Fig. 2

Comparative morphology and bract anatomy of Ephedra triandra seed cones at three developmental stages: A green (Stage 1), B red (Stage 2), and C fleshy (Stage 3). The white arrow shows a papyraceous lateral region that decreases as bracts (br) and seeds (s) mature. D Cross section of a green bract stained with PAS showing a continuous single layer of cellulosic fibers beneath the epidermis (black arrow), and a mesophyll of cells with substantial amounts of insoluble carbohydrates (*). Adaxial epidermis (e), xylem (x) and transfusion tissue (t). E, F Cross sections of red bracts stained with PAS and toluidine blue O, showing the proliferation of cellulosic fibers (black arrows) beneath the adaxial epidermis. Mesophyll cells (*) no longer contain insoluble carbohydrates. G Cross section of red and fleshy bracts showing an adaxial epidermis with columnar cells and cellulosic fibers organized in several subepidermal layers (arrows). Mesophyll cells (*) look enlarged, with thin primary walls and enlarged vacuoles. H Detail of the vascular bundle in G, adaxial epidermis, xylem and transfusion tissue. I Detail of cellulosic fibers (arrows) showing intense PAS staining on their primary walls (black arrows) and lighter staining on their secondary walls. Adaxial epidermis and transfusion tissue. J Polarized light microscopy showing the intense birefringence of cellulosic fibers in cross section (arrows). K Detail of the abaxial face showing the distribution of cellulosic fibers (arrows) in subepidermal layers. Mesophyll cells (*) are enlarged, with thin, sinuous walls and enlarged vacuoles in their cytoplasm. Scale bars: 1 mm (A–C); 100 µm (D); 50 µm (E, F, I–K); 100 µm (G, H)