Systematic Botany (2007), 32(1): pp. 60–70 # Copyright 2007 by the American Society of Plant Taxonomists An SEM Survey of the Leaf Epidermis in Danthonioid Grasses (Poaceae: Danthonioideae) ELIZABETH REIMER and J. HUGO COTA-SA´ NCHEZ1 Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan S7N 5E2 Canada 1Author for correspondence ([email protected]) Communicating Editor: Wendy B. Zomlefer ABSTRACT. This study comprised a scanning electron microscope survey of abaxial epidermal features in subfamily Danthonioideae, with emphasis on North American Danthonia. The survey included 21 taxa, encompassing seven genera (Austrodanthonia, Cortaderia, Danthonia, Merxmuellera, Notodanthonia, Rytidosperma, Tribolium) and the eight North American Danthonia species. We investigated micromorphological characters to determine taxonomic utility and whether North American representatives of Danthonia are distinct. We examined micromorphological epidermal features: macrohairs, bicellular microhairs, prickle hairs, silica bodies, and stomata. We found no distinguishing characters at the subfamilial level. Danthonia is characterized by the absence of abaxial stomata and presence of bicellular microhairs with basal and terminal cells of equal length and microhairs with long basal cells relative to terminal cells. Prickle hairs in the abaxial epidermal costal regions of four species of North American Danthonia are reported for the first time. KEYWORDS: Danthonioideae, epidermal characters, macrohairs, microhairs, prickle hairs, silica bodies. The Danthonioideae (Poaceae) comprise a single Stapf. (Barker et al. 2003) and Merxmuellera Conert tribe, Danthonieae, with approximately 250 species (Barker et al. 2000), are para- or polyphyletic. and 19 genera [Grass Phylogeny Working Group Historically, the generic circumscription of (GPWG) 2001]. The subfamily occurs predomi- danthonioid grasses, in particular Danthonia DC., nantly in the Southern Hemisphere and is consid- has been controversial due to the large number of ered south-temperate, but the greatest diversity is species worldwide and the wide overlap of found in Africa (nine genera and 125 species). In morphological attributes. The latest studies recog- the Australian grasslands of New South Wales, nize nine species in South America, eight in North Victoria, and Tasmania, danthonioid grasses America [D. californica, D. compressa, D. decumbens, frequently form the dominant vegetation cover D. intermedia, D. parryi, D. sericea, D. spicata, and D. and are economically important as native forage unispicata (Darbyshire 2003)], three in Europe, two species. in Africa, and two in Asia (Linder and Verboom Danthonioideae were formerly included in 1996). Of these, one species (D. decumbens) is native Aveneae (Hubbard 1934) or within Arundinoi- to Europe but is naturalized in North and South deae, a mix of unrelated taxa that do not fit into America and Australia (Darbyshire 2003) for a total other subfamilies (Watson and Dallwitz 1992). of 23 species (Linder and Verboom 1996). Molecular evidence supports the polyphyly of Early morphological studies of Danthonia re- Arundinoideae s.l. (Barker et al. 1995, 1999) vealed an extensive range of interspecific variability and the recognition of Danthonioideae at the and highlighted the need for a new taxonomic subfamilial level as a distinct lineage from Ar- scheme (deWet 1954, 1956). The taxonomic rearran- undinoideae (GPWG 2001). The monophyly of gement of Danthonia s.l. began with the formal Danthoniodeae is supported by morphological establishment of Chionochloa Zotov, Notodanthonia and molecular data. Haustorial synergids, Zotov, Erythranthera Zotov, and Pyrranthera Zotov to bilobed prophylls, and ovaries with distant describe the New Zealand taxa (Zotov 1963). In the styles are subfamilial synapomorphies (Linder following decade the South African taxa were and Verboom 1996). In addition, several circumscribed within the genera Dregeochloa Conert characters from the chloroplast genome provide (Conert 1966), Karroochloa Conert & Tu¨ rpe (Conert strong evidence for monophyly (Barker et al. and Tu¨ rpe 1969), Merxmuellera Conert (Conert 1970), 2003). Currently, the phylogenetic position and Pseudopentameris Conert (Conert 1971). Nicora of this subfamily is within the Panicoideae- (1973) placed several South American taxa in the Arundinoideae-Centothecoideae-Chloridoideae- genus Rytidosperma Steud. Furthermore, Conert Aristidoideae-Danthonioideae (PACCAD) clade (1987) argued that the basis for the separation of and sister to Aristidoideae (GPWG 2001). Though the Australian taxa from the genus Danthonia was Danthonioideae are monophyletic (GPWG 2001), unfounded because the lemma hair characters used several genera in the