The Texas Gulf coast is almost continuously fringed by barrier islands and peninsulas, creating many miles of beaches. The barrier islands are long and narrow and run parallel to the coast. Some of them are true islands; others are connected to the mainland at one end, and are more properly but infrequently called spits. Exceptions are Bolivar Peninsula, near the Louisiana border, and Matagorda Peninsula. Although this book will be useful throughout the Texas coast, the "islands" and beaches specifically dealt with are Bolivar Peninsula, Galveston Island, Matagorda Island, Goose Island, Mustang Island, Padre Island, Brazos Island, and Boca Chica Beach. Of the islands mentioned, Matagorda Island is the widest. Padre Island is the longest barrier island in the world (Britton & Morton 1989).
The local name of Boca Chica Beach includes all the beach area from the Brazos Santiago Pass (now the Brownsville Ship Channel) to the Rio Grande. I have chosen to use the established name of Brazos Island for the northern section (Brazos Santiago Pass to the Boca Chica inlet), and to limit the term "Boca Chica Beach" to the southern section, which extends from Brazos Island to the Rio Grande. Highway 4 makes a convenient dividing line between the two beaches, since it is only a few hundred feet south of the Boca Chica channel.
Most visitors to the beaches, and even many residents, see only the sands between the surf and the first low dunes. Since only a few plants grow in this small section, it is easy to get the impression that these areas consist mostly of barren sand. In fact, the opposite is true. Beyond that first low dune there is an amazing variety and abundance of native plant species. Many of them, like the Indian Blanket, Goldenrod, and Seaside Gerardia, produce great splashes of color. Others produce more modest flowers, or are interesting for their growth habits. Over seven hundred species of flowering plants have been found growing on Texas beaches and islands.
The dunes run parallel with the Gulf shore. Sometimes there are two groups of dunes, resembling a miniature mountain chain, with a valley in between them. Some of the dunes have been known to reach almost forty feet in height (Britton & Morton 1989). The "valley" is higher than the beach area and the salt flats, which are located behind the dunes. Behind the second group of dunes, the terrain gradually slopes down toward the bay, which separates the island from the mainland. This downward slope is interrupted by a number of low, rounded dunes.
There are contrasting areas in which there are no dunes at all. Here the terrain is almost flat from Gulf shore to bay shore. These broad areas may be natural relief zones for the flow of water into and out of the bay during strong storms.
There are various intermediate conditions between the two described extremes. For example, there may be one set of dunes instead of two, or there may be scattered low dunes. A strong hurricane can level many or all of the dunes. Then a gradual rebuilding of the dunes begins.
Generally, the dunes and dune systems contain almost pure sand, and the lower elevations contain varying amounts of clay mixed with the sand. Because of the proximity to the Gulf of Mexico and its bays, there is usually a high saline content. The broadest islands would tend to have some soils with lower salinity and also with more clay and organic content. Also, the grains of sand tend to become larger as one progresses from north to south (Britton & Morton 1989).
The differences in elevation, soil types, and moisture are some of the factors creating many habitats where an amazing number of plant species thrive (Sullivan & Richardson, in manuscript). I have observed that sometimes an elevation change of even one or two inches seems to favor the growth of one species over another. From Aransas Pass northward there is more rainfall (Britton & Morton 1989), and so some plants that grow in the northern portions do not survive farther south.
The intent of this book is to illustrate samples of the flamboyant and more commonly seen, the more modest, and even some of the very tiny but very interesting flowers of the native plants that can be found on our beaches and islands. Plants of the sandy soils are emphasized, but many plants of the heavier soils are also included. About 38 percent of the species reported for the islands are illustrated. It is my hope that, through use of the illustrations and descriptions, the reader will come to appreciate and learn more about the natural flora of this rich area.
Distribution of the plant is noted in each species description. Information on distribution was derived from personal surveys as well as published checklists, which are listed in the bibliography. Since most surveys were done during a single season, there would naturally be some omissions. Therefore, a plant may be listed as growing on just one island, but it could, in fact, be more widespread. In fact, many of the plants illustrated here probably occur throughout our beaches. Many are also found growing on the mainland along or near the bays.
In a technical book, plants would be arranged according to relationships by family, genus, and species. The species is the basic unit. Related species are placed in a group called a genus. Related genera are placed in a group called a family. In this book, the plant families are arranged according to relationships and similarities. Within each family, the genera are arranged in alphabetical order, and within each genus the species are also in alphabetical order.
Common names were derived from the Manual of the Vascular Plants of Texas (Correll & Johnston 1970), Flora of the Texas Coastal Bend (Jones 1975), Guide to Grasses of the Lower Rio Grande Valley, Texas (Lonard 1993), Plants of the Rio Grande Delta (Richardson 1995), and the checklists of Padre Island (Lonard et al. 1978, Negrete et al. 1999), Mustang Island (Gillespie 1976), Matagorda Island (Hartman & Smith 1973), Galveston Island State Park, Goose Island State Recreation Area, and Mustang Island State Park (Texas Parks and Wildlife, unpublished).
Recently, several authors have attempted to bring the taxonomy of Texas plants up to date (that is, to establish the single correct name for each plant). One recent book (1997) is Vascular Plants of Texas, by Stanley Jones et al. Unfortunately, the authors do not always agree. The natural result is a certain amount of confusion. This book follows The Vascular Plants of Texas: A List, Up-dating the Manual of the Vascular Plants of Texas, second edition, by Marshall C. Johnston.
Those who want to learn more about the plants may refer to several floristic studies (Gillespie 1976; Hartman & Smith 1973; Jones 1975; Lonard, Judd & Sides 1978; Lonard & Judd 1980; Negrete et al. 1999; Richardson 1995). Aransas: A Naturalist's Guide and Matagorda Island: A Naturalist's Guide, both by McAlister and McAlister, contain much useful information. The Manual of the Vascular Plants of Texas, by Correll and Johnston (1970), describes all the species of plants known to grow in Texas at the time of publication. Britton and Morton's Shore Ecology of the Gulf of Mexico (1989) provides useful detail regarding the topography, soils, etc.