178 



PHYIUM TRACHEOPHYTA: 



Figure 11.12 Equiseium. A-E, Equhetum arvense, a horsetail; A, 

 fertile shoot (x '"'4); B, sterile shoot (x 1 ' 2): C, cone (x 1 ' ■2); D- sporan- 

 gium-bearing unit of a cone (x 18); E, part of the stem {x 2' -j). F, f. 

 hiemale, o scouring rush (x /<;); I.S., leaf sheath; r., rhizome; s., sporan- 

 gium. (Used by permission, from Arthur Cronquist, Introductory Botany, 

 Harper, New York, 1961.) 



rhizome; regularly are short, simple, or with a few 

 branches. 



Reproduction : living and most known fossil species 

 produce a single type of spore; a few fossils had two 

 types of spores; single-spore species develop a multi- 

 cellular gametophyte with both sex organs, an organi- 

 zation typical of all such reproductive types; gameto- 

 phyte commonly a membranous, cushion-shaped 

 body (Figure 11.13). 



CLASS EQUISETAE 



Diagnosis: the only recognized class; represented 

 by macrofossils since Lower, or perhaps Upper, 

 Devonian; characteristics as outlined for the sub- 

 phylum. 



OROPHYTE 



Figure 11.13 Life cycle of Equisetum, a horsetail. (Used by permis- 

 sion, from Arthur Cronquist, Introductory Botany, Harper, New York, 

 1961.) 



ORDER EQUISETALES (Horseiails and Scouring Rushes) 



Diagnosis: known from Upper Permian to Recent; 

 characters as emphasized in the subphylum account. 



Subphylum PTEROPSIDA (Ferns, Cycads, 

 Ginkgos, Conifers, and Angiosperms) 



Diagnosis: definite fossils from Devonian to Re- 

 cent; commonly perennial herbs or trees, also annu- 

 als; leaves usually pinnately compound or decom- 

 pound, rarely simple, always megaphylls; leaves 

 typically alternate, often radiating from the apex of 

 an aerial stem, and frequently large and conspicuous; 

 stem short and underground to aerial, unbranched 

 to branched; sporangia borne upon leaves or modified 

 leaves; spores of one or two kinds; gametophytes 

 small to minute, often distinctly male or female, with 

 or without distinct sex organs; with or without seeds; 

 an extremely variable group. 



Occurrence: over 200,000 living species of world- 

 wide occurrence and in almost every conceivable hab- 

 itat for a plant. 



