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William R. Carr
Botanist, The Nature Conservancy of Texas
Research Affiliate, Plant Resources Center,
     The University of Texas at Austin

Some Plants of the South Texas Sand Sheet

Natural Regions of Texas South Texas Regions
[Adapted from Texas Parks and Wildlife Maps]

Ecological Setting

The South Texas Sand Sheet, also known as the Coastal Sand Plains and the Llano Mesteño, occupies more than two million acres at the southern tip of the state, just north of the Lower Rio Grande Valley. The region is defined by a sheet of eolian sand blown inland from the shoreline of the Gulf of Mexico during Holocene times, a sheet that covers most of Kenedy and Brooks counties as well as the northern tips of Willacy, Hidalgo and Starr counties. Although most maps place the western edge of the sand sheet in Jim Hogg County, isolated patches of Holocene sand are mapped within a few miles of the Rio Grande in northwestern Zapata County (Brewton et al., 1976) and are included for the purposes of this discussion. The eastern edge is somewhat arbitrary. Laguna Madre separates the Sand Sheet from modern barrier islands along the Gulf of Mexico, but there is no clear boundary between the Sand Sheet and the Flour Bluff Peninsula, a Pleistocene barrier island situated west of Laguna Madre in southern Nueces County.

Topography in the region is generally flat. Most parts of the sand sheet are a base-level plain with very little relief. Other parts, particularly those closer to the coast, are covered in active or stabilized dunes oriented along a northwest-southeast axis. Relief is greatest in Kenedy County, where some dunes west of Laguna Madre are as much as 50 feet tall. Elevation in the region ranges from near sea level in the east to about 800 feet near Hebbronville in the west. Drainage systems are limited, and the few wet-weather streams that arise in the western highlands typically terminate in miscellaneous lowlands rather than in Laguna Madre or the Gulf of Mexico. In flatter parts of the landscape, rainwater simply collects in and evaporates from small roundish potholes or copitas; in active dune fields, elongate swales are more common. Most of these wetlands are seasonal or intermittent, but a few are permanent. Most contain fresh water, but those lying along established drainageways lowest on the landscape tend to be saline. Lomas or clay dunes have developed on the downwind (northwest) side of larger ephemeral saline ponds.

Sand Sheet over Goliad Formation

Dune Field
Soils of the region are generally sandy. Characteristic soils of dune fields are light-colored, deep to very deep, well drained to excessively drained, neutral to slightly acid fine sand Alfisols and Psamments. Soils of planar areas are typically light brown, deep, moderately well drained to well drained, slightly acid fine sand Alfisols. In some areas, particular where the wind-blown sand is a thin veneer over calcareous sandstone and caliche of the Goliad Formation, typical soils are reddish-brown, well drained, neutral fine sandy loam Alfisols (Sanders et al., 1974; Thompson, 1972; Williamson, 1993). Soils of lomas are mapped as very deep, friable, dark grayish brown, calcareous, moderately alkaline fine sandy loam Mollisols.

Climate in the area is considered to be humid subtropical, with hot summers and mild winters. Mean annual precipitation ranges from 20 inches in Zapata County to 30 inches in Kenedy County. The average growing season ranges from 304 days in Zapata County to 319 days in Kenedy County (Natural Fibers Information Center, 1987).

Most of the South Texas Sand Sheet is dedicated to the production of cattle and huntable wildlife. Even in the 21st Century it is a region of very large ranches and very few people. The King Ranch, for example, occupies 825,000 acres, mostly in Kenedy County, and the estimated population of Kenedy County in 2003 was 408 persons (Dallas Morning News, 2004).

Where's the beef?


