Grass Genera of the World

L. Watson and M. J. Dallwitz

Muhlenbergia Schreber

Named for G.H.E. Muhlenberg.

Including Acroxis Steud., Anthipsimus Raf., Calycodon Nutt, Clomena P. Beauv., Crypsinna Fourn., Dactylogramma Link, Dilepyrum Michaux, Epicampes Presl, Lepyroxis Fourn., Podosemum Desv., Sericrostis Raf., Tosagris P. Beauv., Trichochloa DC., Vaseya Thurber

Excluding Chaboissaea, Bealia, Hubbardochloa

Habit, vegetative morphology. Annual (rarely), or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 2–100 cm high, or 100–200 cm high (rarely); herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; setaceous, or not setaceous; flat, or rolled; without abaxial multicellular glands; without cross venation; persistent; rolled in bud; an unfringed membrane (e.g., in Section Epicampes), or a fringed membrane.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants exposed-cleistogamous, or chasmogamous; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths (sometimes very modified).

Inflorescence. Inflorescence paniculate; open, or contracted (then narrow, sometimes spikelike); with capillary branchlets, or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 1.7–3.5 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret (nearly always, the upper floret usually absent, but when present usually fertile). Hairy callus present (very short). Callus short.

Glumes two (though rarely the G1 is obsolete); very unequal to more or less equal; shorter than the spikelets to about equalling the spikelets (rarely longer); shorter than the adjacent lemmas (usually), or long relative to the adjacent lemmas; obtuse to acuminate; awned, or awnless; carinate, or non-carinate; very dissimilar, or similar. Lower glume 0–2 nerved. Upper glume 0–3 nerved. Spikelets nearly always with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1, or 2 (rarely). Lemmas similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated (firmly membranous); entire, or incised; when incised 2 lobed (minutely bifid); not deeply cleft (at the most shortly bidentate); mucronate, or awned. Awns 1; from a sinus, or dorsal, or apical; when dorsal, from near the top; non-geniculate; straight, or flexuous; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairy (rarely long-pilose, usually minutely pilose), or hairless; non-carinate; without a germination flap; 3 nerved. Palea present; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 0.3–2.7 mm long; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2; red pigmented, or brown.

Fruit, embryo and seedling. Fruit free from both lemma and palea (but the lemma tightly enclosing the grain); small; fusiform, or ellipsoid; not noticeably compressed. Hilum short. Pericarp fused. Embryo large. Endosperm hard; without lipid. Embryo 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; consisting of one oblique swelling per cell. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (16.5–)18–50(–52.5) microns long. Microhair basal cells 36 microns long. Microhairs (4.5–)5.4–12(–12.3) microns wide at the septum. Microhair total length/width at septum 1.5–11.2. Microhair apical cells (3–)4.5–10.5(–12) microns long. Microhair apical cell/total length ratio 0.14–0.33. Stomata common; 16.5–22.5 microns long. Subsidiaries low to high dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped, or ‘panicoid-type’ (sometimes pointed); when panicoid type, cross shaped to dumb-bell shaped; sharp-pointed, or not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; biochemical type PCK (1 species); XyMS+. PCR sheath outlines uneven (e.g. M. diversiglumis, M. ciliata), or even (e.g. M. breviculmis, M. pusilla, M. ramulosa). 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; centrifugal/peripheral (e.g. M. microsperma, and seemingly M. ciliata and M. diversiglumis), or centripetal (e.g. M. ramulosa). Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma (rarely); traversed by columns of colourless mesophyll cells (e.g. M. confusa, M. breviculmis, M. pusilla), or not traversed by colourless columns (e.g. M. ciliata, M. diversiglumis, M. microsperma). Leaf blade ‘nodular’ in section, or adaxially flat; when present, with the ribs more or less constant in size (low). Midrib conspicuous; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (predominant in e.g. M. diversiglumis, M. microsperma), or associated with colourless mesophyll cells to form deeply-penetrating fans (often linked with traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent (e.g. M. confusa); forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Tissues of the culm bases with abundant starch.

Cytology. Chromosome base number, x = 10. 2n = 20, 40, 42, and 60. 2 and 4 ploid. Chromosomes ‘medium sized’.

Taxonomy. Chloridoideae; main chloridoid assemblage.

Distribution, ecology, phytogeography. 160 species; Himalayas to Japan, North America to Andes. Commonly adventive. Mesophytic to xerophytic; species of open habitats. Diverse habitats, commonly in open grassland, important in arid and semi-arid regions.

Holarctic, Paleotropical, and Neotropical. Boreal, Tethyan, and Madrean. Indomalesian. Eastern Asian, Atlantic North American, and Rocky Mountains. Irano-Turanian. Indian, Indo-Chinese, Malesian, and Papuan. Caribbean, Pampas, and Andean. Canadian-Appalachian, Southern Atlantic North American, and Central Grasslands.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia striiformis, and Puccinia schedonnardi. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma and Tilletia. Ustilaginaceae — Sphacelotheca and Ustilago.

Economic importance. Significant weed species: M. schreberi. Important native pasture species: M. emersleyi, M. montana, M. pauciflora, M. wrightii.

References, etc. Morphological/taxonomic: Soderstrom 1967. Leaf anatomical: Metcalfe 1960; this project; and for illustrations of leaf transverse sections showing photosynthetic pathway-related features, see Peterson et al. 1989.

Illustrations. • Abaxial epidermis of leaf blade. Muhlenbergia arisanensis. • Transverse section of leaf blade, electron micrograph. Muhlenbergia montana. C4 type NAD-ME. • Transverse section of leaf blade, electron micrograph. Muhlenbergia montana. C4 type NAD-ME.

Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).