Karyotype polymorphism in the cycad Zamia loddigesii (Zamiaceae) of the Yucatan Peninsula, Mexico

Abstract

The cycad %amia loddigesii Miq. forms a morphologically variable complex on the Yucatan peninsula, Mexico. Several diploid chromosome numbers have been found in the species: In= 17, 24, 25, 26 and 27. Differing karyotypes and chromosome numbers were found in individuals of the same population and die karyotypes differ widely in numbers of metacentric and telocentric chromosomes present. Centrometric fission as well as pericentric inversions and unequal translocations are suggested to be the probable mechanisms for this karyotype variation. There appears to be a correlation between high chromosome number and increasing dryness of the habitats. Coupled with the strongly asymmetrical karyotypes, this suggests that karyotype evolution in Z‐ loddigesii is recent.

Taxonomic revision of Zamia in Mega-Mexico

“…Plants from its full biogeographic range, which would include El Salvador and Guatemala, were not available for this study. A modified root-tip squash method was used for examining somatic metaphase cells described by Vovides (1983) with a 12 to 15 hour icewater (0°C) follow-up soak after the 0.2% colchicine pretreatment at ambient temperature (Schutzman et al, 1988). Counts were made from the best 10-15 metaphase cells and karyotype noted according to the classification of Schlarbaum and Tsuchiya (1984).…”

“…In this context, we consider that a more extensive and detailed sampling of the genus Zamia across the Neotropics would be necessary to corroborate any correlation between trichome morphology and stem habit. REPRODUCTIVE STRUCTURES.-Although the characters employed for the identification of species of Zamia have been obtained from leaf morphology (Miquel, 1861(Miquel, , 1869Regel, 1857Regel, , 1876de Candolle, 1868;Schuster, 1932;Eckenwalder, 1980;Vovides et al, 1983;Newell, 1986;Schutzman & Vovides, 1998;Schutzman et al, 1988;Stevenson, 1993Stevenson, , 2001aStevenson, , b, 2004Nicolalde-Morejón et al, 2008), the evaluation of reproductive characters, especially those corresponding to ovulate strobili, is essential to discriminate among closely related taxa. Outstanding attributes that should be considered in this case are (i) the form and shape of the cone apex (Stevenson, 1987); (ii) the peduncle position with respect to the vertical axis of the cone, when mature (Schutzman et al, 1988); and (iii) the overall color of the cone (see descriptions and Figs.…”

“…CHROMOSOME NUMBERS.-Zamia shows the highest chromosome numbers and karyotype variation throughout the order Cycadales, with 2n counts of 16, 17, 18, 22, 23, 24, 25, 26, 27, and 28 (Marchant, 1968;Norstog, 1980Norstog, , 1981Vovides, 1983;Moretti & Sabato, 1984;Moretti, 1990a, b [VOL 61 Olivares, 1996). In contrast, all Ceratozamia species studied so far have stable diploid chromosome numbers (2n=16) and karyotypes, as do all the Dioon species analyzed to date with stable diploid chromosome numbers (2n=18) and karyotypes (Marchant, 1968;Vovides, 1983Vovides, , 1985Moretti, 1990a, b).…”

“…Its northern range starts in Georgia and Florida (U.S.A.), reaching Bolivia and the Mato Grosso of Brazil in South America (Balduzzi et al, 1982;Sabato, 1990;Norstog & Nicholls, 1997;Stevenson, 2001a, b). A remarkable morphological and cytological variation has been documented (Vovides, 1983;Moretti & Sabato, 1984;Moretti, 1990a, b;Stevenson et al, 1995Stevenson et al, -1996aVovides & Olivares, 1996;Norstog & Nicholls, 1997), and also high levels of genetic variation (González-Astorga et al, 2006). As a consequence of this complexity, the taxonomy of Zamia is controversial; although the genus comprises 75 species, their circumscription and limits have yet to be determined (Hill et al, 2007).…”

“…During the 19th century, six species were subsequently described for Mexico; Z. fischeri Miq., Z. katzeriana (Regel) Rettig, Z. lawsoniana Dyer, Z. loddigesii Miq., Z. spartea A. DC. and Z. verschaffeltii Miq., whereas the remaining known species were documented and characterized during the 20th century, with a marked tendency for taxonomic activity during the last thirty years (Vovides et al, 1983;Schutzman et al, 1988;Stevenson et al, 1995Stevenson et al, -1996aSchutzman & Vovides, 1998;Vovides, 1999).…”