Seacoast bluestem
(Schizachyrium scoparium var. littorale)
Several matrix-level vegetation types can be recognized within the South Texas Sand Sheet. One type is a live oak (Quercus sp.) woodland that covers much of the dune topography in eastern Kenedy County and extends patchily westward. The nominative oak is said to be Quercus fusiformis. Other components of these woodlands include toothache-tree (Zanthoxylum hirsutum), honey mesquite (Prosopis glandulosa) and brasil (Condalia hookeri). Associated with this woodland is a tallgrass grassland dominated by seacoast bluestem (Schizachyrium scoparium var. littorale) and gulfdune paspalum (Paspalum monostachyum), with camphor daisy (Heterotheca subaxillaris) and other forbs more common on sand ridges (Diamond & Fulbright, 1990). Other important components of the grassland include brownseed paspalum (Paspalum plicatulum), crinkleawn (Trachypogon secundus), Indiangrass (Sorghastum nutans) and big bluestem (Andropogon gerardii) (Diamond & Fulbright, 1990).

Another major vegetation type in the region is honey mesquite woodland, which is found on light brown fine sands and reddish-brown sandy loams of plains. In such situations, mesquite typically occurs with colima or lime prickly ash (Zanthoxylum fagara), brasil, prickly pear (Opuntia spp.) and other thorny shrubs. Associated with this woodland is a midgrass grassland composed of lovegrasses (Eragrostis spp.), three-awns (Aristida spp.), fringed signalgrass (Urochloa ciliatissima) and other species. The balance between the grassland and woodland components may have been influenced by historic cattle grazing.

Mesquite, prickly pear savanna.

Arrowhead (Sagittaria longiloba)
Wetlands are common, although most are small and ephemeral. Deeper freshwater ponds and swales in the eastern part of the region have a well developed florula, with spikesedges (Eleocharis cellulosa, E. palustris and E. quadrangulata) often dominant. Other conspicuous components include arrowhead (Sagittaria longiloba), elegant waterlily (Nymphaea elegans), yellow-eyed grass (Xyris jupicai) and jointed flatsedge (Cyperus articulatus). Shallower freshwater ponds in the western part of the region, or ponds that are actively grazed, usually have shorter vegetation consisting of short sedge species (Eleocharis parvula, E. minimus and Schoenoplectus saximontanus) and burheads (Echinodorus berteroi and E. tenellus). Salt or brackish ponds typically have extensive open water rimmed by saline clay supporting sparse cover of a few halophytes, notably shoregrass (Monanthochloe littoralis) and white spikesedge (Eleocharis albida).

Also low on the landscape, mostly along drainageways near the coast, are bands of saline soils that support a variety vegetation types. One type is a short-stature shrubland typified by Drummond goldenweed (Isocoma drummondii), amargosa (Castela erecta ssp. texana), gutta percha (Maytenus phyllanthoides), dwarf screwbean (Prosopis reptans), rubberstem (Jatropha dioica), horse-crippler cactus (Echinocactus texensis), pricklypear and stunted honey mesquite. Associated grasses include alkali sacaton, (Sporobolus airoides) and whorled dropseed (Sporobolus pyramidatus). Also present are grasslands dominated by gulf cordgrass (Spartina spartinae).

Other localized vegetation types are medium-stature shrublands that occur on slopes of the region's few major drainageways, often where the underlying calcareous sandstone of the Goliad Formation is exposed, and on lomas upwind from salt lakes. These communities include many shrub species that are more commonly found in Tamaulipan thornscrub to the south and west. Patterns in these shrublands have not yet been discerned.

Depressional wetland

Endemic Plant Species

The flora of the South Texas Sand Sheet includes about 54 taxa that are endemic to the state of Texas (Table 1). Among those, fourteen are essentially endemic to the Sand Sheet proper. Photos of many of these species are provided on a separate page.

Table 1. Texas endemics known from the South Texas Sand Sheet. Asterisks indicate those taxa that are essentially endemic to the South Texas Sand Sheet
Family Scientific Name Common Name
Aizoaceae *Sesuvium trianthemoides

roughseed sea-purslane
Amaranthaceae Froelichia latifolia

broadleaf snake-cotton
Asclepiadaceae Matelea parviflora smallflower milkvine
Asclepiadaceae Matelea brevicoronata

