176 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



SOCIETIES AND CLANS. 



The desert scrub possesses an extraordinary wealth of herbaceous species. 

 The great majority of these are annuals, owing to the existence of two rainy 

 seasons separated by periods of drought. There are in consequence two 

 clear-cut growing seasons which may be regarded for the present as aspects, 

 though closer study may show that these are themselves divisible into aspects. 

 The two seasons are winter-spring and summer. Since they depend wholly 

 upon the incidence of the corresponding rains, the dates of beginning and 

 closing are extremely variable. After the severe drought of 1917, the first 

 winter annuals did not appear until March and the seasonal communities 

 were exceptionally dwarf, sparse, and short-lived. The continuance of the 

 drought brought about an almost complete failure of the summer annuals and 

 many of the herbaceous perennials. The occurrence of unusual rains in the 

 following autumn led to the first appearance of the most important annuals 

 by the beginning of December, and the ensuing development was exception- 

 ally complete and vigorous. 



Perennials: 



Allionia incarnata. 

 Aster spinosus. 

 Bahia absinthifolia. 

 Baileya multiradiata. 

 Boerhaavia viscosa oligadena. 

 Delphinium scaposum. 

 Euphorbia albomarginata. 

 Euphorbia capitellata. 

 Franseria tenuifolia. 

 Gutierrezia microcephala. 

 Hoffmannseggia drepano- 



carpa. 

 Hoffmannseggia jamesii. 

 Hoffmannseggia stricta. 

 Pappophorum wrightii. 

 Pentstemon wrightii. 

 Philibertella hartwegii heteio- 



phylla. 

 Rumex hymenosepalus. 

 Setaria composita. 

 Sida lepidota sagittifolia. 

 Solanum elaeagnifolium. 

 Sphaeralcea euspidata. 

 Teucrium cubense. 

 Triodia mutica. 

 Triodia pulchella. 

 Verbena ciliata. 



Long-lived Annuals: 

 Atriplex bracteosa. 

 Atriplex elegans. 

 Atriplex texana. 

 Chenopodium fremontii. 

 Eriogonum abertianum. 

 Eriogonum deflexum. 

 Eriogonum trichopodum. 



Long-lived Annuals — continued. 

 Euphorbia preslii. 

 Helianthus annuus. 

 Helianthus petiolaris. 

 Heterotheca subaxillaris. 

 Lepidium thurberi. 

 Machaeranthera parvifolia. 

 Machaeranthera tanacetifolia 

 Verbesina encelioides. 

 Wislizenia refraeta. 



Summer Annuals: 



Amarantus palmeri. 

 Aristida americana. 

 Bouteloua aristidoides. 

 Bouteloua polystachya. 

 Chloris elegans. 

 Cladothrix lanuginosa. 

 Eragrostis neo-mexicana. 

 Eragrostis pilosa. 

 Eriochloa punctata. 

 Kallstroemia brachystylis. 

 Kallstroemia grandiflora. 

 Leptochloa viscida. 

 Panicum hirticaulum. 

 Pectis papposa. 

 Pectis prostrata. 

 Physalis angulata linkiana. 

 Trianthema portulacastrum. 



Winter Annuals 



Actinolepis lanosa. 

 Amsinckia intermedia. 

 Amsinckia tessellata. 

 Astragalus nuttallianus. 

 Baeria gracilis. 

 Bowlesia lobata. 



Winter Annuals — continued. 

 Chaenactis stevioides. 

 Cryptanthe angustifolia. 

 Cryptanthe pterocarya. 

 Daucus pusillus. 

 Eremiastrum bellidioidea. 

 Eschscholtzia mexicana. 

 Evax caulescens. 

 Festuca octoflora. 

 Gilia nlifolia. 

 Harpagonella palmeri. 

 Lappula redowskii. 

 Lepidium lasiocarpum. 

 Leaquerella gordoni. 

 Lotus humistratus. 

 Lupinus leptophyllus. 

 Malacothrix glabrata. 

 Malacothrix sonchoides. 

 Malvastrum exile. 

 Mentzelia albicaulis. 

 Microseris linearifolia. 

 Monolepis nuttalliana. 

 Orthocarpus purpurascens. 

 Pectocarya linearis. 

 Pectocarya penicillata. 

 Phacelia crenulata. 

 Phacelia distans. 

 Phalaris caroliniana. 

 Plagiobothrys arizonicus. 

 Plantago fastigiata. 

 Plantago ignota. 

 Polypogon monspeliensis. 

 Salvia columbariae. 

 Sophia incisa. 

 Sophia pinnata. 

 Streptanthus arizonicus. 

 Thelypodium lasiophyllum. 

 Veronica peregrina. 



The more important herbs of the scrub are grouped in the following list 

 under four heads, viz, perennials, long-lived annuals, summer annuals, and 

 winter annuals. The first alone constitute true societies, the annuals repre- 

 senting the initial stage of a subsere which advances no further because of the 



