The grass genera of the world
~ Muhlenbergia sensu lato
Habit, vegetative morphology. Annual (B. shepherdi), or perennial (B. tricholepis); caespitose, or decumbent. Culms (16–)20–60 cm high; herbaceous; branched above (B. shepherdi), or unbranched above. Culm nodes mostly hidden by leaf sheaths; glabrous. Culm internodes solid to hollow. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate; without auricular setae. Leaf blades linear; narrow; to 2 mm wide; setaceous (B. ticholepis), or not setaceous; flat, or rolled (involute, conspicuously so in B. tricholepis); without abaxial multicellular glands; without cross venation; persistent. Ligule an unfringed membrane; not truncate (rounded, entire to lacerate); 0.7–3 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (to somewhat contracted, greyish, elliptic, 5–20 cm long); with capillary branchlets (the pedicels wiry, flexuous); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate (the long slender pedicels distended towards the tip).
Female-fertile spikelets. Spikelets (1.4–)1.8–3(–4) mm long; dark brown or purplish; slightly compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent (callus glabrous). Callus short; blunt (truncate).
Glumes two; relatively large; very unequal to more or less equal (G1 2/3 to 3/4 the length of G2); about equalling the spikelets; (the upper) long relative to the adjacent lemmas; hairless (glabrous, glossy); glabrous; not pointed (rounded to erose); awnless; non-carinate; similar (greyish green, delicately membranous, broadly ovate to lanceolate). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas lanceolate, greyish green; similar in texture to the glumes to decidedly firmer than the glumes (hyaline to thinly membranous); smooth; not becoming indurated; entire (or erose); pointed to blunt; awnless, or mucronate (rarely); hairy (with long, silky hairs over the lower 2/3 of the midnerve and margins); slightly carinate; without a germination flap; 3 nerved. Palea present; relatively long; entire (pointed); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (but the nerves are much closer than is usual in paleas); keel-less. Palea back densely silky villous hairy (between the nerves below). Lodicules present; 2; free; fleshy (fairly); glabrous; not or scarcely vascularized. Stamens 3; with free filaments (these short). Anthers 0.8–2.1 mm long (relatively long); not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases; free. Stigmas 2; apparently green.
Fruit, embryo and seedling. Fruit brownish; fusiform, or ellipsoid; glabrous. Hilum short. Pericarp fused. Embryo large. Endosperm hard. 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 (despite the lack or scarcity of stomata in B. tricholepis). Papillae present (in B. shepherdi), or absent (in B. tricholepis); intercostal. Intercostal papillae not over-arching the stomata; consisting of one oblique swelling per cell (often adjacent to a stoma). Long-cells markedly different in shape costally and intercostally (costals narrower); of similar wall thickness costally and intercostally (thick walled). Intercostal zones with typical long-cells (all epidermal cells large). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs 30–31.5(–34.5) microns long; (10.5–)11.4–12.3(–14.4) microns wide at the septum. Microhair total length/width at septum 2–2.8. Microhair apical cells (10.5–)12–13.5(–15.6) microns long. Microhair apical cell/total length ratio 0.34–0.5. Stomata common (in B. shepherdi), or absent or very rare (B. tricholepis); 18–22.5 microns long (in B. tricholepis). Subsidiaries non-papillate; (B. shepherdi dome-shaped. Intercostal short-cells common (in B. tricholepis), or absent or very rare (B. shepherdi); in B. tricholepis in cork/silica-cell pairs (also solitary and in short rows); silicified. Intercostal silica bodies imperfectly developed. Rows of costal prickles present. Costal short-cells conspicuously in long rows (interrupted by prickles). Costal silica bodies present in alternate cell files of the costal zones; relatively broad to narrow saddle shaped (sometimes approaching tall-and-narrow and crescentic).
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present, or absent. Maximum number of extension cells when present, 1, or 2. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (between all bundles; very wide). Leaf blade with distinct, prominent adaxial ribs (only, in B. tricholepis), or nodular in section (B. shepherdi); with the ribs more or less constant in size. Midrib conspicuous (with a somewhat larger bundle plus sclerenchyma and rib); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these conrtibuting to the colourless intercostal columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (primaries with abaxial girders and adaxial strands (the PCA tissue encircling the top of each bundle); small bundles with strands only). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 8. 2n = 16. 2 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 2 species.
Distribution, phytogeography, ecology. Southwest U.S.A., Mexico.
Xerophytic; species of open habitats; glycophytic. Dry upland coniferous forest.
References, etc. Morphological/taxonomic: Peterson and Annable 1990. Leaf anatomical: this project, supplemented from Peterson and Annable 1990.
Illustrations. • B. tricholepis: Hitchcock and Chase (1950). • B. tricholepis, abaxial epidermis of leaf blade: this project. • B. tricholepis, TS 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’.