FLOWERING PLANTS AND FERNS OF ARIZONA 45 



Mountains (Pima County), 3,000 to 6,000 feet, dry cliffs and ledges. 

 Western Texas to Arizona and northern Mexico. 



5. Selaginella neomexicana Maxon, Smithsn. Misc. Collect. 72 5 :2. 

 1920. 

 Paradise, Cochise County, about 5,000 feet (J. H. Ferriss in 1904). 

 Westernmost Texas to southern Arizona. 



SPERMATOPHYTA. Flowering plants 



Seed-producing plants, the first phase of the life cycle very brief and 

 concealed. Pollen grains (microspores) borne in anther sacs (micro- 

 sporangia). Ovules (macrosporangia) enclosed in an ovary (except 

 in the Gymnospermae), each ovule containing an embryo sac (macro- 

 spore). Embryo resulting from the union of an egg cell in the embryo 

 sac and a pollen grain, the ovule thereupon developing into a seed 

 containing the embryo, the latter usually consisting of 1 or more leaves 

 (cotyledons), a hvpocotyl and radicle, and a terminal bud (plumule). 



KEY TO THE CLASSES AND SUBCLASSES 5 



1. Stigma none; ovules and seeds not enclosed, borne on the face of a scale or 



bract Class Gymnospermae. 



1. Stigma or stigmas present; ovules and seeds in a closed cavity (ovary). 



Class Angiospermae (2). 

 2. Cotyledon usually 1; flower parts commonly in 3's; stem not differentiated 

 into bark, wood, and pith (endogenous); veins of the leaves mostly longi- 

 tudinally parallel (sometimes with netted veinlets between the parallel 



principal veins) Subclass Monocotyledoneae. 



2. Cotyledons usually 2; flower parts commonly not in 3's; stem differentiated 

 into bark, wood, and pith (exogenous); veins of the leaves seldom 

 parallel (commonly branching at a greater or less angle from the mid- 

 vein, this alone extending the whole length of the leaf). 



Subclass Dicotyledoxeae (3). 

 3. Perianth none, or single or appearing so, with segments all much alike in 



texture and color Series 1 . Apetalae. 



3. Perianth present, evidently double, the outer segments (calyx) and the 

 inner segments (corolla) usually conspicuously different in texture 

 and color (4). 



4. Petals separate or united only at base Series 2. Polypetalae. 



4. Petals united well above the base Series 3. Gamopetalae. 



GYMNOSPERMAE 



Key to the families 



1. Stems not jointed; leaves narrowly linear or needlelike, or else scalolike, 

 crowded, and imbricate; fruits in woody cones, or berrylike 1. Pixaceae. 



1. Stems jointed; leaves reduced to scales, these distant, opposite, or in whorls 

 of 3; fruits in small thin-scaled cones 2. Gnetaceae. 



ANGIOSPERMAE-MONOCOTYLEDONEAE 



Key to the families 



1. Plants strictly aquatic, immersed in or floating on the surface of water; perianth 

 none or inconspicuous (2). 

 2. Flowers perfect, in spikes, 4-merous; leaves alternate, with or without 



broad floating blades: Genus Potamogcton 5. Naiadaceae. 



2. Flowers unisexual (3). 



3. Stems elongate; leaves narrowly linear or filiform, mostly opposite or 

 whorled; flowers axillary, solitary ( r in small umbellike clusters. 



5. Naiad \<k \k. 



5 In this key, as well as in the keys to the families, the genera in each family, ami the species in each 

 genus, the characterizations are restricted so as to apply only to forms that occur in Arizona. 



