Lemma Epidermal Features in the North American Species of Melica and Selected Species of Briza, Catabrosa, Glyceria, Neostapfia, Pleuropogon, and Schizachne (Gramineae)

Abstract

A scanning electron microscopical survey of the lemma epidermal features in the 17 North American species of Melica and selected species of Briza, Catabrosa, Glyceria, Neostapfia, Pleuropogon, and Schizachne is presented. Melica is characterized by the universal presence of numerous hooks (=barbs, crown, or crochet cells of authors) alternating with long cells with straight to slightly undulating walls. Prickles also occur in all taxa, but their size, shape, and abundance were variable, both between and, in one case, within species. Macrohairs and stomatal complexes were occasionally observed on species of Melica, but silica bodies were not found on any of the species. Lemma epidermal features of Briza, Catabrosa, Glyceria, Pleuropogon, Schizachne, and Neostapfia suggest that Melica, Catabrosa, Glyceria, and Pleuropogon may be closely related but that the genera Briza, Schizachne, and Neostapfia are distinct from this group. Melica is a grass genus of ca. 60 species found throughout temperate and cooler regions of both hemispheres (Gould and Shaw 1983). Of these, 17 occur in North America, primarily in the west and northwest, although two species are widespread in the eastern and southeastern United States. Melica is characterized by a number of features, including closed sheaths, frequently swollen corm-like culm bases, and rounded, usually 7-nerved lemmas with hyaline apices and upper margins (Boyle 1945). Other diagnostic features include relatively large thin glumes that are less firm than the lemmas, and several florets in each spikelet with the upper florets often reduced to a knob-like rudiment. Extensive studies of the micromorphology of spikelets in the Gramineae have confirmed that their epidermal features can help to elucidate taxonomic relationships. Shaw and Smeins (1981) showed that epidermal characteristics of the callus supported recognition of three groups of Eriochloa taxa. Clark and Gould (1975) demonstrated that palea epidermal characteristics could be used to reveal taxonomic relationships among genera in the Paniceae. Several authors have used lemma epidermal patterns to demonstrate relationships among modern grasses, including Agrostis and related genera (Bjorkman 1960), Panicum (Hsu 1965), and Stipa (Thomasson 1981). I have used lemma epidermal features to reveal phylogenetic trends among fossil and related modern grasses in the tribes Stipeae (Thomasson 1978a, 1978b, 1980b), Paniceae (Thomasson 1978b), and Oryzeae (Thomasson 1980a). A study of the lemma epidermal pattern of several species of Melica originally was undertaken as an aid in identifying unknown fossil grasses and in determining if similarities and dissimilarities in the epidermal patterns existed. The investigation was later extended to include a limited number of species from genera that have been allied with Melica by various authors (see Discussion and Conclusions of this paper). MATERIALS AND METHODS Lemmas were removed from herbarium specimens, cleaned in xylene in an ultrasonic cleaner for 1 hour to remove epicuticular wax and surface debris, air dried, then attached to small brass discs with high purity silver paint and coated with 60% Au/40% Pd in a Structure Probe Incorporated sputter coater. At least 2-3 mature lemmas were examined from one (in all but Briza media two or more) to four collections of each taxon in an ISI Super IIIA or SX-30 SEM at 15 kV and a working distance of 23 mm. Although all epidermal features observed are noted in table 2, only those of the middle portion of the lemmas were photographed for purposes of standardization. Terminology for