq., andZamia skinneri Warsz. ex A. Dietrich were used as representatives of the genera.Cycas revoluta Thunb., belonging to the family Cycadaceae, was used as an outgroup, following previous morphological works. One hundred and forty-one shared restriction fragments were scored for presence/absence and both Wagner and Dollo parsimony analyses were performed. The single, fully resolved, most parsimonious trees obtained from the analyses were topologically identical and perfectly matched previous morphology-based phylogenetic hypotheses. Statistical evaluation of the data showed a good reliability for the obtained phylogeny.Dioon edule, belonging to a different subfamily and more primitive on morphological grounds, proved to be the most primitive among American cycads as inferred from the molecular data;Chigua restrepoi, never analyzed before on cladistic grounds, was found to be the sister group of the genusZamia.