subfamily, including Cortaderia to separate them from Danthonia s.l. were inconsis- 60 2007] REIMER & COTA-SA´ NCHEZ: SEM OF DANTHONIOID GRASSES 61 tent. More recently, Linder and Verboom (1996) characters using scanning electron microscopy advocated the recognition of Austrodanthonia H. P. (SEM) to investigate East African grasses (Palmer Linder, Joycea H. P. Linder, Notochloe Domin., and and Tucker 1981, 1983; Palmer et al. 1985; Palmer Plinthanthesis Steud. to describe Australasian and Gerbeth-Jones 1986, 1988) have proven the danthonioid grasses and recognized the African taxonomic and phylogenetic utility of this tech- genus Schismus P. Beauv. The same study supported nique, which provides detailed three-dimensional separation of Danthonia and Rytidosperma based on views. SEM has also been important in investigat- morphological and anatomical data, such as the ing the morphology of silica bodies, a common presence of tufted lemma hairs in Rytidosperma and type of phytolith in plants. These structures are cleistogamous florets in the upper leaf sheaths of mineral deposits that form inside specialized Danthonia. A more recent re-examination of the epidermal cells in the Poaceae (Piperno and relationships within danthonioid grasses identified Pearsall 1998). The significance and implications seven informal groups: the basal Merxmuellera of silica bodies in the taxonomy of grasses have assemblage and the Pentaschistis, Pseudopentameris, been widely addressed. Certain silica body shapes Chionochloa, Cortaderia, Rytidosperma, and Danthonia are characteristic of grass subfamilies and tribes. clades (Barker et al. 2000). Previous studies have examined leaf blades in Despite the extensive work in para- or poly- other genera and species within Danthonioideae phyletic taxa, such as Merxmuellera and Cortaderia, (Ellis 1980a, 1980b, 1985; Barker and Ellis 1991; the intrageneric taxonomic boundaries in the sub- Barker1993,1995);however,severalrelevant family remain unclear (Barker et al. 2000, 2003). taxonomic and phylogenetic questions remain Likewise, studies of the subfamily have not in- unanswered. Due to taxonomic complexity, the cluded sufficient taxonomic sampling within paucity of morphological synapomorphies, and the Danthonia to adequately test its monophyly. Wright relatively unexplored micromorphological struc- (1984) suggested that Danthonia is monophyletic, tures, we undertook an SEM survey of epidermal but the morphological and anatomical traits sup- features in danthonioid representatives with em- porting the clade, such as scattered lemma hairs, phasis on North American representatives of the costal short cells in rows, undivided phloem, and genus Danthonia to identify potentially informative the presence of bulliform cells, are not unambig- characters. Our primary objectives were 1) to uous synapomorphies. More recently, two synapo- investigate micromorphological characters to as- morphies have been reported for Danthonia, the sess their taxonomic value at the generic and presence of cleistogenes in the lower leaf sheaths specific levels and 2) to determine whether the and a base chromosome number of x 5 18 (Linder North American representatives of Danthonia can and Verboom 1996), but there are some exceptions. be distinguished based on microstructures of the For example, cleistogenes are rarely present in D. leaf epidermis. Our study represents the first intermedia (Darbyshire 2003), and an unusual formal SEM examination of leaf epidermal char- chromosome count of 2n 5 31 was reported in D. acters of danthonioid grasses. spicata (Darbyshire and Cayouette 1989). Over the last four decades, micromorphological MATERIALS AND METHODS characters of the leaf epidermis have been scruti- Taxonomic Sampling. Twenty-one taxa, including seven nized in several plant groups. These attributes danthonioid genera (Austrodanthonia, Cortaderia, Danthonia, have been informative at various taxonomic levels Merxmuellera, Notodanthonia, Rytidosperma, Tribolium Desv.) as recognized by Barker et al. (2000) were investigated in this and valuable to differentiate among groups of study (Appendix 1). Our sampling encompasses the eight extant taxa with putative relatives available in the North American Danthonia species: D. decumbens [syn. fossil record (Stace 1984). Watson and Dallwitz Sieglingia decumbens (L.) Bernh.] introduced from Europe, (1992 onwards) report detailed descriptions of the and the seven native species (D. californica, D. compressa, D. intermedia, D. parryi, D. sericea, D. spicata, D. unispicata; leaf epidermis in numerous taxa, emphasizing the Darbyshire 2003). In addition, D. filifolia [syn. Danthonia significance of these characters in the systematics secundiflora subsp. secundiflora J. Presl.], a