1.  To collect, identify, and preserve specimens of all vascular plants occuring in a county
2.  To generate a species list for the county and delineate patterns of plant communities by habitat preference
3.  To analyze the flora for notable range extensions, recent invaders, and endemic or rare taxa

County floras play an important role in preserving information about the species composition of a known area at a particular time.  The true geographic range of many species in the United States is unknown.  The distribution of species changes as environments change, and if no one is appointed to focus their attention on these changes, we will have an incomplete understanding of the natural world as it affects us and is affected by us.  Not only must the members of endangered plant communities be recorded before they are disturbed or obliterated, but botanists are responsible for alerting the public to the movement of invasive non-native species.  Unfortunately, the county flora is a labor-intensive and time-consuming project, and many counties in Texas (and other states) lack a concentrated floristic study.  I encourage students of botany to find such a county nearby, and dedicate yourselves to this under-publicized method of becoming a better botanist while producing an important record of your research.

The geology of this part of eastern Texas is the product of alluvium washed southward by rivers and deposited in layers by the advancing and retreating coastal waters during the Eocene Epoch (58-37 mya) of the Tertiary Period.  The Eocene layers deposited in Madison County are members of the Claiborne Group and are composed of clays, claystones, shales, siltstones, sandstones, and lignite.  Along the larger creeks and rivers, Pleistocene (2 mya-10,000 ya) fluvial terraces of distantly-derived sands, clays, and gravel were deposited during high-moisture periods of the last ice age.  Recent, more locally-derived Holocene (10,000 ya-present) alluvium covers modern floodplains in the county.   (See soils map below)

In the map above, the pink, orange, medium blue, and purple soils are terraces deposited by the rivers bordering the county.  The green soils are alluvium deposited by the smaller tributaries.  The light blue, dark blue-grey, yellow, and tan soils are older soils directly derived from the underlying geology of the county.  Generally, these are clays and sandy clays.

Map from Neitsch, C.L. 1994. Soil survey of Madison County, Texas. U.S.D.A., Soil Conservation Service, Wash., D.C.

The above map represents historical vegetation patterns in Madison County, which supports three of the ten vegetation types found in the state of Texas.  The Blackland Prairies are true prairies with fertile calcareous soil and dominant grasses such as Little Bluestem and Indian Grass.  Tree species found along waterways include a variety of oaks, hickories, and elms.  No intact, undisturbed prairies are preserved in Madison County, but patches of prairie-like habitats exist along some roadsides and in other areas protected from overgrazing.  The Post Oak Savannah is a zone of deciduous hardwoods, namely Post Oak, Blackjack Oak, and Winged Elm, interspersed with open grassy areas.  Common understory shrubs are Yaupon Holly and American Beautyberry.  The majority of upland Post Oak Savannah in Madison County had been cleared in the past for farming, but the county has become more heavily wooded in the last 50 years.  The Pineywoods of east Texas represent the highest rainfall area in the state, and are characterized by forests of Loblolly Pine, Sweetgum, oaks, and hickories.  Farkleberry and Sassafras are common understory species.

Map adapted from Gould, F.W., G.O. Hoffman, and C.A. Rechenthin. 1960. Vegetational areas of Texas. Texas Agric. Exp. Sta. Bulletin 1070.

Ten species in the flora are endemic (restricted)to Texas.  Liatris cymosa (Branched Gayfeather) is restricted to approximately six counties in southeast Texas.  Although its restricted range places it in danger of extinction, this species is not under review for federal listing.  Spiranthes parksii (Navasota Ladies'-tresses Orchid) was listed as federally rare and endangered in 1982, and is restricted to approximately eight counties in southeast Texas. 

148 non-Texas-native taxa were found in the county, or almost 14% of the total taxa in Madison County.  The majority of these are roadside and pasture weeds, favored by disturbance and occasionally introduced for forage.  There are some crop waifs that are found along roadsides, as well as horticultural introductions persisting at old home sites.  A number of species were found in the county that are either well-known invaders, or new arrivals (marked with *) that appear to be future threats.  A selection of these is given below.  Grass species are the worst invaders and displacers of native species, but are usually introduced purposefully.  These are too many to list, but the worst offenders are Bermuda Grass (Cynodon dactylon) and species of Paspalum.
 

Links to great sites focusing on invaders: Center for Aquatic and Invasive Plants
                                                                      Weeds Gone Wild
                                                                      The Nature Conservancy Wildland Invasive Species Program

Vascular plants were collected in Madison County from 1996-2000, resulting in a total of 2,254 specimens.  The flora totals 1,071 taxa (including subspecies and varieties) in 994 species, with 469 genera and 121 families.  One species, Vicia lutea (Yellow Vetch), was found to be new to Texas.

The five largest plant families in the flora are Poaceae (grasses) (134 species), Asteraceae (composites) (130 sp.), Fabaceae (beans in the strict sense) (74 sp.), Cyperaceae (sedges) (63 sp.), and Euphorbiaceae (spurges) (32 sp.).  These families comprise approximately 44% of the species found in Madison County.

Partial funding for this project was supplied by the Department of Biology and the Office of Graduate Studies at Texas A&M University.  Many thanks to the landowners and leaseholders of Madison County for your participation in this research!

The interested reader is referred to the author's thesis, which is available in both the Sterling C. Evans Library on the A&M campus and the Madisonville Public Library.

Questions should be addressed to the author, Amanda K. Neill, at aneill@brit.org

resurrected 1-31-07, 8-18-2011