shortcrown milkvine
Asteraceae Chaetopappa imberbis

bristle-free leastdaisy
Asteraceae Coreopsis nuecensis crown coreopsis
Asteraceae Coreopsis nuecensoides false crown coreopsis
Asteraceae Helianthus praecox var. runyonii Runyon's sunflower
Asteraceae *Hymenopappus artemisiifolius Rio Grande woollywhite
Asteraceae Liatris carizzana Carrizo blazing-star
Asteraceae Palafoxia hookeriana Hooker's palafoxia
Asteraceae Senecio ampullaceus Texas groundsel
Asteraceae Tetragonotheca repanda showy nerve-ray, sand box-flower
Asteraceae Tetraneuris linearifolia Sand Sheet bitterweed
Asteraceae *Thelesperma nuecense Coastal Bend greenthread
Asteraceae *Thymophylla tephroleuca ashy dogweed
Boraginaceae Cryptantha texana Texas hiddenflower
Brassicaceae Lesquerella grandiflora bigflower bladderpod
Capparaceae Polanisia erosa ssp. breviglandulosa South Texas clammyweed
Caryophyllaceae *Paronychia jonesii Jones' nailwort
Caryophyllaceae *Paronychia lundellorum Lundells' nailwort
Cistaceae Lechea san-sabeana San Saba pinweed
Commelinaceae Tradescantia humilis

Texas spiderwort
Commelinaceae Tradescantia subacaulis

stemless spiderwort
Euphorbiaceae *Croton coryi Cory's croton
Euphorbiaceae Croton parksii Parks' croton
Euphorbiaceae Ditaxis pilosissima pilose wild-mercury
Euphorbiaceae *Euphorbia innocua velvet spurge
Euphorbiaceae *Phyllanthus abnormis South Texas leaf-flower
Fabaceae Dalea austrotexana dune dalea
Fabaceae Dalea obovata stinking prairie-clover
Fabaceae Galactia canescens hoary milkpea
Fabaceae Galactia heterophylla varileaf milkpea
Fabaceae Lupinus subcarnosus sandyland bluebonnet
Fabaceae Tephrosia lindheimeri Lindheimer's tephrosia
Fumariaceae Corydalis micrantha Texas corydalis
Hydrophyllaceae Phacelia patuliflora South Texas phacelia
Lamiaceae *Brazoria arenaria

sand brazoria
Lamiaceae *Monarda fruticulosa bushy horsemint
Liliaceae Allium elmendorfii Elmendorf's onion
Liliaceae *Allium runyonii Runyon's onion
Malvaceae Sphaeralcea lindheimeri Lindheimer's globemallow
Nyctaginaceae *Abronia ameliae Amelia's sand-verbena
Onagraceae Oenothera falfurriae

Falfurrias evening-primrose
Onagraceae Oenothera mexicana

hairy cutleaf evening-primrose
Poaceae Dichanthelium nodatum Sarita panicum
Poaceae Digitaria texana(D. runyonii) Texas crabgrass
Poaceae Setaria firmula (Panicum firmulum) knotgrass
Poaceae Sporobolus tharpii

Padre Island dropseed
Poaceae Vaseyochloa multinervosa Texasgrass
Polygonaceae Polygonum striatulum

Kleberg knotweed
Rosaceae Prunus texana Texas peachbush
Rubiaceae *Houstonia correllii Correll's bluet
Rubiaceae Houstonia croftiae Croft's bluet
Rubiaceae Houstonia subviscosa sand-belt bluet
Solanaceae *Physalis mollis var. variovestita South Texas ground-cherry


Many people graciously provided access to the properties on which most of the photographs on these pages were taken. Special thanks are owed to Monica and Ray Burdette, El Canelo Ranch; Steve and Toddy Burns, Encinitos Ranch; Dr. Lester Dyke, Long Rifle Ranch; Guerrero family, Las Comitas; Mrs. Luella Hauser, Charco Salado Ranch; Hunke family, El Tecolote Ranch; Kipp Layton, Eshleman-Vogt Ranch; Paul and Patti Pauley, San Rodolfo Ranch; Bud Payne, Payne Ranch; Betta Thomas, Thomas Ranch; Armando Vela, Vela ranches; and Lisa Williams and Sonia Najera of The Nature Conservancy.

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