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A3170 Pleuraphis rigida Desert Grassland Alliance

Type Concept Sentence: This Mojave and Sonoran desert grassland and shrub-steppe alliance is dominated by the semi-woody perennial grass Pleuraphis rigida often with low cover of Ambrosia dumosa or Larrea tridentata and typically occurs on sandy substrates found on flat ridges, lower slopes, stabilized sand dunes and sandsheets, and sandy plains.

Common (Translated Scientific) Name: Big Galleta Desert Grassland Alliance

Colloquial Name: Big Galleta Desert Grassland

Hierarchy Level:  Alliance

Type Concept: This Mojave and Sonoran desert grassland and shrub-steppe alliance is dominated by the semi-woody perennial grass Pleuraphis rigida. Other associates in the herbaceous layer include Achnatherum hymenoides, Bouteloua eriopoda, Dalea mollissima, Gutierrezia sarothrae, Panicum urvilleanum, and Sphaeralcea ambigua. Scattered shrubs such as Ambrosia dumosa, Larrea tridentata, Yucca brevifolia, or other desert shrubs may be present with lower cover than Pleuraphis rigida. Stands occur on sandy substrates found on flat ridges, lower slopes, stabilized sand dunes and sandsheets, and sandy plains.

Diagnostic Characteristics: Pleuraphis rigida 10-35% absolute cover in the herbaceous layer; emergent shrubs or trees <10% absolute cover (Keeler-Wolf et al. 1998). The shrubby grass Pleuraphis rigida is the dominant perennial species and can be considered in the same layer as commonly occurring shrubs such as Larrea tridentata, Ambrosia dumosa, Ephedra trifurca, or other species. Stands are often mixed with lower cover of other shrubs and found on sand ramps, dune aprons, stabilized dunes near playas, or wide washes adjacent to Larrea tridentata-Ambrosia dumosa desert scrub stands. The westernmost occurrence of this type is west of Barstow near Hinkley, California (T. Keeler-Wolf pers. comm. 2014).

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Pleuraphis rigida is a native perennial grass with solid (rigid) stems that are highly branched at the base, giving it a shrubby appearance. The coarse, rigid culms are semi-woody and grow up to 1.5 m in height. It is a long-lived plant (>100 years) with a clumpy growth form as a result of the tillers or short rhizomes. Ecologically, this long-lived, tufted, bushy grass acts like a shrub, which helps it stabilize loose and blowing sand when it grows in desert dunes and sandsheets. The importance of Larrea tridentata diminishes as substrates become sandier and less stable. It is not an indicator of this alliance. This alliance combines two old alliances: Pleuraphis rigida Herbaceous Alliance (A.1246) and Pleuraphis rigida Shrub Herbaceous Alliance (A.1539).

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: This medium-tall, semi-arid, bunch grassland forms an open herbaceous layer usually less than 1 m in height often with scattered emergent shrubs. The perennial grass Pleuraphis rigida may act ecologically as a shrub with its tufted, above-ground branching, and non-rhizomatous habit. Ambrosia dumosa or Larrea tridentata may be dense enough to form an open shrub layer with Pleuraphis rigida occupying the same height strata (0.5-1.5 m).

Floristics: This desert grassland and shrub-steppe alliance is dominated by the semi-woody perennial grass Pleuraphis rigida in the herbaceous layer with Achnatherum hymenoides, Bouteloua eriopoda, Dalea mollissima, Gutierrezia sarothrae, Panicum urvilleanum, and Sphaeralcea ambigua also occurring. Scattered shrubs such as Larrea tridentata, Yucca brevifolia, Ambrosia dumosa, or Ephedra trifurca may be present with lower cover than Pleuraphis rigida. A number of other dune-adapted, perennial plants may occur. Occasionally Croton californicus, Croton wigginsii, Ephedra trifurca, Eriogonum deserticola, Petalonyx thurberi, Psorothamnus emoryi, or Psorothamnus schottii may be present to codominant. Total vegetation cover varies from 5-20% depending on slope aspect and dune activity. Diagnostic psammophytes include Abronia villosa var. villosa, Dicoria canescens, and the rare taxa Chamaesyce platysperma, Croton wigginsii, Eriogonum deserticola, Helianthus niveus ssp. tephrodes, Palafoxia arida var. gigantea, and Psorothamnus emoryi (Bowers 1984). Additional rare species that may be found include Pholisma sonorae (= Ammobroma sonorae), Stephanomeria schottii, and Triteleiopsis palmeri. This alliance contains a high number of ephemeral forbs; in the Gran Desierto dunes, ephemerals comprise up to 63.5% of the flora (Felger 1980). Ephemeral forbs include Dimorphocarpa pinnatifida, Dicoria canescens, Lupinus arizonicus, and Oenothera deltoides. Sandy stands adjacent to freeways and areas of disturbance often have a significant non-native component of Brassica tournefortii, Bromus rubens, Schismus spp., etc.

