FLOWERING PLAXTS AND FERNS OF ARIZONA 585 



stamens 8, the filaments thickened at the middle; ovary 2-celled, 

 stipitate; fruit a globular berry with 2 to 4 seed-. 



Sometimes called "crown-of -thorns," " crucifixion-thorn ," and 

 "corona-de-Cristo." This very strongly armed plant repels livestock 

 and no doubt assists in controlling soil erosion. Wherever abundant 

 it is considered a range pest. It tends to form thickets. 



1. Koeberlinia spinosa Zucc, Flora 15 2 : Beibl. 73. 1832. 



Cochise County to the vicinity of Tucson (Pima County), 2,400 

 to 4.500 feet, hillsides and mesas. May and June. Western Texas to 

 southeastern Arizona and northern Mexico. 



The distribution in Arizona, as given in the preceding paragraph, 

 is that of the typical form. The var. U nuispina Kearney and Peebles 

 occurs farther west, in western Maricopa and southern Yuma Counties. 

 also in northwestern Sonora. Normally it differs from the typical 

 form in having longer and more slender branches, blaish-green rather 

 than yellowish-green bark, longer and relatively narrower sepals, 

 and longer petals and filaments. It flowers in March, hence earlier 

 than the typical form, prefers sandier soil, and grows at lower eleva- 

 tions, 2.000 feet or lower. The plant is usually more open and taller, 

 reaching a height of 4.5 m. (15 feet), whereas the typical form seldom 

 exceeds 1.8 m. (6 feet) in height. Further study may show this 

 variant to be a distinct species, but there is considerable variation 

 and some overlapping with typical K. spinosa in most of the characters. 



82. VIOLACEAE. Violet family 



Plants herbaceous, annual or perennial: leaves simple, with stipules, 

 alternate or all basal; flowers 5-merous, irregular, the lower petal 

 concave, saccate, or spurred; filaments very short or none; fruit a 3- 

 valved capsule. 



Two favorite garden plants, the pansy (Viola tricolor L.), and the 

 sweet violet (V. odorata L.) belong to this family. Both are natives 

 of the Old World. Many North American species of Viola have 

 beautiful flowers. 



Key to the genera 



1. Sepals not auriculate at base; lower petal concave or slightly saccate at base, 

 constricted at the middle; plants caulescent, the stems leafy; flowers axil- 

 lary, solitary or in small clusters 1. Htbanthus. 



1. Sepals dilated or auriculate at base; lower petal produced at base into a spur 

 or deep sac, not noticeably constricted at the middle; plants caulescent or 

 acaulescent; flowers solitary, on long, 2-bracted peduncles 2. Viola. 



1. HYBANTHUS 



Plants annual or perennial; stems leafy; leaf blades linear to rhom- 

 bic-lanceolate; flowers axillary, solitary or few in a cluster, incon- 

 spicuous, greenish or purplish. 



Key to the species 



1. Plant perennial; stems numerous from a slightly woody caudex, decumbent, 

 ascending, or erect, not more (usually much less N , than 35 cm. Ions; herbage 

 dull green, puberulent or glabrous; leaves sessile or subsessile, linear, lan- 

 ceolate, or oblanceolate the lowest ones sometimes obovate), QOt more 

 than 6 mm. wide, usually entire, acute or acutish at apex; flowers solitary; 

 pedicels commonly decurved; corolla 3 to 4 mm. long, the longest petal 

 much less than twice as long as the others, with a cucullate blade. 



1. H. VERTK ILLATUS. 



