Tamaulipan Caliche Grassland

Geology

This system occurs on sites that have a relatively thin veneer of eolian sand over caliche substrate. Such sites occur on the edge of the South Texas Sand Sheet where it overlies caliche of the Goliad Formation.

Landform

These grasslands occur on relatively level sites atop the Goliad formation.

Soils

Shallow sands and sandy loams, sometimes red sandy loams, over caliche substrate.

Parent Description

This system is described from the vicinity of Loreto in Tamaulipas, Mexico, but the conditions of sand veneer over caliche outcrop may also be present on the edge of the sandsheet where it passes over the Goliad Formation in northern Hidalgo and Starr Counties. Soils are a reddish sandy loam about 0.3 m in depth or less. Such sites may currently be occupied by non-native grasses such as Pennisetum ciliare (buffelgrass) and Bothriochloa ischaemum var. songarica (King Ranch bluestem), though invasion by these species is not observed in Mexican occurrences (Chris Best, pers. obs.). These grasslands are known to occur within a mosaic of calcareous shrublands. Johnston (1963) describes them as grassland patches (the largest of which are 50 to 100 acres in extent) within a matrix of shrubland. Grasses often dominate sites, including species such as Schizachyrium littorale (seacoast bluestem), Aristida purpurea (purple threeawn), Bouteloua hirsuta (hairy grama), Elionurus tripsacoides (Pan American balsamscale), Trachypogon spicatus (crinkleawn), Heteropogon contortus (tanglehead), Bouteloua curtipendula (sideoats grama), Tridens texanus (Texas tridens), and Tridens muticus (slim tridens). Brachiaria ophryodes and Bouteloua radicosa (purple grama) are also noted from occurrences in Mexico. Shrubs and sub-shrubs are scattered and sometimes coalesce into larger areas, and include species such as Calliandra conferta (Rio Grande stickpea), Krameria ramosissima (calderona), Calliandra biflora (twoflower stickpea), Chamaecrista greggii (Gregg's senna), and Macrosiphonia lanuginosa (plateau rocktrumpet). Perennial forbs are conspicuous and include species such as Heliotropium confertifolium (leafy heliotrope), Melampodium cinereum (blackfoot daisy), Simsia calva (awnless bush sunflower), Acalypha radians (cardinal's feather), Cnidoscolus texanus (Texas bull-nettle), Galphimia angustifolia (narrowleaf thryallis), Hermannia texana (Mexican mallow), Croton capitatus (hog croton), Rhynchosia americana (American snoutbean), and Dalea nana (dwarf dalea). Scattered shrubs that may be present include Prosopis glandulosa (honey mesquite), Zanthoxylum fagara (colima), Cordia boissieri (anacahuita), and Condalia hookeri (brasil).