Dynamics:  No Data Available
Environmental Description:  This grassland and shrub-steppe alliance of the Mojave and Sonoran deserts occurs on sandy plains, sand ramps, dune aprons, stabilized desert sand dunes and sandsheets near playas, or wide washes adjacent to Larrea tridentata-Ambrosia dumosa stands (Sawyer et al. 2009). It occurs at elevations ranging from 75-1400 m (Sawyer et al. 2009). Yearly precipitation totals are between 0 and 25 cm. There is much year-to-year variation in precipitation. The summers are extremely hot. Winter temperatures, particularly at higher elevations, can get quite cold. Substrates include sand and loamy sand.
Geographic Range: Stands of this alliance occur at scattered sandy locations throughout the Mojave and northern Sonoran deserts.

Nations: MX,US

States/Provinces:  AZ, CA, MXSON, NV


Confidence Level: Moderate

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 3 Desert & Semi-Desert Class C03 3
Subclass 3.A Warm Desert & Semi-Desert Woodland, Scrub & Grassland Subclass S06 3.A
Formation 3.A.2 Warm Desert & Semi-Desert Scrub & Grassland Formation F015 3.A.2
Division 3.A.2.Na North American Warm Desert Scrub & Grassland Division D039 3.A.2.Na
Macrogroup 3.A.2.Na.4 Saguaro - Organ Pipe Cactus - Burrobush Mojave-Sonoran Semi-Desert Scrub Macrogroup M088 3.A.2.Na.4
Group 3.A.2.Na.4.e North American Warm Semi-Desert Dune & Sand Flats Group G675 3.A.2.Na.4.e
Alliance A3170 Big Galleta Desert Grassland Alliance A3170 3.A.2.Na.4.e
Association CEGL000955 Burrobush / Big Galleta Dwarf-shrubland CEGL000955 3.A.2.Na.4.e
Association CEGL003051 Big Galleta Grassland CEGL003051 3.A.2.Na.4.e
Concept Lineage: This alliance combines two old alliances Pleuraphis rigida Herbaceous Alliance (A.1246) and Pleuraphis rigida Shrub Herbaceous Alliance (A.1539).

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: = Pleuraphis rigida (Big galleta shrub-steppe) Alliance (Sawyer et al. 2009) [41.030.00]
= Pleuraphis rigida Herbaceous Alliance (Evens et al. 2014)
= Pleuraphis rigida Herbaceous Alliance (Evens et al. 2012)
>< Creosote Bush Scrub (Cheatham and Haller 1975)
? Galleta Grass Series (Paysen et al. 1980)
>< Mojave Creosote Bush Scrub (#34100) (Holland 1986b)
>< Mojave Mixed Steppe (#34220) (Holland 1986b)
>< Mojave Yucca Scrub and Steppe (#34230) (Holland 1986b)
>< Sonoran Creosote Bush Scrub (#33100) (Holland 1986b)
>< Valley Needlegrass Grassland (#42110) (Holland 1986b)
Concept Author(s): J.O. Sawyer, T. Keeler-Wolf, and J. Evens (2009)

Author of Description: K.A. Schulz

Acknowledgements: No Data Available

Version Date: 12-21-15
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