Leaf micromorphology as a possible tool in cycads systematics
by Barone Lumaga M. R., Coiro M., Erdei B., Mickle J. (2012)
In Conference Botany 2012, Columbus, Ohio, USA, July 7–11, Abstract ID: 306 –
The genus Ceratozamia (Cycadales; Zamiaceae) was classically divided into two groups based on gross leaf morphology, but recent molecular phylogenetic analyses has identified three clades. On a larger scale, Ceratozamia appears closely related to Stangeria and to the neotropical genera Microcycas and Zamia. Whole leaf and isolated cuticle specimens from eight Ceratozamia species (C. euryphyllidia, C. hildae, C. kuesteriana, C. latifolia, C. matudae, C. mexicana, C. miqueliana, C. norstogii), Stangeria eriopus, Microcycas calocoma, and Zamia amblyphyllidia were examined using SEM for features of inner and external surfaces.
Samples were collected from the middle region of leaflets of mature leaves of greenhouse-grown plants. For external surfaces, samples were air dried or fixed in FAA (10:5:50) and critical-point dried. For the inner cuticle surface, isolated cuticles were obtained using 20% CrO3.
Characteristics in common to these species include hypostomy with the exception of S. eriopus showing stomata also on the adaxial side (near the midrib), occasional presence of hair scars, adaxial epidermal cells longitudinally elongated and arranged in rows, and smooth adaxial exterior cuticle (with the exception of S. eriopus showing irregular ridges).
Stomatal complexes are not contiguous and are oriented parallel to the leaflet axis (with the exception of S. eriopus showing randomly oriented stomata), and are of the diperigenous to tetraperiginous type in Ceratozamia species, M. calocoma and Z. amblyphyllidia, with S. eriopus showing stomata of polyperigenous type.
Lightly granulate epicuticular wax borders stomatal pits in M. calocoma and Z. paucijuga, and it is granulate in C. matudae and C. robusta.
Epicuticular wax occuring as granules to ridges borders the pits in C. euryphyllidia, C. miqueliana, C. norstogii and as reticulate ridges in C. hildae, C. kuesteriana, C. latifolia, C. mexicana.
The distribution of different kinds of epicuticular waxes in Ceratozamia species closely reflect the phylogenetic relationships that has emerged from molecular data. The presence of granulated wax in M. calocoma and Z. amblyphyllidia suggests that this character is ancestral in Ceratozamia.
The closeness of S. eriopus to the other taxa is not supported by cuticular micromorphology. The close correspondence between molecular and micromorphogical data in Ceratozamia confirms that micromorphology can provide useful data for rapidly and efficiently assessing systematics in other cycad taxa.