Wood, Bark, and Pith Anatomy of Old World Species of Ephedra and Summary for the Genus

Quantitative and qualitative data are presented for wood anatomy of 35 collections representing 22 Old World species of Ephedra; the survey of bark and pith anatomy is based on some of these species. Character-state ranges similar to those of the New World species are reported, although more numerous species show vessel absence in latewood. Little diminution in vessel diameter or density occurs in latewood of the eight species that are scandant or sprawling. Helical thickenings or sculpture occur in vessels of about a third of the Old World species, but these thickenings are clearly related to pits, often not very prominent, and rarely present in tracheids (alternative expressions characterize helical thickenings in the New World species). Helical thickenings are statistically correlated to xeromorphic wood features such as narrower vessels and fewer vessels per mm2 of transection. Paucity of vessels is an indicator ofxeromorphy (rather than abundance, as in dicotyledons) because tracheids, which have optimal conductive safety, are present instead of vessels. Near vessellessness is reported for E. distachya var. monostachya, E. gerardiana, and E. monosperma. A high degree of wood xeromorphy characterizes species of the highlands of Central Asia and the Middle East, where extremes of drought and cold prevail. A close approach to storied structure is reported in three species. Procumbent ray cells, absent at first, are produced as stems increase in diameter. Vessel element length also increases with stem size, and is not a phyletic indicator. Minute calcium oxalate crystals cover the outside of wood and bark cells, and suggest relationship to Welwitschia and perhaps conifers. A review of New World as well as Old World species reveals few species criteria, and these are mostly difficult to quantify. Primitive character states cannot be defined with certainty in the genus. Wood of Ephedra is like that of a vessel-bearing gymnosperm; parallelisms with dicotyledons may be caused by the vessel-bearing habit.