Ecology, Biogeography and Pollen Morphology of Bienertia cycloptera Bunge ex Boiss. (Chenopodiaceae), an Enigmatic C4Plant without Kranz Anatomy

Abstract

Bienertia cycloptera is a most interesting terrestrial plant which applies C₄ photosynthesis without Kranz cells, but with dimorphic chloroplasts in one cell. In order to study this special quality and provide more information about the natural habitat of the species and probable evolutionary trends, we have examined the plant communities associated with B. cycloptera, the climatic conditions in which this species occurs, soil characteristics and pollen morphology in comparison with several other possible relatives. B. cycloptera is distributed around Central Iranian deserts and subdeserts with northern and southern radiation in the Persian Gulf countries and Central Asia, from 24° to 49° N latitude and from 43° to 67° E longitude. It grows in areas with mean daily temperatures between 20 and 30 °C during the hot months of the year, and annual precipitation of 400 to 76 mm (but mostly of 200 to 100 mm). B. cycloptera grows on high salty and temporarily moist clay soils with a salinity ranging from 21.7 to 89.6 ds/m, both in Na⁺ and SO₄^2- rich salty soils. In most plots, the percentage of C₄ species is over 50 % and in some cases 100 %. Climacoptera turcomanica is the most frequently associated species with B. cycloptera in most habitats. In order to look for further comparative data to find the affinity and evolutionary trends in Suaedeae and Salicornioideae, the pollen morphology of B. cycloptera, Borszczowia aralocaspica, Halopeplis pygmaea, Salicornia persica and six species of Suaeda, each representing one section, are compared by light and SEM microscopy. The pollen grains of B. cycloptera have the lowest pore number, with a mean of 42 pores per grain. The pore numbers of B. cycloptera are very close to Halopeplis pygmaea, a member of the tribe Halopeplideae of subfamily Salicornioideae. Among the studied Suaedeae, the pollen of B. cycloptera shows similarities with Suaeda physophora with regard to pore number and pore diameter. The affinity of B. cycloptera is a matter of discrepancy. Three different possible origins and relationships in Suaeda sect. Immersa, sect. Physophora, sect. Schanginia and tribe Halopeplidae are discussed. We conclude that the evolution, diversification and adaptation of Central and SW Asian halophytes is the result of intricate environmental and geological history of the area and needs intensive multidisciplinary research.