Cheatgrass: Fire and Forage on the Range

Chapter 12. Revegetation Plant Material

To this point we have referred to crested wheatgrass in general terms as if it were a homogeneous species. In fact, the taxonomy of crested wheatgrass is quite complex. Dr. Douglas Dewey of the Agricultural Research Service (ars) spent much of his career developing a genomic system of classification for the perennial species of the grass tribe Triticeae (for classification purposes, large plant families are subdivided into tribes).1 There are about 250 perennial species in the Tribe Triticeae, including many of the world’s important forage and crop species. Annual grasses within this tribe include the crops wheat, barley, and rye. As grasses within the Triticeae evolved through interspecific hybridization, they may have acquired different genomes (the term “genome” refers to one haploid set of chromosomes) and then gone through further hybridization. Understanding the genomic structure of the grasses of Triticeae has made it possible for plant breeders to select new plant material from among the members of the tribe for cultivar development. Throughout his career, Dr. Dewey was besieged with demands for new plant material for revegetation of Great Basin rangelands, but he refused to be distracted from his taxonomic research. As he mastered the international literature of grass genetics and classification (much of which is in Russian), he revised the scientific names of many of the major grasses of the western range. For example, the extremely widespread dominant bluebunch wheatgrass, chapter 12 Revegetation Plant Material 183 184 c h e a tg r a s s originally described by Pursh from material brought back by Lewis and Clark, went from Agropyron spicata (Pursh) Scribner & Smith to Pseudoroegneria spicata (Pursh) Löve. The good old cowboys working as technicians out on the range howled, “Sacrilege!” when that happened. They had recorded the shorthand identification “AgSpic” (abbreviating the genus and species names) a million times. Dr. Dewey became quite defensive during the later years of his career, especially when addressing audiences containing substantial numbers of range managers, but students are now writing Pseudoroegneria spicata on the inside of their wrists so they can pass laboratory examinations in range plant identification courses. Dewey summarized the problems he encountered in classifying crested wheatgrass as follows: “The taxonomic history of crested wheatgrass reflects widespread confusion and uncertainty. Any expectation of a simple and neat solution to crested wheatgrass taxonomy is unrealistic because the problem is inherently complex, and subjective judgements must be made. Multiple chromosome races and the ability of crested wheatgrass taxa to hybridize are the root of the taxonomic problems. All crested wheatgrass taxa can be hybridized with each other, and many taxa hybridize with ease and produce fertile offspring.”2 Crested wheatgrasses occur at three “ploidy” levels: diploid (2n = 14), tetraploid (2n = 28), and hexaploid (2n = 42). That is, individuals may have two, four, or six sets of chromosomes. The tetraploids are the most common and span the entire natural distribution range of crested wheatgrass in Europe and Asia. Diploids occur from Europe to Mongolia as sporadic islands in the general distribution of the tetraploids. Hexaploids are very rare, occurring only in northeastern Turkey and northwestern Iran.3 Tetraploid strains are the most commonly seeded types in North America, where they are represented by the group called Standard crested wheatgrass. Standard is not a plant classification or formal taxonomic name; it was made up by the Montana Seed Growers Association to describe the type of crested wheatgrass they were harvesting and selling.4 Under the broadly used category “Standard” are the cultivars Nordan, Summit, and Ephraim. When plant breeders formally release plant material for use in agriculture, they describe it and assign a name; these releases are known as cultivars. In scientific writing, cultivar names are enclosed by single quote mark, but technically , the use of single quotation marks along with the word “cultivar” r e v e g e ta t i o n p l a n t m a t e r i a l 185 is redundant. The diploid forms of crested wheatgrass are grossly classified under the trade name Fairway, which is equivalent to Standard. There are two cultivars, ‘Parkway’ and ‘Ruff.’5 Dewey proposed the following scientific names for the introduced crested wheatgrasses found in North America: (1) diploid forms of Agropyron cristatum are fairway crested wheatgrass (Dewey suggested not capitalizing “fairway ” to help avoid confusion with the cultivar name, and we follow that usage from this point on), (2) tetraploid forms...