The grass genera of the world
~ Muhlenbergia sensu lato
Including Spirochloe Lunell, Festuca arundincea Schreb.
Habit, vegetative morphology. Perennial; caespitose. Culms 20–45 cm high; herbaceous; unbranched above. Culm internodes solid, or hollow. Leaves non-auriculate. Leaf blades narrow; 0.7–2 mm wide (to 5 cm long); flat (or involute); without abaxial multicellular glands; without cross venation. Ligule an unfringed membrane.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches (stiff, slender divergent spikes, remote along a common axis); deciduous in its entirety (the central axis first elongating and coiling into a loose spiral); open. Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelets solitary; secund; biseriate (appressed to the concave sides of the triquetrous rachis); sessile; somewhat imbricate.
Female-fertile spikelets. Spikelets 3–4 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas (only slightly shorter than them); dorsiventral to the rachis (?); hairless; pointed; awnless; similar (lanceolate or acuminate, stiff, slightly divergent). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 1. Lemmas acuminate; similar in texture to the glumes to decidedly firmer than the glumes (firmly membranous, rigid); entire; pointed; awnless to mucronate; hairless (glabrous to scabrid); carinate to non-carinate; 3 nerved. Palea present; relatively long (glabrous); entire; awnless, without apical setae; textured like the lemma; rigid; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit small (2.5–3.5 mm long); fusiform. Hilum short (?). Pericarp fused (?). Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae over-arching the stomata (at one end); consisting of one oblique swelling per cell (at one end of each interstomatal, and on a few of the long-cells as well). Long-cells of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type (the basal cell somewhat the longer). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 51–52.5–57 microns long. Microhair basal cells 36 microns long. Microhairs 18 microns wide at the septum. Microhair total length/width at septum 2.9. Microhair apical cells (15–)18–19.5(–21) microns long. Microhair apical cell/total length ratio 0.29–0.41. Stomata common; (21–)22.5–24(–27) microns long. Subsidiaries predominantly triangular. Intercostal short-cells common; not paired (mostly solitary); not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows (but the files often interrupted by longish short-cells). Costal silica bodies present in alternate cell files of the costal zones; almost exclusively saddle shaped (a rather rectangular version); not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cells without a suberised lamella. PCR cell chloroplasts with well developed grana; centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs to nodular in section; with the ribs more or less constant in size (round topped). Midrib conspicuous (via its marked abaxial keel, and the bulliform adaxial epidermis); with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linked with traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries only); forming figures (some forming Is or anchors). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 10. 2n = 30.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 1 species.
Distribution, phytogeography, ecology. Canada, U.S.A. to Argentina.
Species of open habitats. Prairie.
Economic aspects. Significant weed species: S. paniculatus.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia schedonnardi.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • S. paniculatus: Nicora & Rúgolo de Agrasar (1987). • S. paniculatus, abaxial epidermis of leaf blade: this project
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 13th November 2017. delta-intkey.com/grass’.