ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

56 INTRODUCTION/SOIL-RELATED GEOLOGY, PINEYWOODS, POST OAK SAVANNAH
(Sellards et al. 1932; Brown et al. 1969). The average width of the outcrop of the Weches is
two to five miles (3.2 to 8 km) (Sellards et al. 1932). Surface exposures usually occur on slopes
(due to erosion) and are typically small, ranging from only 5 to 20 m wide and usually not
more than 100 m in length (George & Nixon 1990). Where freshly exposed, the glauconitic
strata have an olive green cast, but upon weathering become reddish brown (Fig. 27) (George
& Nixon 1990). Soils of the Weches Formation range from shallow and rocky (which apparently
limits voody vegetation) on the steeper slopes to deep on the flatter slopes (generally less than
5 to 8 percent), are characterized by a basic pH, and have a layer of glauconitic clay. They are
typically Alfisols with a distinctive red clayey subsoil. Outcrops of the Weches are often
waterlogged during the spring because of the clay stratum, since “downwardly percolating
water reaching the impermeable clay layer moves laterally until it exits on hillsides where the
outcrops occur” (George 1988). However, due to their shallowness, Weches outcrop soils can
become quite dry in summer and fall (George & Nixon 1990). The basic pH (7.1–8.2) is in
striking contrast to that of the mostly acidic soils of East Texas (pH 4.4–6.2) and is probably
of major importance in determining the unusual plant community occupying the outcrops.
The unique conditions provided by the Weches Formation result in the development
of “Glauconite shale glades” (Bezanson 2000), also known as Weches outcrop communities
(Fig. 28). These are usually small, isolated, natural opening or glade communities typically
having sparse woody growth and an unusual herbaceous assemblage, including two
endemics: Texas golden glade cress (Leavenworthia aurea var. texana) (Mahler 1987; Poole
et al. 2002) and the federally endangered white bladderpod (Lesquerella pallida) (George &
Nixon 1990). Interest in this habitat increased dramatically when Lesquerella pallida, now
recognized as endemic to Weches outcrops, was rediscovered in 1981 after having not been
seen since its initial collection in the 1830s (Nixon et al. 1983; George & Nixon 1990).
This species is currently known from only seven localities, all in San Augustine County
(Texas Parks and Wildlife 1999). A number of other species (e.g., Liatris mucronata,
Paronychia virginica, Petalostemum pulcherrimum) found on Weches outcrops are disjunct from
much further west in Texas. Similarities exist between the Weches outcrop communities and
those of the “cedar glades” well known in the southeastern U.S. and adjacent areas (see e.g.,
Baskin & Baskin 1985, 2000; George & Nixon 1990). Another interesting phenomenon is
the occurrence of the somewhat calciphilic Thaspium barbinode (Apiaceae), whose only
known Texas location is in Houston County on sand over the Weches. The nearest other
locations of this species are in the Ouachita Mountains of McCurtain County, Oklahoma,
and in deep ravines west of the Ouachita River in Caldwell Parish, Louisiana—disjunctions
of approximately 300 km (186 miles) (Bridges & Orzell 1989a).
The Weches can also significantly affect local topography (and thus vegetation). For
example, where erosion-resistant ironstone layers occur they cap hills and escarpments—
maximum local elevations are found in Anderson and Cherokee counties (Fogg & Kreitler
1982). The result can be “a picturesque, rugged topography of steep, high, flat-topped hills
dissected by deep V-shaped valleys” (Sellards et al. 1932). In areas without ironstone, the
topography can merely be rolling. Outcrops of the Weches are sometimes mined for road
material, gravel, or the fertilizer/soil additive greensand (though it is of low quality for this
use), while others are overgrazed or destroyed by various types of development. Unfortunately,
the unusual plant community on the Weches currently has virtually no protection in Texas.
QUEEN CITY FORMATION—The Eocene Queen City Formation represents delta deposits and
marginal marine sand shoals (Kreitler et al. 1980) and “consists mostly of thick bedded to
massive cross-bedded very fine to fine quartz sand that is interbedded with silt and clay.
Stringers of lignite and clay are present in the upper portions of the formation and layers of
shale are found deeper in the formation” (C. Miller Drilling 2001). Where porous sands of