Vascular Plants of Williamson County by Arthur C. Gibson

Posted here are descriptions, as they are completed, of the vascular plants that can be found growing in wildlands and disturbed habitats of Williamson County, Texas. The descriptions have been researched from living materials, and therefore should match very closely what users will encounter within the county.


This is a project by Dr. Arthur C. Gibson, a botanist who retired to Georgetown from UCLA in mid-2012. He uses the process of describing plants, with considerable focus on precision, to learn what plants are growing here and things about their biology, and this website is a way to share those discoveries. For him, learning about local plants is an ongoing process, started in early January, 2013, and therefore nobody can predict either how quickly the descriptions will be posted or how many and in what order species will be studied and ready for public viewing.

Although readers probably expect that this will become a flora of Williamson County, that is not the goal. Professionally written regional and state floras are already available for central Texas. The Williamson County project, as currently defined, is to provide only descriptions, of high quality, comparable with plant descriptions in well-researched floras and generic monographs. A superb example for similar quality is the three-volume treatment by George Yatskievych (1999, 2006, 2013), Steyermark’s Flora of Missouri.

For Williamson County, and unlike most published floras, the website was not planned to include the following essential elements of a professional flora: history of collections and biographies of important collectors; discussions or classifications of habitats, soils, topography, and geology; distribution maps, taxon ranges, or documentation of specimens; illustrations of plants; dichotomous keys for identification; flowering times; taxonomic synonymy or points of taxonomic and nomenclatural confusion; conservation status; geographic origin and status in range (native versus introduced or waif); or economic and former human uses of plants and plant parts or uses by and dangers to livestock. Hence, Dr. Gibson’s Williamson County project should not be called a flora. Discussions are underway to determine whether original colored images can accompany the descriptions, to aid in identification.

Using fresh materials

A deliberate attempt is being made to write technical descriptions from living materials collected within Williamson County, regardless of what form the plant species may assume in other counties or states. Most users of this type of description will be trying to identify specimens in habitat or from freshly collected, local plant parts. This approach of using only living material is not practiced, or practical, for larger floras, wherein most materials are dried herbarium materials, often collected decades earlier.

To finish a complete description of all visible plant parts, observations are required over the course of the growing season. Often fresh collections must be collected over several months to include all vegetative, floral, fruit, and seed features. For example, ripe fruits of certain species may mature three or more months after flowers have faded. Care is given to include features of the plant that are often omitted in descriptions, such as bract-bearing parts of an inflorescence and structures of seeds and fruits only ascertained with high quality magnification. The researcher has not included anatomical details for which a compound microscope is required.

A description from living material should provide a complete, and hopefully nearly perfect, explanation of what fresh plant the user has in hand, so if the identification is correct, the description should fit like a glove, and if it does not, the user should question the identification. This requires the former professor to do his task properly, and to submit updated and improved descriptions, if posted ones are not good enough, for correcting any errors. The Internet, rather than a printed book, is the easiest, fastest, and most efficient way to make descriptions available to the public at the lowest cost, and to catalog without space limitations the characteristics of plants, potentially all plants on Planet Earth.

Materials used for descriptions are those encountered in areas where the plants are available to the public, because private lands are that…private…and respected as such for the project at hand. Consequently, plants taller or shorter, with larger or smaller, more or fewer parts, as well as variants in color, certainly occur within the county and will be missed.

Coverage for Williamson County and currently known species

Vascular plants are included for the county if 1) they have been collected, observed, or officially listed at least once by a competent researcher, and 2) occur within two kilometers outside the county boundary. These two working guidelines permit living materials to be used that, if not discovered yet, at some future date will likely be found on private or public lands within Williamson County.

Herbarium and other museum plant collections have not yet been tallied for the plant species of Williamson County. The TEX-LL collection at The University of Texas currently has specimens of 488 taxa, and many more specimens that have not yet been processed from the county. In volume one of Illustrated Flora of East Texas (Diggs et al., 2006) distribution maps indicate at least 30 more taxa occur in Williamson County, mostly graminoid monocotyledons, and the Botanical Research Institute of Texas also has an undisclosed number of documented dicotyledons for Williamson County. An additional 30 taxa are vouchered from Williamson County in the herbarium of the Balcones Canyonland National Wildlife Refuge.

Parks within Williamson County have been partially surveyed by professional botanists, who have generated several lists of species.

Known species of the local flora

Travis County has a rich and well-researched flora of its vascular plants, and the number of species and intraspecific taxa recorded in the county now approaches 1600. For full details, consult the thoroughly researched list of vascular plants known in Travis County prepared by Bill Carr.

