First report of subgenus Phoenicopsis (Czekanowskiales) from Middle Jurassic of Ordos,China and its paleoclimatic implications

Subgenus Phoenicopsis( Phoenicopsis) assigned to Czekanowskiales is recognized and a new species,Phoenicopsis( Ph.) ordosensis sp. nov. is first reported from the Middle Jurassic Yan'an Formation of the Ordos Basin,alternate based upon the leaf gross morphology and epidermal structures. The new species has linear leavs in bundles of five to six attached on a short shoot,more than 100 mm long by 5-6 mm wide,containing 10-12 parallel veins at upper portion. The leaf is hypostomatic. Epidermal cells are longitudinally arranged with smooth periclinal wall on the upper cuticle. The narrow non-stomatal zones and wide stomatal zones alternate in the lower cuticle. Stomata in four to five irregular spaced rows are longitudinally oriented in each stomatal zone.Guard cells for each are surrounded by four to five subsidiary cells with undeveloped papillae. Anticlinal walls of ordinary epidermal cells are nearly straight and periclinal walls slightly papillate. The new species shallow stomatal pits kept open and surrounded by unevenly undeveloped bulges. These characters are consistent with those of growth in a humid,rather than an arid climate. The presence of subgenus Phoenicopsis and other taxa of Czekanowskiales in the coal-bearing Yan'an Formation supports the view that the climate in the Ordos Basin was humid and warm with seasonal changes during the Middle Jurassic.