Wood and Bark Anatomy of the New World Species of Ephedra

Quantitative and qualitative data are presented for wood of 42 collections of 23 species of Ephedra from North and South America; data on bark anatomy are offered for most of these. For five collections, root as well as stem wood is analyzed, and for two collections, anatomy of horizontal underground stems is compared to that of upright stems. Vessel diameter, vessel element length, fiber-tracheid length, and tracheid length increase with age. Vessels and tracheids bear helical thickenings in 10 North American species (first report); thickenings are absent in Mexican and South American species. Mean total area of perforations per mm2 of transection is more reliable as an indicator of conductive demands than mean vessel diameter or vessel area per mm2 of transection. Perforation area per mm2 is greatest in lianoid shrubs and treelike shrubs, less in large shrubs, and least in small shrubs. Plant size is roughly proportional to ecology, and thus perforation area per mm2 is indicative also of ecology. Growth rings are not marked in lianoid or tropical or subtropical species. Latewood has few or no vessels (and thus offers maximal conductive safety) in species from colder and drier habitats. The ecology of the species range from dry to extremely dry habitats. Rays are mostly wide multiseriate, but three tropical or subtropical species have uniseriate rays plus narrow multiseriate rays-possibly a primitive condition. The fiber-tracheids (parenchyma of other authors) are nucleated, and are considered a result oftracheid dimorphism phylogenetically. Tracheids are vaguely storied in a few species. Minute calcium oxalate crystals cover outer surfaces of wood ray cells, phloem ray cells, sieve cells, and phloem parenchyma abundantly in most species; the crystals are slightly less abundant on vessel, tracheid, and fiber-tracheid surfaces (first report of these crystals on these cell types). Crystals, tannins, and five types of sclerenchyma in bark are considered types of herbivore deterrents. Bark of some species is richer in these features; other species are poor in sclerenchyma or tannins or both. Independent evolution of vessels in Gnetales and angiosperms is briefly discussed