The reasons are many why the plant species of Travis County are well known, but are due first to intense interest in plant research radiating from The University of Texas at Austin, which is one of the premiere centers of plant research in North America. Now the university is nested within an expanded Austin community keenly interested in native plants and natural areas. The flora of this county is a mixture of native species in a fairly diverse set of ecologic associations, introduced species of cultivated fields, pasturelands, and roadsides, weeds of the urban setting, and plant escapes and waifs of horticultural and agricultural plants.

In contrast, Williamson County, its neighbor to the north, is very poorly known, botanically speaking. Nobody can know with certainty how many what we call “native or naturalized” species will be found within the county, i.e., plants growing and reproducing without direct human intervention. One measure of this could be how many collections made by botanists and stored at the UT Herbarium (TEX) are from Williamson County versus the surrounding six counties. As of May 1, 2014, the TEX-LL database had the following specimen totals:

Given that Williamson County (2940 square kilometers) is the largest of the seven counties, with 10% more area than Travis County (2647 square kilometers), the difference in the two counties is certainly that there has been great botanical interest in Travis County and botanical neglect in the others. Milam County, having exactly the same area as Travis County, is also poorly botanized. Differences also are to be related to levels of terrestrial ecologic diversity, amount and nature of wetland habitat, and urbanization of this set of Texas counties.

Any effort to do an inventory of species within any county, and here for Williamson County, assists governmental agencies, land managers, conservationists, and growth planners what to expect and, hopefully, what needs to be preserved. Without a baseline, Williamson County has been working with the Native Plant Society of Williamson County to develop inventories for public lands at existing and future park sites. At the same time, some efforts are being made to produce herbarium collections of plants within the county, so that eventually at least one specimen can be cited for each species known in range. This will avoid the awkward situation now, wherein an official distribution map for a species is missing a dot in Williamson County, while botanists know it is there because distribution dots are present in adjacent counties. Until park inventories are completed and voucher specimens recorded, nobody can have a defensible guess on the number of plant species in Williamson County, although the current list is approaching 900 taxa for the county.

In the meanwhile, descriptions posted here are bookmarks that those species are present in the county. Every description is stand-alone, so that the user does not have to flip back and forth from species description to genus and family, as must happen using typical published floras. An attempt is made to describe flowers for groups that are often ignored in standard floristic treatments, so here the user eventually will be able to interpret flowers of “nonshowy” plants, such as grasses and oaks, using adequate magnification. There has been an attempt to reduce professional jargon and limit terms used to those in the included glossary, so that structures will be described in understandable two-dimensional or three-dimensional terms, such as sausage-shaped or bell-shaped or top-shaped rather than the poorer known botanical terms. Colors are described from a large palette rather than simple standards of red, yellow, green, purple, brown, etc. Each species is merely a very detailed account, without including general folklore, flowering dates in county, economic uses, toxic character, name etymology, and local occurrence and ecologic information, all fascinating but which are available in other Texas resources. The goal is, simply, to be focused on what the plant looks, feels, and smells like, and it will take probably eight to ten years of intense research just to finish that part of the project. This is not intended to be a definitive taxonomic work or textbook, and certainly is a supplement to, not a substitute for, existing major works on Texas plants.

Scientific nomenclature

Scientific names and vernacular names are, of course, THE bones of contention among users, whether names should remain relatively stable and standardized or permitted to change, and if changed to what. As a student of plant names, now for almost five decades, and one who published on thousands of species and also had to change some names legally, obviously a professional botanist like Dr. Gibson has opinions about the correct or appropriate name for a plant, but also lots of ignorance about most plant names. That he has a preference is obvious in his choice for each description of Williamson County. By and large, names used in the descriptions are those currently adopted by the TEX-LL database, but there are, and will be, differences with family, genus, and species names, and infraspecific trinomials. Names used by Gibson are chosen because they are considered to be the best current expression of plant genealogy, so that plants are classified with what they are mostly closely related in time−ancestor plus all genetic descendents−not what they most closely resemble. A tree of life. The world of plant nomenclature has been in a volatile state of change for two decades with the advent of DNA information, and scientific names will remain somewhat unstable until the molecular dust finally settles. This website gives clues as to where in the future names probably will be consistently adopted, but nobody has a monopoly on the truth in this field, nor a crystal ball what will be the final version of family names. Consensus is not something scientists are comfortable with, although the user public wants consensus for stability, but eventually the evidence will indicate which are the best designations of plant families and genera.

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