The grass genera of the world
~ Muhlenbergia sensu lato (M. biloba Hitchc.)
Habit, vegetative morphology. Annual; caespitose. Culms 9–35 cm high; herbaceous; unbranched above. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate; without auricular setae. Sheaths keeled, often striate, longer than the internodes. Leaf blades linear; narrow; 0.6–1.4 mm wide (1–7 cm long); flat, or rolled (involute); without abaxial multicellular glands; without cross venation; persistent. Ligule an unfringed membrane; not truncate (apex acute or rounded, often irregularly toothed); 1.5–3.4 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets hermaphrodite. Plants without hidden cleistogenes.
Inflorescence. Inflorescence paniculate; open; espatheate; not comprising partial inflorescences and foliar organs. Spikelets solitary; not secund; pedicellate; imbricate.
Female-fertile spikelets. Spikelets about 4–4.5 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret (seemingly, from the description and illustrations seen). Hairy callus present. Callus short.
Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; hairy (loosely pilose to villous, especially below); without conspicuous tufts or rows of hairs; pointed; awnless; similar. Lower glume faintly 1 nerved. Upper glume faintly 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas not becoming indurated; incised; 2 lobed (the lobes rounded to obtuse); deeply cleft; awned. Awns 1; median; from a sinus; non-geniculate; flexuous (to crisp-curled); hairless (scabrous); much longer than the body of the lemma; entered by one vein. Lemmas hairy (tawny-villous below); without a germination flap; 3 nerved. Palea present; relatively long (about as long as the lemma, hairy below); entire (obtuse); awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Palea keels wingless; hairy. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 1.2–2.3 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small (about 1.8 mm long); olive-brown; fusiform; not noticeably compressed. Hilum short. Pericarp fused. Embryo large.
Abaxial leaf blade epidermis. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 27–30 microns long. Microhair total length/width at septum 3.5. Microhair apical cell/total length ratio 0.25. Stomata common. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; tall-and-narrow (to squarish).
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines probably even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Midrib conspicuous (via a bulbous abaxial keel); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups to not present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (the penetrating groups contributing to the colourless columns). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres (and very large).
Cytology. Chromosome base number, x = 8. 2n = 16.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 1 species (B. mexicana = Muhlenbergia biloba Hitchc.).
Distribution, phytogeography, ecology. Mexico.
Mesophytic, or xerophytic; glycophytic. In shallow, sandy soils in coniferous woodland, at 2000–2300 m.
References, etc. Morphological/taxonomic: Peterson 1989. Leaf anatomical: photo of mid-blade ts, Peterson et al. 1989; Van den Borre 1994.
Illustrations. • B. mexicana: Lamson-Scribner, True Grasses (1890).. • B. mexicana: Beal (1896), Grasses of N. America 2
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: 11th December 2017. delta-intkey.com/grass’.