Compiling the Weed Lists

The CLW and PLANTS lists were both downloaded in 2020 when the review began. The lists were organized by scientific name and merged in order to compare the common names in 2020. Information for plant species represented in the PLANTS database that were not represented in the CLW were removed as part of process of merging the two lists.

Finding Discrepancies

A preliminary evaluation of the merged list of plant species was conducted to identify cases in which common names were the same in both databases and cases in which common names needed to be reviewed. The merged list of plant names comprised a total of 5,423 lines of data, not all of which represented unique species due to discrepancies between the databases that created duplicates when merged. The status was determined (as follows) during the preliminary evaluation:

1. 1. Common names were the same (1,078 cases).

2. 2. Common names were orthographically different (e.g., slight differences in spelling, hyphenation, spacing, capitalization, diacritical marks) (219 cases).

3. 3. Common names were completely different (1,744 cases).

4. 4. Common names were flagged as different because PLANTS gives “.” (no value) as common name (1,178 cases).

5. 5. Common names were flagged as different because PLANTS gave “NA” as common name (128 cases).

6. 6. Common names were flagged as different because CLW gave “see [species taxonomic synonym]” (1,076 cases).

No action was initially needed for statuses 1 and 6. These were initially omitted from the review, leaving 3,270 cases (statuses 2, 3, 4, and 5) that were reviewed by the committee. This preliminary evaluation did lead the committee to conclude that an initial objective of complete reconciliation of common names from the two sources would not be feasible due to the large number of cases of complete divergence.

Creating Guidelines for Decisions on Names

In March 2021, the committee began to develop guidelines for determining how names in the CLW could be written to be more consistent (punctuation, compound words, endings, capitalizations) and less discriminatory (e.g., derogatory slang, imperialist possessive language) and to change a name in the CLW to to match the PLANTS name. The committee initially agreed that reconciling the common names in CLW and PLANTS as much as possible would be a goal, but that in cases in which a plant was a very widespread, common, or troublesome weed, the CLW name should be conserved in the interest of facilitating communication about those plants as weeds. By September 2021, the following list of guidelines was agreed upon by the committee and WSSA board:

1. 1. Botanically incorrect or inappropriate names will be changed (i.e., spring whitlowgrass → spring whitlow, because it is not a grass)

2. 2. Punctuation will be removed with the following conditions:

   1. a. Hyphens will be removed, and the word will become compound or separate in accordance with similar words in PLANTS database.

   2. b. Possessive “’s” will be dropped entirely in case of proper nouns, following the example of Palmer amaranth (not Palmer’s amaranth; e.g., Nuttal X rather than Nuttal’s X).

   3. c. The apostrophe will be dropped and the “s” remain in cases of common nouns, following the example of “shepherds purse.”

3. 3.

   1. a. Words will not be separated when the compound word refers to a distinct group of plants:

      1. I. E.g., sowthistle, goldenrod, ragweed, honeysuckle, burdock, chickweed, milkweed, morningglory.

      2. II. Usually this is in agreement with PLANTS, but sometimes not, see rule 3c.

   2. b. Words will not be separated when the compound word is a commonly used combination of a descriptor and plant part:

      1. I. E.g., broadleaf, cutleaf, dayflower.

      2. II. Refer to the PLANTS database for other examples of the word in question to determine commonality.

   3. c. Words will not be separated when the PLANTS name contains a hyphen:

      1. I. E.g., PLANTS uses swallow-wort, star-thistle, but CLW uses swallowwort, starthistle. Words of this type should stay together as CLW already has them.

      2. II. In some cases, the opposite may be true. CLW name may contain two words and PLANTS has a hyphen. In this instance, the CLW name may stay separated.

4. 4. Complete name departures from the PLANTS list will be conserved as CLW (Palmer amaranth, yellow indigo) unless:

   1. a. The CLW name is inappropriate or culturally insensitive (Eastern Jew mallow). See rule 1.

   2. b. The CLW name is not specific to the specific epithet, for instance, when the WSSA common name refers to a group of plants or could apply to several species (many species are a type of “yellow rocket”; PLANTS differentiates between them, while WSSA refers only to Barbarea vulgaris as “yellow rocket”). In these cases, an adjective may be added.

   3. c. The name is not a very common weed in WSSA communication and literature and there is a very good justification for the plant to be referred to by the PLANTS name instead.

5. 5. Names that differ from PLANTS only in capitalization or word endings will be conform to PLANTS unless:

   1. a. Weed is common in WSSA communication and literature (i.e., johnsongrass, fall panicum).

