Leafy shoots and pollen cones of conifers from the Middle Jurassic deposits of the Irkutsk Coal Basin

Abstract

Among the numerous remains of the Jurassic conifers in the Irkutsk Coal Basin, several types of leafy shoots are distinguished. One type is characterized by the leaves with numerous veins. These remains were described as Podozamites irkutensis N. Nosova et Kiritch. (Nosova et al., 2017). The leaves of other types have a midvein. These leafy shoots are attributed to several taxa: Marskea sp. nov. (in press), Elatocladus falcatus (Heer) Prynada, E. heeriana N. Nosova et Kiritch., sp. nov., Elatocladus sp. and Pagiophyllum sp. Elatocladus falcatus (Heer) Prynada, 1962 (=Elatides falcata Heer, 1976) was described from the deposits of the lower subformation of the Prisayan Formation (the Aalenian) of the Ust’-Baley locality. An epidermal structure of the Elatocladus falcatus leaves is unknown. Here we designate the lectotype for E. falcatus. We have studied the leaf epidermal structure of the leafy shoots from the upper subformation of the Prisayan Formation (the Aalenian-Bajocian) in the localities Topka and Vladimirovka. Based on the morphological and epidermal features, we describe a new species Elatocladus heeriana. The shoots of E. heeriana have with helically arranged leaves. The leaves are sessile and dorsoventrally flattened, linear, lanceolate to falcate, with the tip curving toward the apex of the stem, with the broad and decurrent base and acute apex. The leaves are hypostomatic. They are characterized by straight to undulating anticlinal cell walls of the abaxial epidermis near the leaf edge and base. Stomata are arranged in two narrow bands, orientated transversely to irregularly. Subsidiary cells of the stomatal complexes are without papillae. Rare fragments of the Pagiophyllum sp. shoots were found in the deposits of the upper subformation of the Prisayan Formation (the Aalenian–Bajocian) in the localities Olkha and Vladimirovka. Their leaves are falcate, with a median keel on the abaxial side. The bad preservation of the cuticle did not allow us to study the epidermal pattern in details. Stomata are arranged in the bands, orientated irregularly. Subsidiary cells of the stomatal complexes are without papillae. One pollen cone (microstrobilus), attached presumably to the E. heeriana shoot, and several detached pollen cones of Schidolepium gracile Heer (1880) were found. The pollen cones are elongated, with numerous imbricate, helically arranged and dorsoventrally flattened microsporophylls. Sterile part of the microsporophyll expands to the distal lamina with acute apex. Some microsporophylls near the cone base are oval with rounded apex. The numerous microsporangia are visible in the apical part of the mature pollen cone, but a distal lamina of the microsporophylls often is indistinct here. Microsporangia (5–7 per microsporophyll) are elongated, fusiform. Pollen grains are spherical, nonsaccate, with the rugulate-perforate surface, apertures are invisible. The emended diagnosis is provided for the type species S. gracile, as well as the lectotype is designated.