干旱区生态环境知识资源中心

Plant fossils recently collected from the Middle-Late Triassic Madygen Formation in SW Kyrgyzstan, Central Asia are described in detail. Based on the combination of gross morphology and epidermal/cuticular anatomy, four different taxa are identified, assigned to the Cycadales, i.e. Pseudoctenis lanei and Bennettitales, Pterophyllum pinnatifidum, P. firmifolium and Otozamites sp. All taxa are new for the Madygen Formation. Remarkable is the first occurrence of Pseudoctenis and two Pterophyllum species in the Triassic of Central Asia. The fossils are generally well preserved, but without cuticles. Nevertheless, epidermal and cuticular features can be recognized because the cuticles left behind imprints in the very fine-grained matrix. Silicon casts, examined under a stereomicroscope and with SEM, revealed xeromorphic features that are traditionally considered as indicators of arid conditions. However, comparisons of the functionality of the xeromorphic features in living plants show that these features occur in xerophytic, as well as in hygrophytic and halophytic plants. Sedimentological data from Madygen show that the fossil flora grew in alluvial plains, delta plains, and shallow lacustrine environments. The xeromorphic features are consequently interpreted as functional adaptations to environmental influences involved in the self-cleaning of the leaf surface, regulation of excessive radiation and leaf temperature and as an effective mechanical defense against phytophagous insects. (C) 2010 Elsevier B.V. All rights reserved.