3I3] FLORA OF BOULDER, COLORADO 165 



270. TITHYMALUS Adans. 



670. T. marginatus (Pursh) Cockerell [Euphorbia margi- 

 nata Pursh; Dichrophyllum marginatum (Pursh) Kl. & 

 Garcke]. Snow-on-the-mountain. 



Plains and mesas about Boulder, 5100-6000 ft. (Daniels, 

 188). My specimens have flowers with five glands. 



Minnesota to Montana; Missouri to Texas and Colo- 

 rado. 



670a. T. marginatus tetramerus Cockerell. Boulder snow- 



ON-THE-MOUNTAIX. 



Very common about Boulder; although in some plants the 

 central flower of each umbel has five petaloid appendages, 

 the others have but three or four. An occasional form — forma 

 iuornata has the white margin of the leaves obsolete, or 

 nearly so, but my material is too scant to enable me to deter- 

 mine whether this is characteristic of the variety alone, though 

 a few of my specimens have the central flower with five 

 appendages, 5100-7000 ft. (Daniels, 957). 



671. T. robustus (Engelm.) Small [Euphorbia montana ro- 

 busta Engelm.]. Stout spurge. 



High mesas fronting the Flat-irons, 5700-6000 ft. (Daniels, 

 187). Also at Longmont (Rydberg). 

 South Dakota to Montana ; Colorado to Arizona. 



672. T. philoras Cockerell [Euphorbia montana Engelm.; not 

 Raf.]. Mountain spurge. 



Frequent on the plains, mesas and foothills, 5500-8000 ft. 

 (Daniels, 16). Boulder Canon (Porter & Coulter). A 

 form, — forma dichotoma (Daniels, 367) from the high ridges 

 of Green Mt. repeatedly forks into long leafy branches topped 

 by a cluster of two or three flowers, with a few others in the 

 axils of the upper leaves, the central cyme or umbel not being 

 present. 



Colorado to Utah ; Texas to Arizona. 



673. T. Arkansanus (Engelm. & Gray) Kl. & Garcke [Eu- 

 phorbia Arkansana Engelm. & Gray]. Arkansas spurge. 



