No^ 1.1 GEAY AND HOOKER ON THE ROCKY MOUNTAIN FLORA. 47 



juorplions and of immense geographical range. It is worth noting here 

 that the other genus, LittoreUa, till now su[)pose(l to be wholly European, 

 has been detected at three or four stations within and near the northern 

 borders of the United States. 



ISTyctaginace^.— Are essentially absent from the Atlantic flora, 

 abundant in the Texano-Arizonian 5 are represented by Oxybaphus on 

 the plains eafet of the Eocky Mountains and by Abronia beyond them ; 

 also by Quamoclidion or Mirabilis with several-flowered calciform invo- 

 lucre. The Great Basin has a peculiar genus, Hermidium of S. Wat- 

 son, allied to Bougainmllcea of South America, but herbaceous. 



Amarantace^ (weeds excluded). — Are chiefly of the Rocky Mount- 

 ain region in its warmer and drier i^arts. Acnida, however, is more 

 eastern. 



Chenopodiace^.^ — Are of similar distribution, but far more numer- 

 ous and diverse. They are the most characteristic and abundant of the 

 plants of the dry interior region, as has been elsewhere stated, and 

 they naturally extend into the Pacific flora more than into the Atlantic. 

 Atriplex is the great genus. Grayia and Sarcobatus are the endemic 

 shrubby genera. Spirostachys is of an extratropical South American 

 type. Cycloloma and Bucldeya are herbs peculiar to the eastern plains. 



Phytolaccace^. — Are represented only in the Atlantic flora, and 

 by a single Phytolacca, Rwina belonging farther south. 



Polygonace^. — The genuine Polygonece on the Atlantic and Pacific 

 sides by Polygonum and Bumex, and by Polygonella in the southern part 

 of the former ; and there are a few in the interior, where Rumex venosns 

 is a characteristic x)lant. But the most characteristic plants of the two 

 western floras, and the most numerous in species, if not in individuals, 

 .are the Eriogoneoi. The genus JEriogonum, founded at the beginning of 

 the century upon the single-known and still the only Atlantic species, 

 now comprises nearly 100 species in our western floras, and the subsid- 

 iary genera [OxytJieca, Gentrostegia, Ghorizanfhe, WemacauUs, Hollisieria^ 

 ^nd Lastarreia, all mainly Californian, and three of them also Chilian) 

 about three score more. Pferostegia, of California, proves to be most 

 related to the arctic-alpine Kcenigia. Another type is represented in 

 the southern part of the Atlantic flora by the jieculiar genus Brunnichia. 



PodostemaceyE. — Aquatic plants of tropical or subtropical rivers, 

 mostly of the southern hemisphere. A single Podostcmoji, on which 

 the genus and order were founded, belongs to the Atlantic United States. 

 Its congeners are all in Brazil, Madagascar, and India! 



ARTSTOLOCHiACEiE. — Abscut from the whole intermediate region, 

 there are three species of Asarum in the Atlantic and three others in 

 the Pacific flora ; three of AristolocMa'm the former and one in the latter. 



PiPERACE^, tribe Sanrurew. — A Sanrurus in the Atlantic flora, the 

 only other one Chino- Japanese ; a Houttuynia (if not a good genus, 

 Anemiopsis) in California and thence to Mexico; its relatives also East 

 African. 



