Reprinted from the Soil Science Society of America Proceedings Vol. 33, no. 1, January-February 1969 677 South Segoe Road, Madison, Wisconsin 53711 USA Purchased by Agricultural Research Service, U. S. Department of Agriculture, for official use. Morphological Classification of Grass Phytoliths ' P. C. Tw~ss,ERWIN SUESS, AND R. M. SMITH^ ABSTRACT FTER ESTABLISHING a network of dust traps at 15 sta- tions east of the Rocky Mountains in which continu- Opal phytoliths derived from epidermal cells of grass leaves A ous dust deposition was analyzed each month (2S), it was have been identified in atmospheric dust, soils, paleosols, observed that opal phytoliths from grasses were a minor Pleistocene loess, and deep-sea sediments. By comparing ori- ented shapes of phytoliths in spodograms of 17 common grass but ubiquitous constituent of the greater than 2-micron species, four classes and 26 types are proposed which distin- fraction. The opaline silica bodies that accun~ulate in guish three groups of subfamilies of Gramineae. The Festucoid epidermal cells of leaves of the grass family have many class contains eight types that are circular, rectangular, ellip- shapes and have been identified in atmospheric dust (4, 8. tical, or oblong forms. The Chloridoid class contains two types 9),3 in soils (1, 2, 5, 6, 16, 17, 24, 26, 27, 28), in paleosols of saddle-shaped bodies. The Panicoid class contains 11 types (6),4*5in Pleistocene loess and other ancient sediments (3, that are variations of crosses and dumbbells. The Elongate class 15) and in deep-sea cores ( 18). contains five types that have no subfamily implications and Suess5 in a pilot study, recognized that phytoliths from occur in all 17 species. Because phytoliths of native tall grasses short grasses in western Kansas were different from those ( Panicoid ) , short grasses (Chloridoid ), and common domestic in tall grasses of eastern Kansas and that phytoliths in grasses of the humid regions (Festucoid) can be distinguished, it is possible to determine whether ~hytolithsin dust, soils, and atmospheric dust could be traced to these two groups. The sediments were derived from local or remote sources. number of grass species has been expanded and a classifi- cation of grass phytoliths, based on grass taxonomy, is Additional Key Words for indexing: opal phytoliths, silica proposed that can be used as an indicator of provenance bodies. for land-derived sediment. Micromorphology of Grasses Contribution from the Soil and Water Conservation Re- search Division, ARS, USDA, in cooperation with the Kansas Prat (20, 21, 22, 23) used several microscopic char- Agr. Exp. Sta. and the Departments of Geology and Agronomy, acteristics of the epidermis in describing many grass spe- Kansas State University. Department of Agronomy Contribu- cies. He distinguished three categories of elements in the tion no. 1039. Received June 3, 1968. Approved July 8, 1968. grass epidermis: (i) differentiated elements, (ii) funda- ! Geologist, USDA, Manhattan, Kans.; Assistant Oceanog- rapher, University of Hawaii, formerly Graduate Assistant, mental elements, and (iii) bulliform elements. Differen- Department of Geology, Kansas State University; and Profes- tiated elements consist of silica cells, exodermic ele ents sor, Agronomy Department, West Virginia University, formerly Research Soil Scientist, USDA, Manhattan, Kans., respectively. (hairs and spicules), cork cells (subereous cells) 3nd R. K. Krauss, 1967. The influence of atmospheric dust upon stomata. Fundamental elements are epidermal cells that the Florence soils of eastern Kansas. M. S. Thesis. Kansas State University, Manhattan. are greatly elongated, parallel to the long axis of the leaf. D. S. Pease, 1967. Opal phytoliths as indicators of paleosols. They are nearly uniform and have few specific characters. M, S. Thesis. New Mexico State University, University Park. By showing the distribution of these three elements in the ~r .' E. Suess, 1966, Opal phytoliths. M. S. Thesis. Kansas State University, Manhattan. grass leaf with a dermogram, Prat recognized three sub- 110 SOIL SCI. SOC. AMER. PROC., VOL. 33, 1969 SILICA BODIES IN ABAXIAL LEAF EPIDERMIS families: Bambusoideae, Panicoideae, and Festucoideae. OF 1E9 MAVS In Panicoideae he included the eu-panicoid type and the ------------ chloridoid type. MICROHAIR BASE Metcalfe (19) also used micromorphology in describing INTER - RSTOMATAL CELL (I.C.) 345 genera of grasses. Though stating that the leaf con- COSTAL tains the most important diagnostic characters, he warned ZONE LONG CELL (p. XXXIV) that (i) minor anatomical variations occur in a single leaf blade, (ii) structural variations occur ----Y---- SHORT CELL (SILICA) VEIN among leaves from different layers in an individual plant, SHORT