KEY TO THE FAMILIES AND ABERRANT GENERA 



la. Plants without flowers or seeds, reproducing by means of spores.. . I. PTERIDOPHYTA 

 lb. Plants with flowers that produce seeds II. SPERMATOPHYTA 



I. PTERIDOPHYTA 



la. Sporangia borne in strobili, axils of lvs., sporocarps, or on spike- 

 like branches. 

 2a. Plants aquatic. 



Floating on water: lvs. small: sporocarps borne on under-side 



of stem 6. Salviniaceae, p. 46 



Rooting in mud of ponds or ditches (may be dry for a part of 

 the year). 

 Lvs. quadrifoliolate: rhizome widely creeping: sporocarps 



borne near base of leaf stalk 5. Marsileaceae , p. 46 



Lvs. elongate, grass-like, in rosettes: stem corm-like: 



sporangia borne in base of the lvs 4. Isoetaceae, p. 45 



2b. Plants terrestrial . 



3a. Sporangia borne in strobili or in axils of lvs. 



Stems jointed, hollow: only a whorl of scale-like lvs. at the 



nodes: strobili terminal ; rush-like plants 1. Equisetaceae 



Stems not jointed, creeping or erect: lvs. very small, closely 

 imbricated. 



Spores of one type : lvs. uniform 2. Lycopodiaceae 



Spores of two sizes: median and lateral lvs. usually 



dimorphic 3. Selaginellaceae 



3b. Sporangia borne on a simple or pinnately branched fertile seg- 

 ment: sterile blade simple or compound 7. Ophioglossaceae 



lb. Sporangia borne on the back or margins of foliage lvs. or on 

 specialized leaves which usually lack chlorophyll. 

 4a. Plants aquatic, submersed and rooting in mud or floating: sori 



marginal, covered by reflexed leaf margin 12. Ceratopteridaceae 



(Parkeriaceae) 

 4b. Plants terrestrial. 

 5a. Rachis indeterminate, long and twining; pinnae palmately or 



pinnately lobed; fertile 1ft. segments contracted 9. Schizaeaceae 



5b. Rachises determinate, not twining. 



6a. Fertile lvs. conspicuously unlike the sterile. 



Fertile lvs. or fertile portion of lvs. bipinnate; sporangia 

 borne in irregular compound clusters (not on the back 



of leaf blades); dehiscence by a vertical slit 8. Osmundaceae 



Fertile lvs. pinnate; sporangia borne on the back of con- 

 tracted pinnae; dehiscence by a transverse slit. 

 Rhizome and stipe without scales: sterile If. pinnate: 



fertile pinnae with very narrow indusia 13. Plagiogyriaceae 



Rhizome and stipe scaly: sterile If. pinnate to bipinnati- 

 fid: fertile pinnae with broad coriaceous reflexed 



margins 14. Onocleaceae 



(Matteuccia) 

 6b. Fertile lvs. and sterile lvs. essentially alike. 



7a. Leaf-blades thin: sori marginal: indusia tubular or bilabiate. 11. Hymenophyllaceae 



5 



