Great Basin Naturalist

Volume 42 Number 1 Article 13

3-31-1982

Paspalum distichum L. var. indutum Shinners ()

Kelly Wayne Allred New Mexico State University, Las Cruces, New Mexico

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Recommended Citation Allred, Kelly Wayne (1982) " distichum L. var. indutum Shinners (Poaceae)," Great Basin Naturalist: Vol. 42 : No. 1 , Article 13. Available at: https://scholarsarchive.byu.edu/gbn/vol42/iss1/13

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. PASPALUM DISTICHUM L. VAR. INDUTUM SHINNERS (POACEAE)'

Kellv Wayne Allred-

distichum from the .\bstract.- Glabrous Paspalum distichiim, pubescent var. indutum, and pubescent of P. exist between the three western United States were compared. No morphological differences other than pubescence western regions. The var. forms. Plants from the eastern United States are generally more glabrous than those from indittum represents an extreme pubescent form and is reduced to synonymy under P. distichum.

is also Paspalum distichum L.' is the familiar out the southern states. Knotgrass "knotgrass" of swamps, swales, marshes, widespread in other warm-temperate to trop- ditches, and muddy sites throughout much of ical regions of the world. Texas, with the continental United States. It grows along Material from Dallas County, both eastern and western coasts and through- strongly hirsute sheaths and blades was Branch 9 Abaxial Blade 10 Panicle 2 Collar Hair Length 1 Node Pubescence Hair Density Number

4 Sheath Back Length 3 Sheath Margin 11 Panicle Internode 12 Branch Hair Density Hair Density Length

6 Blade Length Length 5 Ligule Length 13 Rachis Width 14 Spikelet

Adaxial Blade 1 Length 7 Blade Width 15 Spikelet Width 16 Glume Hair Density

of the means (vertical line), Figs. 1-8. Comparisons of the means (vertical line), Figs. 9-16. Comparisons and one standard deviation on range (horizontal line), and one standard deviation on range (horizontal line), (horizontal bar) for three forms of each side of the mean (horizontal bar) for three forms of each side of the mean D, glabrous distichum form; I, pub- Paspalwn distichium. D, glabrous distichum form; I, Paspalum distichum. western form. The pubescent indutum form; W, pubescent western form. escent indutum form; W, pubescent labeled. The features measured are as labeled. features measured are as

University, Las Cruces, New Mexico 88003. 'Journal Article 90.3, Agricultural Experiment Station. New Mexico State Mexico 88003. ^Department of .'Vmmai and Range Sciences, New Mexico State University, Las Cnices, New (Michx.) Scribner. this involving also the names P. vaginatum Sw. and P. pa^alodes There is current controversv concerning the application of name, See also Guedes (1976) and Renvoize and Clayton (1980). Until this matter is resolved, I will use -p distichum" in the sense of Hitchcock (1951).

101 102 Great Basin Naturalist Vol. 42, No. 1

described by Shinners (1954) as Paspalum dis- sentative sample of this taxon. From this Hchum var. indutum. The variety indutum sample, 235 specimens were examined and has been known only from the type locality measurements taken for the following fea- and a few collections in the same county. tures: node pubescence, collar pubescence Many plants of P. distichum from the western (length and number of hairs), sheath margin United States, however, including the inter- pubescence (density), sheath back pubescence mountain region, also possess varying degrees (density), ligule length, blade length, blade of pubescence on the sheaths and elsewhere. width, adaxial blade pubescence (density), This fact suggested the following queries. abaxial blade pubescence (density), number How does the var. indutum compare with of branches, length of the up- the typical glabrous material of var. dis- permost internode of the inflorescence, up- tichum, and with the pubescent material of permost branch length, rachis width, spikelet the western United States? Are there other length, spikelet width, and first glume length. features in addition to pubescence that serve Pubescence "density" was measured by the to distinguish any of the three forms? What is number of hairs touching or intersecting a the geographic distribution of these forms? standard 1 cm micrometer grid at 40X mag- How many taxa are involved in this complex? nification. To help evaluafe the relative de- gree of pubescence, a Pubescence Index (PI) Materials and Methods was calculated for each specimen. The PI was the sum of the values for the pubescence specimens were gathered from vari- features (node, collar, sheath margin, sheath ous herbaria throughout the United States back, adaxial blade, and abaxial blade). Total- range of Paspalum distichum to give a repre- ly glabrous plants would have a PI of zero.

