Characterization and macropattern of calcium oxalate phytoliths in Argentinean endemic species of Chenopodioideae (Amaranthaceae)

PÉREZ CUADRA, V.; HERMANN, P.

Mar del Plata, Rep. Argentina

Congreso; 7th Internacional Meeting on Phytolith Research (7IMPR) y 4º Encuentro de Investigaciones Fitolíticas del Cono Sur; 2008

Society for Phytolith Research y Grupo de Estudios Fitolíticos Aplicados del Cono Sur

The subfamily Chenopodioideae comprises species with a worldwide distribution, although most of them are confined to xeric or saline areas. Calcium oxalate crystals are abundant in these species in the form of large aggregates as well as crystal sand; frequently both forms coexist within a single leaf. Crystals in the shape of octahedrons or prisms are infrequent. Mature leaves of Atriplex undulata, Nitrophila australis and Suaeda divaricata were collected in Salitral de la Vidriera (Prov. Buenos Aires), killed and fixed in FAA and processed using common techniques for anatomical studies and crystal macropattern identification. Cross sections of leaves of A. undulata show that crystals occur subepidermically in the chlorenchymatic tissue, frequently within idioblasts. In S. divaricata they occur deeper in the mesophyll. In N. australis, crystals are seen within the acquaeous tissue surrounding the vascular bundles. Only A. undulata has two types of crystals: druses and prisms. The arrangement of the crystals in the druses may differ: pyramids or inverted pyramids, whereas druses of the other two species are formed by non inverted pyramids. In cleared leaves of A. undulata and N. australis crystals can be observed in intercostal areas. In A. undulata druses formed by pyramidal crystals are the most abundant, occur at random in the whole lamina, and their size increases both acropetally and centripetally, whereas prisms and druses formed by inverted pyramids are found only towards the margins of the leaf and they do not show any great variation in size. A few small druses (with pyramidal crystals) occur at the base of the lamina but only close to the midrib. Druses in N. australis are located from the foliar margins to regions near the midrib; few of them are found in the apical zone. In S. divaricata they occur in the median region of the lamina, associated with minor veins. Crystal size varies. Druses: A. undulata 17-55 µm, N. australis 20-42 µm, S. divaricata 9-17 µm. Prisms (occurring only in A. undulata): 12-19 x 19-24 µm. The characterization of crystals and their macropatterns are useful for the identification of these species, which implies their taxonomic value. It is possible, however, that the amount of crystals in the three species might be related to the abundance of certain minerals in the soil or to seasonal variations in the environment, facts that have not been taken into consideration until recently.