188 



PHYLUM TRACHEOPHYTA: 



ORDER TAXALES (Yews) 



Diagnosis: known from Jurassic to Recent; gen- 

 erally large trees to about 90 feet tall and with bases 

 over 3 feet wide; commonly consisting of a straight 

 central axis above a branching root system, the trunk 

 scaly or fissured and the top half bearing branches 

 that often droop; lateral branches bearing spirally ar- 

 ranged, simple, entire, lanceolate, and stiflf parallel- 

 veined leaves, '/j inch to 3 inches long; without 

 typical cones; two to eight sporangia in a flower-like 

 arrangement; male sporangia normally stalked and 

 stamen-like, borne singly or in spike-like arrange- 

 ments in the leaf axils; female sporangia contribute to 

 ovule formation, but the general structure is only 

 vaguely pistil-like; seeds with a fleshy covering; plants 

 male or female (Figure 11.25). 



Figure 11.25 Yew types. Left, California nutmeg, Torreya colifornico. 

 Right, western yew, Taxus brevifolia. (Redrawn from Sudsworth.) 



Occurrence: about 15 species in 3 genera; Atislro- 

 laxus is limited to New Caledonia; Torreya has one 

 species in western Florida, one in California and 

 probably three in China and Japan; Taxus (yews) has 

 one western United States, one eastern United States, 

 and probably six other species, the genus being rep- 

 resented on all continents except South America and 

 Australia. 



ORDER GNETALES 



Diagnosis: composed of three genera, Cnetum, 

 Ephedra, and Welwilschia, probably only remotely re- 

 lated and not in the same order; angiosperm-like in 

 vein arrangement and (inetum with habit and leaves 

 like the Subclass Dicotyledoneae; no resins (found in 

 many gymnosperms); male and female cones com- 

 pound and flower-like (especially the male cone of 



Welwitschia); Gnetim reproduction involving a struc- 

 ture similar to an angiosperm embryo sac; embryos 

 with two embryo leaves, and leaves in opposite pairs. 

 Welwitschia, only one living species, is found in the 

 desert and semidesert areas of coastal southwestern 

 Africa. It is one of the truly strange plants, com- 

 posed of two large (to about 6 feet long), strap-like, 

 often apically frayed leaves inserted upon opposite 

 sides of the barely exposed part of the woody stem. 

 The barely exposed part of the stem is a concave disc 

 up to 4 feet in diameter; the disc margin bears many- 

 branched fertile shoots about 6 inches tall, each shoot 

 containing many cones. The underground stem is 

 long, large, and tuberous. Some plants apparently 

 live more than 100 years. 



Gnetum is represented by about 30 species in the 

 forests of the world's tropics. They are mostly climb- 

 ers, but a few are trees or shrubs. The leaves and 

 habits are much like those of certain climbing, shrub 

 or tree, dicot angiosperms. 



Ephedra contains about 35 species; generally cosmo- 

 politan in semidesert to desert areas. Most species 

 (including those in the United States) are twiggy, 

 often green-stemmed (young stems) shrubs with two 

 opposite, or three whorled, scale-like, inconspicuous 

 leaves at the nodes (Figure 11. 26). They may also be 

 tree-like or climbing. Plants are mostly male or fe- 

 male, cones compound and flower-like. 



Figure 11.26 Ephedra, the only United States genus of the Order 

 Gnetales (x ' 2). 



