72 POLYGONACEAE 



XXI. Salsuginosa. 

 One species. 122. E. salsuginosum. 



2. OXYTHECA Nutt. 



Stem-leaves and bracts lanceolate, connate only at the base; involucres pedicelled. 



1. O. foliosa. 

 Stem-leaves and bracts connate, forming a nearly circular disk; Involucres sessile. 



2. O. perfoliata. 



3. CENTROSTEGIA A. Gray. 1. C. Thurberi. 



4. CHORIZANTHE R. Br. 



Involucre not strongly sulcate, 5-tootlied ; filaments adnate to the perianth nearly up to 

 the base of the lobes. 1. C. Watsoni. 



Involucres strongly sulcate, 6-toothed; filaments adnate only to the lower part of the 

 perianth-tube. 

 Leaves Unear-oblanceolate to linear. 2. C. brevicornu. 



Lower leaves broadly spatulate. 3. C. spathulata. 



5. ACANTHOGONUM Torr. l. A. rigidum. 



6. PTEROSTEGIA F. & M. l. P. drymarioides , 



7. RUMEX L. Dock, Sorrel. 



Flowers dioecious; foliage acid. 



Leaves with auricled or hastate bases. 



Inner perianth-lobes not developed into wings in fruit; achenes granular. 



1. R. Acetosella. 

 Inner perianth-lobes developed into wings in fruit; achenes smooth. 



2. R. Acetosa. 

 Leaves narrowed at the base, neither auricled nor hastate. 3. R. paucifolius. 



Flowers perfect, or andro-polygamous; foliage not acid. 

 Inner perianth-lobes entire, undulate, or denticulate. 

 Inner perianth-lobes in fruit without tubercles. 



Inner perianth-lobes in fruit more than 2 cm. broad; plants perennial, with 



deep-seated woody rootstock. 4. R. venosus. 



Inner perianth-lobes in fruit less than 1.5 cm. in diameter. 



Plants perennial, with clusters of tuberous roots; inner perianth-lobes in 

 fruit 1-1.5 cm. broad. 

 Achene 7 mm. long or more ; inner perianth-lobes in fruit broader than 



long; plant low. 5. R. salinus. 



Achenes about 5 mm. long; inner perianth-lobes in fruit longer than 

 broad. 6. R. hymenosepalus. 



Plants with taproots or thickened rootstocks; inner perianth-lobes in 

 fruit 5—10 mm. broad. 

 Plants low, less than 3 dm. high, perennial, with short tuber-like root- 

 stock ; fruit maturing before the inner perianth-lobes become enlarged. 



7. R. praecoz. 

 Plants tall, perennial, with a taproot, not with a tuber-like root- 

 stock; inner perianth-lobes well enlarged in fruit. 



Basal leaves 2-3 cm. wide, acute or rarely rounded at the base. 



8. R. hesperius. 

 Basal leaves 5-20 cm. wide, rounded, cordate, or truncate at the 



base. 

 Inner perianth-lobes in fruit with rounded apex, not conspicu- 

 ously punctate. 

 Inner perianth-lobes in fruit 8-10 mm. wide. 



9. B. confinis. 

 Inner perianth-lobes in fruit 5-6 mm. wide. 



10. R. occidentalis. 

 Inner perianth-lobes abruptly pointed, conspicuously punctate. 

 Fruiting inner perianth-lobes about as broad as long, sinuate 



on the margin. 11. B. densiflorus. 



Fruiting inner perianth-lobes longer than broad, sharply 

 dentate. 12. R. subalpinus. 



Inner perianth-lobes or at least one of them bearing a tubercle in fruit; perermials 

 with a taproot. 

 Only one perianth-lobe tubercled. 



Leaves dark green, more or less crisp; fruiting inner perianth-lobes 8-9 



mm. broad, reniform. 13. R, Patientia. 



Leaves pale green, not crisp; fruiting inner perianth-lobes 5-6 mm. broad. 

 , „ ... deltoid-oyate. 14. r, altisHmus. 



All three penanth-lobes bearmg tubercles. 



Leaves dark green, crisp; fruiting perianth-lobes ovate to reniform, den- 



ticulate. 15. ij. crispus. 



Leaves pale green, not crisp; frmtmg perianth-lobes deltoid, entire. 



T • 4.1. 1 V, •_ * t • 1 i ...,. -. ^. 16. B. mexicanus. 



Inner penanth-lobes in fruit spmulose-toothed on the margin. 

 Tall plants; lower leaf-blades cordate at the base; one tubercle. 



17. R. obtusifolius. 



