313] 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. 



6;oa. T. marginatus tetramerus Cockerell. BOULDER SNOW- 

 ON-THE-MOUNTAIN. 



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 

 inornata 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. robnstus (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. philorus 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. 



