December 2012 Number 1 - Utah Native Plant Society

Utah Native Plant Society
¡Viva thamnophila! Ecology of Zapata Bladderpod
(Physaria thamnophila), an Endangered Plant of the
Texas-Mexico Borderlands
Dana M. Price,
US Army Corps of Engineers, Albuquerque District
Christopher F. Best,
US Fish and Wildlife Service, Austin Ecological Services Field Office
Norma L. Fowler,
Section of Integrative Biology, University of Texas at Austin,
and Alice L. Hempel,
Department of Biology and Health Sciences, Texas A&M University- Kingsville
Abstract. Conserving rare plants is dependent upon our ability to identify, manage and restore their habitat. We examined
the plant community associates and habitat requirements of Physaria thamnophila, an endangered herbaceous
perennial of the Tamaulipan shrubland of south Texas, at four sites from 2003 to 2007. At each site, vegetation
height structure and species composition were sampled concurrently with intermittent censuses of P. thamnophila.
We found significant and interesting differences among sites and years, as well as between our quantitative results
and previous descriptions of P. thamnophila’s community and habitat. Existing plant community descriptions and
mapped soil types do not provide a close match with our field observations. Finally, we discuss the application of
these results to conservation of P. thamnophila and restoration of its community.
An endangered plant that is a member of a fragmented
and altered remnant plant community poses
many challenges to conservation workers. In addition to
threats to its (usually) few and small known populations,
two additional challenges are faced. One, the detection
of additional populations is often hampered by uncertainty
in identifying its habitat; and two, uncertainty
about its habitat requirements hampers management and
restoration efforts. Physaria thamnophila (Zapata bladderpod;
Brassicaceae) is one such plant. This endangered
herbaceous perennial of south Texas grows in
remnants of Tamaulipan thornscrub, likely on a specific
but as yet poorly defined soil type and geologic substrate.
Prior to the present study, the structure and composition
of the specific plant community in which Zapata
bladderpod occurs had been examined quantitatively
for only one site (Sternberg 2005).
The U.S. Fish and Wildlife Service (USFWS) Recovery
Plan (USFWS 2004) highlights the need for better
knowledge of the habitat and community in which P.
thamnophila lives for several purposes, including discovering
additional populations, locating sites for establishing
new populations, and restoring and managing its
habitat. This study addresses these goals by providing a
detailed, quantitative description of the habitat and
community of four sites with persistent (as defined by
NatureServe 2002) P. thamnophila populations. The
results will not only be useful for P. thamnophila conservation,
but can improve our ability to manage and
restore one of the communities that comprise the
Tamaulipan thornscrub ecosystem.
SPECIES
Physaria thamnophila (Rollins and E.A. Shaw)
O’Kane and Al-Shehbaz (formerly Lesquerella thamnophila)
is a federally listed endangered species (USFWS
2004) with a global conservation ranking of G1
(critically imperiled; NatureServe 2009). It is a shortlived
perennial with a rosette of silvery- or gray-green
leaves covered with stellate trichomes (Figure 1) and
one to several flexuous, sprawling to ascending flowering
stems. The yellow flowers give rise to subglobose
silicles on recurved pedicels (Rollins and Shaw 1973)
(Figure 2). It usually flowers in spring (February to
April), but can flower during midsummer or as late as
September in response to rain (Poole et al. 2007; Sternberg
2005). Germination has not been observed, but
probably occurs in response to rainfall in cool weather.
Under prolonged dry conditions, all of the plant’s leaves
may die, making some surviving plants very difficult to
locate.
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