Review

The list of 3,720 cases with status 2, 3, 4, or 5 were evenly split among four teams of two members within the committee (Figure 1). Each team carefully reviewed 100 to 200 cases per month and then brought any suggested changes or cases that required deliberation to the whole committee. After all cases of disagreement between the two databases were completed, the committee decided that there was a need to evaluate the cases that initially matched (status 1) but might be inconsistent with the new naming guidelines for the CLW that were developed during the review. After all common names were reviewed, suggested changes were compiled and again reviewed by each member of the committee who individually voted to approve or reject each change (Figure 1).

Figure 1. Illustration of committee review workflow. USDA, U.S. Department of Agriculture; WSSA, Weed Science Society of America.

Finalized List

Once all suggested changes were compiled and approved by a majority of committee members, the list of changes was sent to the WSSA board, who discussed and approved the changes on January 31, 2023. The final list can be found at https://wssa.net/weed/composite-list-of-weeds, although we do not expect this to be a permanent, definitive list. Some names that were debated and ultimately not changed may be changed in the future, while others that were not considered may be the subject of future discussion.

Conflicts between CLW and PLANTS Common Names

One clear result from this effort to reconcile common names is the extent of disparity between the names used by these two organizations, WSSA and USDA. At the onset of the review, a quick search of the most common and problematic weeds in the PLANTS database led to much discussion among the members due to the differences in common names of some species that are ubiquitous in weed science. For example, Amaranthus palmeri is listed as “carelessweed” in the PLANTS database instead of the well-cited “Palmer amaranth” in weed science literature. Review of the whole WSSA list revealed 2,254 names inconsistent with the PLANTS database (Figure 2). When reviewing such a large number of plants it was difficult for the committee to decide whether changing any particular common name would benefit our overall goal of facilitating communication.

Figure 2. Conflicts between the Weed Science Society of America Composite List of Weeds (WSSA CLW) and U.S. Department of Agriculture–Natural Resources Conservation Services Plant List of Attributes, Names, Taxonomy, and Symbols (USDA-NRCS PLANTS) common names in 2020 at the review initiation. Matches are in blue and conflicts in yellow. Solid colors represent names that have been included in a weed contest list in the past 15 years.

One important function of the CLW is in promoting a shared terminology when training future weed scientists and practitioners. Weed science courses, extension programming, and other training opportunities held throughout the United States have used and will continue to use the CLW as the reference for names of weedy plant species. Species lists included in weed identification events at weed contests held each summer represent a level of consensus within the regional weed science societies that certain species should be identifiable by trainees, and thus the committee considered this a good basis for the species of greatest concern. The committee compiled weed contest species lists that were available to establish name guidelines. After compiling lists from 14 weed contests held in the southern and northeastern regions or nationally between 2005 to 2019, 351 unique common names were found, but only 272 unique plants, most of which were still in conflict with the PLANTS names (Figure 2).

Inconsistencies in Names within the List

Inconsistencies in orthography (i.e., spelling, spacing, punctuation, and capitalization) between common names with similar lexical construction (i.e., linguistic meaning) were not standardized across the CLW. Some differences in common names between the PLANTS and CLW databases were often solely orthographical, but PLANTS had no better consistency in naming conventions. In the current digital landscape, orthography matters when conducting text searches. Many plant common names are compound words with many possible orthographical variants. For example, “mouse ear chick weed,” “mouseear chickweed,” and “mouse-ear chick-weed” could all be considered reasonable variants of the common name of Cerastium fontanum Baumg. ssp. vulgare (Hartm.) Greuter & Burdet. Even before Internet text searches, the first list published by the WSSA Terminology Committee noted: “Hyphenated and possessive names have largely been eliminated. Preference is given to unified or linked names such as eveningprimrose, morningglory, pepperweed, and canarygrass for groups of species with a basic common name” (WSA 1960, p. 496). Efforts of this review have more closely aligned with this sentiment in the current list revision.

Many plants are named after places and people, which are proper nouns that would be capitalized conventionally in English grammar. However, there are examples of names that share this origin and have lost their capitalization over time, like jimsonweed or johnsongrass, or refer to a common noun that could be mistaken for a proper noun, like turkey. This change was made consistent in the CLW published by WSSA in 1966: “Combined names involving a proper name such as bermudagrass, christmasberry, and joepyeweed are not capitalized. Proper names derived from persons or places are capitalized when used separately in the common names such as Kentucky bluegrass, Jim Hill mustard and Howell manzanita” (WSA 1966, p. 348). This was the first time that johnsongrass, formerly Johnsongrass, was listed in lowercase according to the combined name logic. It is possible that after the list was standardized according to this logic in 1966 that eventually other names were added without undergoing the change. In this review, we maintained that if the former proper noun was compounded, the name was not capitalized.

