standley: new genus of allioniaceae 631 



each flower subtended by one or rarely 2 bracts, while in the 

 other species the few flowers are solitary or geminate in the leaf 

 axils, each subtended by 2 or 3 bracts. 



In 1913 Dr. Anton Heimerl, an eminent Austrian botanist 

 well known for his studies of this family of plants, pointed out 5 

 these differences and used them as a basis for the division of 

 Selinocarpus into two sections, Breviflori and Tubiflori. To the 

 writer, however, it seems that the section Breviflori deserves 

 generic rank, and the name Ammocodon is accordingly proposed 

 for it. The primary characters upon which the genus is based 

 are those of the flower and androecium, and they are certainly 

 of greater significance than the quantitative fruit characters 

 which are used to separate Selinocarpus and Boerhaavia. 



Ammocodon Standley, gen. nov. 



Erect or decumbent perennial herbs with thick roots and dichot- 

 omous pubescent stems. Leaves opposite, petiolate, those of a pair 

 often unequal, the blades succulent. Flowers umbellulate, the um- 

 bellules in open cymes, each flower subtended by a minute subulate 

 bract, or a second smaller bract rarely also present; perianth campanu- 

 late, purplish red, constricted above the ovary, shallowly 5-lobed, the 

 lobes plicate. Stamens 2 or rarely 3; filaments filiform, short-connate 

 at the base, free from the perianth. Ovary narrowly oblong; style 

 filiform, exserted; stigma peltate, smooth. Fruit a compressed antho- 

 carp, broadly 5-winged vertically, the wings hyaline. Testa of the 

 seed adherent to the pericarp; embryo conduplicate, the cotyledons 

 enclosing the farinaceous endosperm; radicle elongate, descending. 



Type species, Selinocarpus chenopodioides Gray. 



Ammocodon chenopodioides (Gray) Standley. 



Selinocarpus chenopodioides Gray, Amer. Journ. Sci. II. 15: 262. 

 1853. 



The type was collected by Charles Wright in valleys from Providence 

 Creek to the Rio Grande, western Texas. The species ranges from 

 western Texas through southern New Mexico to southeastern Arizona, 

 and southward into Chihuahua. It is very abundant in the region 

 about El Paso, growing chiefly in the loose sandy soil of the mesas, 

 usually along with creosote bush (Covillea glutinosa). The flowers are 

 not very showy, but bright-colored and borne in great profusion. Like 

 those of most, if not all, of the herbaceous members of the family, 

 they open late in the evening and close about noon or earlier the fol- 

 lowing day. 



5 Oesterr. Bot. Zeitschr., 63: 354-355. 



