Fig. 3

Comparative morphology and bract anatomy of Ephedra tweediana seed cones at three developmental stages: A green (Stage 1); B red (Stage 2), and C fleshy (Stage 3). White arrows show the papyraceous lateral region of the bracts (br); two seeds (s) are present per cone. D Cross section of a green bract stained with toluidine blue O and PAS showing a homogeneous mesophyll consisting of cells with substantial amounts of insoluble carbohydrates (*) and cellulosic fibers (black arrows) distributed in a single adaxial subepidermal layer. E Detail of vascular bundle in D, with mesophyll cells with substantial amounts of insoluble carbohydrates, phloem (p), xylem (x) and transfusion tissue (t). F Detail of mesophyll cell stained with PAS showing its vacuole filled with insoluble carbohydrates. G Overview of a red bract in cross section showing an increase in the number of cellulosic fiber layers (black arrows). H Detail of the vascular bundle shown in G, with adaxial epidermal cells (e) filled with phenolic compounds (tannins), and cellulosic fibers organized into one or two subepidermal layers (black arrows). I Polarized light microscopy showing the intense birefringence of cellulosic fibers in cross section (white arrows). Inset, detail of cellulosic fibers showing intense PAS staining on primary walls (arrowheads) and weak staining on secondary walls (black arrow). Adaxial epidermis (e) with thickening of the external and internal periclinal walls (arrowheads). J–L Cross section of fleshy bracts (Stage 3). J Cellulosic fibers (black arrows) are organized in separate bundles of one or two layers beneath the adaxial epidermis. Mesophyll cells are large with thin, sinuous walls and devoid of cytoplasmic content. Inset: polarized light microscopy showing the intense birefringence of cellulosic fibers (white arrows) and xylem. K Detail of the vascular bundle area beneath the adaxial epidermis with cellulosic fibers (black arrows) above, phloem, xylem and transfusion tissue. L Detail of papery lateral region of the bract, consisting solely of epidermis, with adaxial cells collapsed and reduced to the periclinal, juxtaposed walls (black arrows) and abaxial epidermis (eb) with tanniniferous cells. Scale bars: 1 mm (A–C); 100 µm (D, E, G, J–L); 50 µm (I); 20 µm (F)