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§ 3. Setispina: adscendentes: articuli plerumque minores: aculei 
pauci, teretes seu vix angulati, graciles, flexiles, pallidi: bacca 
minor. 
13. O. tenuispina, E. in B. C. R.: articulis majusculis obovatis 
basi attenuatis laete viridibus; pulvillis subapproximatis setas graciles 
breves fulvas gerentibus plerisque armatis ; aculeis 1-2 elongatis 
albidis cum 1-4 brevioribus inferioribus ; floris flavi ovario clavato ; 
petalis obovatis retusis ; bacca oblonga profunde umbilicata ; semini- 
bus minoribus. 
Sand-hills near El Paso : fl. May. — Joints 3-6 inches long, 2-4 
wide ; leaves very slender, hardly 2 lines long; upper spines sub¬ 
erect, or spreading, 1£ - inches long ; flower 2J - 3 inches in diam¬ 
eter ; seeds less than 2 lines in diameter, very irregular. — Similar 
in many respects to 0. phceacantha , which grows with it; but readily 
distinguished by the spines and fruit. 
14. O. setispina, E. in Salm, H. D.: articulis suborbiculatis par¬ 
vis glaucis ; pulvillis confertis setas flavidas gerentibus, omnibus arma¬ 
tis ; aculeis 1-3 longioribus subfngulatis et 3-7 brevioribus plus 
minus deflexis, omnibus gracillimis. 
Pine woods in the mountains west of Chihuahua, Dr. Wislizenus. 
Joints not over 2 inches long; pulvilli only 3-4 lines apart; longer 
spines 1 - lj- inches long, very slender, like bristles. Flower and 
fruit unknown. 
15. O. filipendula, E. in B. C. R.: glauca ; radicibus nodoso- 
incrassatis; articulis minoribus orbiculatis seu obovatis seu oblanee- 
olatis tenuibus ; pulvillis approximate setas virescenti-flavas graciles 
numerosas gerentibus armatis vel inermibus ; aculeis, si adsunt, 1-2 
elongatis subangulatis cum 1-2 minoribus, omnibus albidis; floris 
purpurascentis ovario gracili; stigmatibus 5; seminibus minoribus 
tumid is. 
' Alluvial bottoms of the Rio Grande near El Paso, and eastward on 
the Pecos : fl. May and June. — The long knotted roots, the small 
bluish joints, with the very small leaves and very long bristles, to¬ 
gether with the purple flower, and thick very narrowly margined 
seeds, distinguish this species from all others. Plant 6-12 inches 
high, joints 1J - 3 inches long, 1-2 wide ; pulvilli 4-6 lines apart; 
lower spines 1-2 inches long. Flower 2% inches in diameter. Seed 
hardly 2 lines in diameter. 
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