It was also discussed whether it is necessary to include qualifiers such as “common,” “grass,” and “weed.” In names of ubiquitous species such as common lambsquarters (Chenopodium album L.), use of “common” at first seems unneccessarily cumbersome, yet knowing that many other Chenopodium species besides C. album have common names that include “lambsquarters,” the committee felt it was necessary to keep “common” as a qualifier for many species (Table 1). In evaluating names with “grass” and “weed,” it was even clearer that such names must be kept until another name should present itself. For example, ragweed, pepperweed, Texas weed, and Mexican weed could not very well be shortened without an entirely new name. Therefore, it was decided that such plants should have a consistent placement throughout the list by using a space or a hyphen or being connected to the previous word in the compound.

Table 1. Table of common names in the Weed Science Society of America Composite List of Weeds (WSSA CLW) with the word “common” as a descriptor

^a Asterisks (*) denote species common names that were changed in the review.

Justification of Changes

For the entire set of common names in the CLW (2,847 unique species), it was decided that most species would retain their common names despite a conflict with the PLANTS database name (Figure 3). The committee ultimately recommended changes to common names of 371 species, with changes ranging from minor spelling corrections to complete adoption of the PLANTS name. Suggested changes were generally intended to accomplish one of three goals: (1) to remove inaccurate or insensitive names, (2) to simplify and standardize orthography, or (3) to match the PLANTS database name when doing so would not be expected to cause confusion or conflict in the weed science community. Specific reasons were cited for each suggested change and are summarized in Table 2. Of the 2,476 species without any suggested change, there were 207 species that had a taxonomic discrepancy that will need to be looked at more closely in the next review and were not considered for common name changes at this time. The list was reviewed and approved by seven of the eight committee members with one abstention.

Figure 3. Overview of suggested changes. Green and blue with polka dot pattern were not changed from the 2017 version of the CLW. P23, Weed Science Society of America (WSSA) P23 Committee on Standardized Plant Nomenclature; USDA, U.S. Department of Agriculture.

Table 2. Summary of changes to the Weed Science Society of America Composite List of Weeds (WSSA CLW) from 2017 to 2023 according to justification and comparison to the database by U.S. Department of Agriculture–Natural Resources Conservation Services Plant List of Attributes, Names, Taxonomy, and Symbols (USDA NRCS PLANTS)

The Stories behind Names

Common, standard, or scientific names of plants are rarely determined arbitrarily and most have a history, real or imagined, that assists in remembering the plant. Usually, the source of a naming conflict faced by scientists lies between differentiation and standardization. The rich variety and meaning of localized names can be lost in standardization. Some common names are related to the plant’s cultural role, use, or adverse effects, as is often the case with cultivated and weedy plants (e.g., any plant with “weed” in its common name). Many common names are descriptive in nature, referring to distinct morphological characteristics that aid in identification of the species (e.g., velvetleaf [Abutilon theophrasti Medik.] and shepherds purse [Capsella bursa-pastoris (L.) Medik.]). Others refer to a plant’s ecological role (e.g., butterfly milkweed [Asclepias tuberosa L.]), native geographic range (e.g., Eurasian watermilfoil [Myriophyllum spicatum L.]), place of cultural origin (e.g., jimsonweed [Datura stramonium L.]), or to important figures at the time the name was adopted (e.g., Palmer amaranth [Amaranthus palmeri S. Watson]). Common names reflect the sentiment of the communities that adopt them, but also shape and are shaped by the dialogue about the species they refer to as their usage spreads beyond the locations where the names originally arose.

Memorializations in plant names can be found in a vast number of species. These memorializations can occur from Greek mythology, farmers, or scientists. For example, Palmer amaranth was named after Edward Palmer (1829–1911), a British botanist and early American archaeologist in 1877 (Safford Reference Safford1911). He is known as the “Father of Ethnobotany” and gathered extensive natural history collections in North and South America during the late 19th century (Vasey and Rose Reference Vasey and Rose1890). More than 200 species are named after him. As another example, Colonel William Johnson, a farmer in Marion Junction, Alabama, established his namesake, johnsongrass [Sorghum halepense (L.) Pers.], along the Alabama River in the 1840s as a forage species (Ball Reference Ball1902). Johnsongrass was likely introduced to the United States before this time, but searching for documentation has been hampered due to the use of more than 40 common names and 8 scientific names for this weed during the 19th century (Snowden Reference Snowden1936). It is likely that broad use of the common name johnsongrass in the United States resulted from an 1874 letter from Herbert Post of Selma, Alabama, to USDA employee George Vasey (McWhorter Reference McWhorter1971). By 1896, the USDA deemed johnsongrass a “severe weed” and initiated research to control it in 1900 (Coville Reference Coville1896; Galloway Reference Galloway1901).

