Cuticle Micromorphology of Caribbean and Central American Species ofPodocarpus(Podocarpaceae)

Abstract

The cuticle micromorphology of leaves of 13 species of Podocarpus (Podocarpaceae), nine from the Caribbean Islands and four from Central America, was studied with scanning electron microscopy. They include five of the seven species of section Pumilis (Podocarpus aristulatus, P. buchii, P. ekmanii, P. urbanii, and P. victorinianus), four of the seven species of section Nemoralis (P. guatemalensis, P. hispaniolensis, P. purdieanus, and P. trinitensis), three of the six species of section Lanceolatus (P. coriaceus, P. costaricensis, and P. matudae), and one of the three species of section Pratensis (P. oleifolius). The external and internal features of the adaxial and abaxial cuticles are described for all species and are compared with other known Podocarpus species (especially section Scytopodium). Leaves are hypostomatic, with stomata arranged in discontinuous rows parallel to the leaf axis. The external cuticles of all studied species possessed Florin rings. Stomatal plugs were observed in all species except P. buchii and P. costaricensis. The number of subsidiary cells varies from two to six, with two or three being most common. Polar subsidiary cells are constantly absent in seven species and present in six species, although in three of these, they are sometimes absent. The internal cuticle on subsidiary cell surfaces is smooth to slightly rugose and is sometimes pitted. The cuticle on guard cell surfaces is usually granular to rugose, sometimes with pits. Polar extensions occur in all species; they are thin in the studied species of section Pumilis but thick in those belonging to the other three sections. Epidermal cell outlines are straight to undulating. The cuticle on epidermal cell surfaces is rugose and pitted in all the Caribbean species except for P. trinitensis but much smoother to granular in P. trinitensis and the Central American species. The most useful characters to distinguish species are the micromorphology of the cuticle on guard cell surfaces, the presence or absence of polar subsidiary cells, the periclinal epidermal cell texture, and the epidermal cell shape and size. No synapomorphic characters of the leaf cuticle were found that supported any of the sections proposed in the 1985 revision of Podocarpus by de Laubenfels, but some qualitative characters were correlated with geographical distribution. Quantitative characters showed considerable variation between species, often providing distinguishing characters, but none of this variation was correlated either with the current taxonomic classification or with geography.