Leaf epidermal structure of extant gnetales (Gnetum L.) and the Middle Jurassic bennettitales (Nilssoniopteris Nathorst and Ptilophyllum Morris)

The leaf epidermis of four species of Gnetum L. and four species of the Jurassic Bennettitales (Nilssoniopteris Nathorst and Ptilophyllum Morris) were studied. In addition to the description of qualitative characters, the analysis of various quantitative characters was carried out using statistical methods. Coefficients of variation for quantitative characters of the epidermal structure in Gnetum range from 6.4 to 24.0%, in Ptilophyllum from 15.7 to 63.5%, in Nilssoniopteris from 18.0 to 39.9%. The sinuosity of tangential cell walls of the epidermal cells in the upper and lower epidermis is the stable character in both groups of plants (Cv ≤ 18.0%). In Ptilophyllum and Gnetum, the length of stomata demonstrates a low level of common variability (Cv ≤ 16.8%). A significant range in the coefficients of variation in both Gnetum and the studied genera of Bennettitales is typical for the number of epidermal cells per 1 mm2 of the upper and lower epidermis (17.5% ≤ Cv ≤ 31.9%), the area of the epidermal cells of the upper and lower epidermis (21.2% ≤ Cv ≤ 63.5%), and the number of stomata per 1 mm2 of the epidermis (29.3% ≤ Cv ≤ 39.9%). The similarity in the correlation structure of epidermal characters is manifested in the correlation between sinuosity of tangential cell walls of epidermal cells, the number of stomata per 1 mm2 of the epidermis, and size of epidermal cells, as well as between the length of the stomata and the number of epidermal cells and also between the stomatal index and the number of cells in epidermis. In Gnetum, the ratio of the number of differentiated stomata correlates with the number of aborted stomata per 1 mm2 of epidermis. In N. angustifolia and P. caucasicum, the number of stomata correlates with the number of papillae per 1 mm2.