CELL (CORK) and (iii) leaves from plants of a single species can also ------------ vary among habitats. The diagnostic epidermal characters -LONG AXIS OF LEAF EPIDERMIS- that he used were shapes of (i) short cells and silica Fig. 1-Spodogram of Zea mays L. (after Metcalfe, 1960). bodies, (ii) macrohairs, (iii) microhairs, (iv) prickle hairs, (v) papillae, (vi) stomata, and (vii) long cells. Previous Classifications Metcalfe, like Prat, recognized three major taxonomic groups: (i) Bambusoid, (ii) Festucoid, and (iii) Panicoid. In addition to morphological classifications of grass The bamboos and related genera are clearly distinct from plants, several classifications based on shape of silica all other grasses. Using leaf structure, he subdivided the bodies derived from epidermal cells have been proposed. Festucoid and Panicoid groups into several tribes. Ehrenberg (8) examined several samples of dust from the Distribution of epidermal cells in the grass leaf is illus- eastern hemisphere that fell on land and in the sea and pro- trated by a generalized section of the leaf of corn (Zea posed 10 genera and 90 species of Phytolitharia. He did mays L.) in Fig. 1. Siliceous epidermal cells in most not attempt to relate them to particular grasses. Folger et grasses are of two distinct sizes, elongate and short. Elon- al. (9), in their study of a North Atlantic dust fall, stated gate cells with the long axes parallel to the length of leaf that the phytoliths were derived from grasses. They revived include the "long cells" and interstomatal cells of Metcalfe. Ehrenberg's classification by listing two genera and eight Length, wall thickness, and surface ornamentation of long species. cells are diverse. Ends of interstomatal cells are concave Smithson (28) compared opal phytoliths in some British where they fit around stomata, whereas ends of long cells soils with the siliceous epidermal cells of grasses growing are nearly straight. at the same locations. He recognized six shapes and could Short cells are nearly equidimensional and are classed distinguish between Festucoid and Panicoid forms. as either "silica cells," where each is nearly filled with a Baker (1) proposed a nomenclature for opal phytoliths single silica body or as cork cells, where they act as cork; based on the anatomy of grasses and allied plants; how- however, some cork cells may contain silica. The shape of ever, he did not trace phytoliths to the particular taxonomic silica bodies in cells may not correspond to the shape of the unit from which they were derived. enclosing cell. In grass taxonomy the shape, frequency, and distribution of silica bodies in short cells of the mature leaf PROCEDURE are combined with other properties of the epidermis in To trace discrete phytolith grains that occur in sediment to identifying species and genera. a particular taxonomic group in the Gramineae, 17 species rep- Table 1-Taxonomic groups and occurrences of grasses studied Taxonomic groups Tribe Prat (20) and Species of grass Common name (13) Metcalfe (19) Occurrence Bromus inermis Leyss. Smooth brome Festuceae Festucoid Domestic Festuca elatior L. Meadow fescue Festuceae Festucoid Domestic & pratensis L. Kentucky bluegrass Festuceae Festucoid Domestic Triticum aestivum L. Wheat Hordeae Festucoid Domestic Aristida sp. L. Three-awn Agrostideae Festucoid Mountains, Trans- Pecos, Texas Bouteloua curtipendula Side-oats grama Chlorideae Panicoid 7 (Michx. ) Torr. "Short grass" Bouteloua gracilis (H. B .K .) Blue- grama Chlorideae Panicoid region or prairie Lag. and Steud. vegetation, Western Kansas. --Bouteloua hirsuta Lag. Hairy grama Chlorideae Panicoid Buchloe dactyloides (Nutt. ) Buffalograss Chlorideae Panicoid - Engelm. Bambusa sp. Bamboo Bambusadeae Bambusoid Domestic, Austin. Texas --Sorghum vulgare Pers. Grain sorghum Andropogoneae Panicoid Domestic --Panicum virgatum L. Switchgrass Paniceae Panicoid "Tall grass" Andropogon gerardi Vitman Big bluestem Andropogoneae Panicoid region or true -- prairie vegetation Andropogon scoparius Michu. Little bluestem Andropogoneae Panicoid of eastern Kansas. Sorghastrum-- nutans(L. ) Nash Indiangrass Andropogoneae Panicoid I- Zea mays L. Indiancorn Maydeae Panicoid Domestic Hilaria mutica(Buckl. ) Benth. Tobosagrass Zoysieae Panicoid Water Valley, Texas TWISS ET AL.: MORPHOLOGICAL CLASSIFICATION OF GRASS PHYTOLITHS 111 resenting three of the groups of Prat and Metcalfe were studied have given it equal rank with the other morphological (Table 1). classes. Two or three leaves from mature plants of each species were individually hand-washed several times in distilled water and dilute HCl to remove any mineral particles on the surface and to soften the mineralized tissue. The leaves were then placed in I) Festucoid Class , a ceramic