18.0 10.4

Fig. 17. Pubescence Index values of selected species of Paspalum distichum based on measurements of node pu- ]'"''' '"?' ^'" ^^'' ^'"^"'y' '^'""'^ ^^'^ ^^'' ^^"^i^y- ^d^^'^' blade hair density, and ab- axlTbS.'haxial blade fri? ""f hair density. Circled PI values represent the indutum form. The map is not intended to representcm theu.c gege- ographic distribution of P. disfic/j urn. ^ March 1982 Allred: Paspalum (Poaceae) 103

were plotted geo- with greater PI vakies corresponding to in- specimens of knotgrass remaining 74 creased pubescence. graphically (Fig. 17). (The specimens of the original 235 represented ei- ther duplicates or other specimens with iden- Results and DiscliSsion tical PI values and from the same localities as Specimens that Most characteristics of Paspalum distichiirn those plotted on the map.) the variety indutum, that are remarkably consistent throughout the were referable to sheaths and blades as continental United States. The three forms is, with densely hirsute SMU), (glabrous distichum, indittum, and pubescent in the type specimen {Shinners 10564, from western) are essentially identical for all mor- were found in widely separate localities PI range of phological features other than pubescence Texas to Washington and had a specimen of indutum had a (Figs. 1-16). Even slight differences, such as 25-79. The type the length of the panicle in ternode (Fig. 11) PI value of 74. a rough cline in pu- are not correlated with any other features. There appears to be plants The obvious differences illustrated by Figures bescence from more glabrous eastern to more pu- 1-16 are in the pubescence features, but (characteristic of distichum) Division of the United these are the result of the a priori classifica- bescent western forms. showed an average in- tion of the plants into three groups: glabrous States into regions eastern knot- distichum, pubescent indutum, and pu- crease in PI values from 2.8 for (Fig. The bescent western forms. grass to 18.0 for western plants 17). representing varie- The only possible differences, then, involve extreme pubescent forms interrelationship pubescence, which can be evaluated by the ty indutum showed no such distribution. High PI values Pubescence Index (PI). The PI values for 161 with geographic

distichum based on measurements of sheath back Fis 18 Pubescence Index values of selected species of Paspalum density. Circled PI values represent the mdutum hair density, adaxial blade hair density, and abaxial blade hair distribution of P. distichum. form. The map is not intended to represent the geographic 104 Great Basin Naturalist Vol. 42, No. 1

(7-8) in eastern plants were due mainly to in an east-west continuum, but there is no very pubescent nodes, collars, and sheath strong geographic distinction nor any feature margins, but the pubescence of western other than pubescence that would allow a plants involved not only the nodes, collars, taxonomic segregation. The variety indutum and sheath margins, but also especially the and other pubescent plants are best viewed sheath back leaf and blades. This is illustrated as pubescent forms of Paspalum distichum. in Figure 18, where modified PI values from only the sheath back and blade surfaces are plotted. We see that eastern plants are Acknowledgments glabrous or nearly so for these features Many thanks to the curators of the follow- (PI = 0.5), but western plants are often pu- ing herbaria for their generous loan of speci- bescent (PI = 9.5). The relationship, however, mens: BRY, FSU, NCU, SMU, UNM, UTC, is far from absolute, as is shown by the range and WTU. in PI for each region.

In conclusion, there is no morphological distinction between the nearly glabrous east- Literature Cited em knotgrass, the pubescent western forms, GuEDES, M. 1976. and the variety indutum. The variety in- The ease of Paspalum distichum and against futile name changes. Taxon diitum merely represents the extreme pu- 25(4):512. Hitchcock, A. S. 1951. Manual of the grasses of the bescent form of Paspalum distichum. Recog- United States. USDA Misc. Publ. 200. 2d rev. ed. nition of this taxon is untenable, with no basis Agnes Chase. in geographic distribution and no correlation Renvoize, S. a., and W. D. Clayton. 1980. Proposal to reject the name with any other suite of features. The limits of Paspalum distichum L. Taxon 29(3/4):339-340. such a taxon would be entirely arbitrary. Shinners, L. 1954. Notes on north Texas grasses. Rho- Pubescence patterns in knotgrass do appear dora 56:31-32.