Memorializations in names have a long tradition in science and can open a conversation about history in our classrooms and fields, but it is also worth noting that the history is very biased to celebrate a certain demographic of people. The American Ornithological Society recently decided to remove such memorializations and began an effort of renaming many birds to be more descriptive (Council of the American Ornithological Society 2023). Our society may also consider such revision in the future, but no such changes were made to the current list.

High-Profile Plants to Illustrate the Difficult Decisions Faced by the Committee

Especially for weeds that are particularly common or difficult to control, and thus are widely studied and referenced within the WSSA, the occurrence of multiple common names for a single species can be a hindrance to compiling research results for meta-analyses, writing informative herbicide labels, and advocating for public support and federal funding. We highlight here just four plant species that represent some of the difficulty the committee had in reviewing the entire list of names.

Palmer amaranth (Amaranthus palmeri S. Watson)

Over the past 30 years, Amaranthus palmeri has become one of the most well-known agricultural weeds in the United States (Ward et al. Reference Ward, Webster and LE2013). It is an annual warm-season (C₄) dioecious (separate male and female plants) forb native to the arid southwestern United States, including southern California, New Mexico, and Texas, as well as northwest Mexico (Sauer Reference Sauer1957). In its native range, A. palmeri is considered a culturally important plant species by indigenous populations including the Cocopa, Navajo, Pima, Yuma, and Mohave, who utilized the seed and greens for their high protein and fat content (Kindscher et al. Reference Kindscher, Martin, Corbett and Lafond2018). This species quickly produces a large amount of biomass and a prolific amount of seed per plant (up to 500,000) and is known to have developed herbicide resistance in part due to its genetic plasticity and fecundity (Roberts and Florentine Reference Roberts and Florentine2022). These characteristics likely caused the species to expand beyond its native range with seeds accidentally dispersed through the crop and seed trade. This species became a problematic weed in U.S. agriculture in the early 1990s (Ward et al. Reference Ward, Webster and LE2013). The emergence of A. palmeri as a major agronomic weed is relatively recent, as it was not listed among the most troublesome weeds in a 1974 survey of the southern United States (Buchanan Reference Buchanan1974); its first appearance in the annual survey of the Southern Weed Science Society occurred in 1989 (Webster and Coble Reference Webster and Coble1997). Today Palmer amaranth is listed as one of the most, if not the most, economically damaging weeds in corn, cotton, sweet potatoes, and soybean in the United States (https://wssa.net/weed/surveys/).

Although this troublesome weed is so widespread, Palmer amaranth is known by many alternative common names such as carelessweed, Palmer’s amaranth, dioecious amaranth, and pigweed. The scientific name, Amaranthus palmeri S. Watson, is found on a total of 460 herbicide labels, with the common name “Palmer amaranth” found on 405 labels, the common name “carelessweed” found on 94 labels, and both common names listed on 39 herbicide labels (Table 3). Typically, “Palmer amaranth” is the common name used by the agricultural community, whereas in nonagricultural areas, this species is commonly referred to as “carelessweed,” which is the common name listed for the species in the USDA PLANTS database. This distinction can be confusing, especially to people trying to control Palmer amaranth. Herbicide labels, scientific and extension publications, and plant databases are not always aligned on the naming of a species, and this may lead to future problems. Palmer amaranth is retained as the WSSA-recognized common name and has been submitted as a synonym for A. palmeri in the PLANTS database.

Table 3. Search terms related to three weeds and the number of search results in different databases

^a Asterisk (*) denotes word that is not a synonym but may be a search term used.

^b https://agrian.com. Accessed: September 26, 2023.

^c https://www.cdms.net/labeldatabase/Advanced-Search. Accessed: September 26, 2023.

^d https://www.cambridge.org/core/jour-ls/weed-science. Accessed: September 26, 2023.

^e https://www.cambridge.org/core/jour-ls/weed-technology. Accessed: September 26, 2023.

Implications of WSSA Having a Composite List of “Weeds”

Recognizing that there are implications to publishing a database on the Internet listing standard names for weedy plant species, the Standardized Plant Names Committee has aspirations to improve the usefulness of this list for our members and reduce confusion to outsiders that come across our list. A list of several thousand plants cannot be assumed to be “weedy” in every habitat, but at the same time, most plants could be in need of management or control under certain circumstances and need to be listed on herbicide labels. One way to address this is to refer to the CLW as a list of plants that have the potential to be considered as “weeds” commonly encountered in vegetation management. An explanation or disclaimer can be stated on the public web page to clarify the broad approach through which plants have been added to the list. Even an explanation of “weediness” might not be enough, as in some conservation efforts, plants with weedy traits such as aggressive establishment might be important pioneer species and yet not be inhibitory to further native establishment.

While there have been attempts to change names that were disparaging, there are categories of names that may yet be perpetuating unintentional marginalization, especially when names are not indicating a true country of origin but have become associated with some stereotype.