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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Munroa J. Torr.

Named for William Munro.

Including Hemimunroa Parodi

Habit, vegetative morphology. Prostrate annual; stoloniferous (low, spreading, much-branched, exhibiting long naked internodes, with fascicles of leaves and inflorescences). Culms 5–20 cm high; herbaceous; amply branched above. The branching simple. Culm internodes solid, or hollow. Leaves non-auriculate. The sheaths expanded. Leaf blades short, acuminate, pungent; narrow; flat, or folded, or rolled, or acicular; without abaxial multicellular glands; not pseudopetiolate; without cross venation; persistent. Ligule a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence reduced to a single spikelet, or few spikeleted; paniculate (of terminal, leafy clusters); contracted; capitate. Inflorescence with axes ending in spikelets. Inflorescence spatheate (i.e., the inflorescence leaves with broad sheaths); a complex of ‘partial inflorescences’ and intervening foliar organs (in that the reduced panicles of small spikelet clusters are almost hidden among the fascicles of leaves). Spikelet-bearing axes very much reduced and paniculate (comprising small subsessile clusters of 2–4 spikelets); persistent, or disarticulating (the complete inflorescences deciduous in some species). Spikelets not secund; subsessile.

Female-fertile spikelets. Spikelets 6–8 mm long; compressed dorsiventrally; disarticulating above the glumes, or falling with the glumes (in species where the inflorescence falls entire); not disarticulating between the florets (when the inflorescence is shed), or disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two (lower spikelets), or one per spikelet (upper spikelets); very unequal, or more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; pointed (acute, narrow); awnless. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (the proximal 1–2 florets female or hermaphrodite, those above hermaphrodite, the uppermost reduced or sterile). The distal incomplete florets merely underdeveloped.

Female-fertile florets 2–3 (upper spikelets), or 3–8 (lower spikelets). Lemmas less firm than the glumes to similar in texture to the glumes (lower leathery, upper membranous); not becoming indurated; incised; 4 lobed, or 2 lobed; mucronate, or awned (one or three mucronate or awned, from the nerves between the lobes). Awns when present, 1, or 3; median, or median and lateral; the median from a sinus, or apical; non-geniculate; hairless; much shorter than the body of the lemma (to 2 mm long). Lemmas hairy. The hairs in tufts (from the middle of each margin). Lemmas non-carinate; without a germination flap; 3 nerved. Palea present; relatively long; tightly clasped by the lemma; apically notched; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled. Lodicules present (small), or absent; 2; joined to the palea; membranous. Stamens 2, or 3. Anthers 1–1.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Stigmas 2; white.

Fruit, embryo and seedling. Fruit small; ellipsoid; compressed laterally. Hilum short. Pericarp thin (translucent, oval); 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 absent. Mid-intercostal long-cells rectangular (rather irregularly so, but not fusiform); having markedly sinuous walls (the walls quite thick). Microhairs present; more or less spherical; clearly two-celled; chloridoid-type (of the short basal cell type). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 24(–25.5) microns long. Microhair basal cells 9 microns long. Microhairs 11.4–14.4 microns wide at the septum. Microhair total length/width at septum 1.7–2.2. Microhair apical cells 10.5–15 microns long. Microhair apical cell/total length ratio 0.44–0.63. Stomata common; 24–27 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired; silicified. Intercostal silica bodies imperfectly developed; tall-and-narrow. Costal short-cells conspicuously in long rows (over some veins), or predominantly paired (in places, especially near the leaf margins), or neither distinctly grouped into long rows nor predominantly paired (with some short rows, or the long rows irregularly broken by long ‘short-cells’). Costal silica bodies present throughout the costal zones to present in alternate cell files of the costal zones; ‘panicoid-type’ (mostly), or saddle shaped (common only near the leaf margins); predominantly plump cross shaped and dumb-bell shaped; 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 complete. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section, or adaxially flat. Midrib conspicuous (via its fairly conspicuous rounded keel, and the lack of adaxial sclerenchyma); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (these sometimes deeply penetrating via a large median cell), or associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all bundles save the median); forming ‘figures’ (all but the midrib with massive anchors). Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups; abaxial-hypodermal, the groups isolated (apart from massive marginal sclerenchyma groups, there is a conspicuous group abaxially opposite each bulliform hinge group - i.e. flanking the midrib). The lamina margins with fibres.

Cytology. Chromosome base number, x = 7 and 8. 2n = 14 and 16. 2 ploid.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Scleropogoninae. 5 species.

Distribution, phytogeography, ecology. 1 in the western U.S.A., 4 in the central Andes.

Xerophytic; species of open habitats. Dry plains.

References, etc. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • M. squarrosa: Hook. Ic. Pl. 14 (1880–82). • M. decumbens: Nicora & Rúgolo de Agrasar (1987). • M. squarrosa, 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’.

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