24 MISC. PUBLICATION 4 2 3, U. S. DEPT. OF AGRICULTURE 



ANNOTATED LIST OF THE PLANTS OF ARIZONA, WITH KEYS 



Key to the -phyla 



Plants without flowers, producing spores, not seeds Pteridophyta. 



Plants with flowers, producing seeds Spermatophyta. 



PTERIDOPHYTA. Ferns and fern allies 



Contributed by William R. Maxon 



Plants exhibiting a life cycle of two well-marked phases, sporophyte 

 and gametophyte. The former, known commonly as a fern or fern 

 ally, is differentiated into root, stem, and leaf, is provided with vascular 

 tissues, and bears spores asexually, these either alike or of two kinds 

 called megaspores and microspores. On germinating, the spore 

 produces the gametophyte or minute sexual stage (pro thallium). 

 The large growth phase developing from the impregnation of an egg 

 cell of the prothallium by a single coiled motile male element 

 (spermatozoid) is the sporophyte. 



Key to the families 



1. Leaves very numerous, spirally arranged in many ranks upon freely branched 

 creeping stems, minute, lance-subulate or bractlike, sessile, never united; 

 plants heterosporous, producing megaspores and microspores. 



7. Selaginellaceae. 



1. Leaves fewer, mostly much larger, or, if small, united in short sheaths upon 



the stem or its branches; plants either homosporous or heterosporous (2). 



2. Stems jointed, fluted, mostly hollow, simple and rushlike or with numerous 



whorled branches; leaves minute, united in toothed sheaths at the nodes; 



sporophylls small, borne in terminal cones 6. Equisetaceae. 



2. Stems not jointed or fluted, solid, without whorled branches; leaves mostly 

 large, simple to compound; sporophylls never in cones (3). 

 3. Plants terrestrial, homosporous (4). 



4. Sporangia very large, sessile, united in a simple fleshy apical spike or 

 borne in a loose terminal panicle, the sterile blade (simple to com- 

 pound) appearing lateral 1. Ophioglossaceae. 



4. Sporangia minute, mostly long-stalked, borne in clusters (sori) on the 



back of ordinary leaves 2. Polypodiaceae. 



3. Plants aquatic or of wet situations, producing both megaspores and micro- 

 spores (5). 



5. Leaves grasslike, tufted upon a very short trunk, the sporangia borne 



within their expanded hollow bases 5. Isoetaceae. 



5. Leaves not grasslike; sporangia not borne within hollow leaf bases (6). 

 6. Plants rooting in mud; sori 4 to many, borne within large free, bony, 



septate, basal conceptacles 3. Marsileaceae. 



6. Plants floating, minute; sori indusiate, borne in pairs on the sub- 

 mersed lower lobe of the leaves 4. Azollaceae. 



1. OPHIOGLOSSACEAE. Adderstongue family 



Sporophytes herbaceous, with short fleshy rhizome and long fleshy 

 roots; leaves (fronds) 1 or several, consisting of a simple, pinnatifid, 

 or dissected sterile blade and (if fertile) a stalked sporebearing spike 

 or panicle, borne at the apex of a common stalk; sporangia marginal, 

 in 2 rows, sessile, opening by a transverse slit; spores uniform; 

 gametophytes (prothallia) hypogean, tuberlike. 



Key to the genera 



1. Sterile blade simple, with reticulate veins; sporangia united in a simple slender 

 fleshy spike 1. Ophioglossum. 



1. Sterile blade 1 to 4 times pinnately divided, witn free veins; sporangia globose, 

 distinct, borne in a panicle _ _ I 2. Botrychium. 



