Andropogon elliottii

Weakley, Alan S., LeBlond, Richard J., McMillan, Patrick D., Sorrie, Bruce A., Poindexter, Derick B., Fuller, J. Brandon, Bridges, Edwin L., Budach, Brett J., Carr, Susan C., Crowl, Andrew A., Manos, Paul S., Fritsch, Peter W., Orzell, Steve L., Wipff, Joseph K., Messec, Lilly Anderson, Dellinger, Bob, Ungberg, Eric A., Yawn, Noah D., Cressler, Alan M., Oberholster, Chris, Barger, T. Wayne, Carter, J. Richard, Floden, Aaron J., Knapp, Wesley M., Copen, Iris, Jenkins, Amy M., Hughes, Ethan L., Annis, Jenna, Baker, Wilson & Mears, Randy L., 2024, Studies In The Vascular Flora Of The Southeastern United States. X, Journal of the Botanical Research Institute of Texas 18 (1), pp. 17-77 : 53-54

The Andropogon elliottii complex: refined concepts and description of a cryptic species Primary authors: Brett J. Budach and Edwin L. Bridges

Vorontsova et al. (2023) reestablished the genus Anatherum P. Beauv. for the former sect. Leptopogon Stapf within the broader genus Andropogon L. This required numerous new combinations for almost all North American Andropogon . While many of these combinations were made in Vorontsova et al. (2023), several recently described or elevated Andropogon species were left in need of new combinations within Anatherum P. Beauv. This need prompted a closer investigation of members of Campbell’s (1983) concept of Andropogon gyrans Ashe and provided an opportunity to redefine concepts therein.

From Andropogon subtenuis Nash to Anatherum gyrans (Ashe) Voronts. & E.A. Kellogg

Without much discussion, Campbell (1983) lumped Andropogon subtenuis Nash (1912) into his concept of Andropogon gyrans Ashe. It was not until recently that the name reappeared in Weakley’s Flora of the Southeastern US ( Weakley & Southeastern Flora Team 2023). There have been variable applications of the concept for A. subtenuis Nash , which lack obvious patterns and often do not match the type material. At one end of this concept are plants that do not match the type of A. subtenuis Nash and more closely resemble typical A. gyrans , with widened upper stem sheaths obscuring at least some racemes, but with extremely narrow basal leaves, glabrous basal leaf sheaths, and at least some exerted racemes. This application, as noted in Weakley and Southeastern Flora Team (2023), is assumed to include Campbell’s “tenuous variant” of his concept for A. gyrans . However, we have found that Campbell’s use of that designation was inconsistent with our contemporary applications of it. At the other end of the A. subtenuis Nash concept are plants that more closely match the A. subtenuis Nash type, lacking the wider stem sheaths and more obscured racemes of typical A. gyrans , but with similar dispersal unit characters and appressed-pubescent basal leaf sheaths. We believe that the former application of this concept is indeed patternable and descriptive of a true taxonomic entity while the latter only applies to a disturbance-induced growth form unique to cleistogamous grasses but is not taxonomically significant in and of itself.

The type specimen for Andropogon subtenuis Nash is clearly an example of a disturbance-induced anomalous growth form and not a taxonomically significant entity. With its long awns, long dispersal unit pubescence, wider leaf blades, and appressed-pubescent basal leaf sheaths, the type resembles typical A. gyrans material in every way aside from the extremely reduced stem sheaths and exerted racemes. This behavior of a typically cleistogamous grass shifting to chasmogamy in the presence of disturbance is not novel, indeed Campbell was aware of it ( Campbell 1982). Hitchcock and Chase (1950) also mention the possibility of Andropogon subtenuis Nash being a reduced, chasmogamous form of Andropogon elliottii Chapm. (= A. gyrans Ashe ). This is a phenomenon the authors have observed in other partially cleistogamous grasses, including Sporobolus clandestinus (Biehler) Hitchc. in north Florida and Sporobolus compositus (Poir.) Merr. in southwest Missouri, even though it is not well represented in the literature.

Following our examination of the type and interpretation of the potential for disturbance-induced anomalous growth forms, we believe that Campbell’s choice to lump Andropogon subtenuis Nash into his concept for Andropogon gyrans Ashe was correct. As such, our concept of Anatherum gyrans (Ashe) Voronts. & E.A. Kellogg includes the former Andropogon subtenuis Nash. Material recently identified as Andropogon subtenuis Nash using Weakley and Southeastern Flora Team (2023) could be either the anomalous, disturbance-induced growth form of Anatherum gyrans or the new species described below ( Anatherum subtile Budach & E.L.Bridges ).

From Andropogon gyrans Ashe ‘tenuous variant’ to Anatherum subtile Budach & E. Bridges

The concept of Andropogon subtenuis Nash as currently applied in Weakley and Southeastern Flora Team (2023) includes the named but not formally published concept of Campbell’s “tenuous variant” of Andropogon gyrans Ashe. However , upon close study of Campbell’s own annotations and descriptions, we found confusing applications. Campbell lumped A. subtenuis Nash into his concept of A. gyrans Ashe while maintaining the separate distinction of the “tenuous variant” of the same species in contrast to the “common variant.” Clearly these concepts were not meant to be applied to the same material. To further complicate this issue, a close study of the material that Campbell annotated as the “tenuous variant” of A. gyrans Ashe shows a very wide range of habitats and morphological expressions, relying only on what we believe to be wildly variable and unreliable characters related to the visibility and exertion of the racemes and raceme sheaths. There is certainly overlap between entities annotated by Campbell as the “tenuous variant” and “common variant.” There are also several Campbell-annotated sheets of what he called his “tenuous variant” that are clearly more like his “common variant” of A. gyrans Ashe and consistent with our updated concept of Anatherum gyrans (Ashe) Voronts. & E.A. Kellogg. Peduncle length and whether an individual plant is fully cleistogamous (all racemes hidden within the raceme sheaths; raceme sheaths hidden within the stem sheaths) or mostly chasmogamous (many racemes at least partially exerted from their sheaths; raceme sheaths well-exerted from the stem sheaths) are highly variable and respond dramatically to extreme forms of disturbance. Intensive field experience in both burned and degraded habitats throughout the state of Florida has shown that a severe late-season burn or recent roller-chopping or mowing can induce extreme chasmogamy in material that corresponds to either Campbell’s “common variant” or his “tenuous variant” of A. gyrans Ashe , and as such, it is not possible to perfectly and directly apply his “tenuous variant” concept to any one entity.

With that chaos of concepts and applications as a backdrop, we studied Floridian populations through meticulous field study of numerous individuals, with close attention paid to ecology and morphological responses to disturbances over time. An ongoing project studying growth and phenology responses to seasons of burning required the authors to locate and identify thousands of sterile vegetative individuals of over a dozen Anatherum species. This challenge allowed us to determine patterns in habitat and morphology that were initially unbiased by reproductive material or the use of existing keys and names. As the project proceeded, we were able to match these unbiased concepts with their reproductive characters and published names, and some striking patterns emerged. These patterns were repeatedly found in similar populations across numerous sites from the Florida panhandle to the Florida Everglades , helping construct more refined species concepts built on the marriage of morphology to ecology and biogeography. The result is, in part, the following description of a cryptic species: