| # The grass genera of the world |

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

### Monium Stapf

~ Anadelphia

Habit, vegetative morphology. Annual, or perennial; when perennial, caespitose. Culms 20–90 cm high; herbaceous; branched above, or unbranched above. Culm nodes exposed; glabrous. Culm leaves present. Leaves not basally aggregated. The sheaths with a strong median nerve. Leaf blades linear; narrow; 0.25–3 mm wide; setaceous, or not setaceous; flat; without cross venation; persistent. Ligule an unfringed membrane; truncate to not truncate; 1–2 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (but the pedicelled spikelet may be so reduced as to be hidden among the callus hairs of the fertile spikelet); hermaphrodite and sterile, or hermaphrodite and male-only; overtly heteromorphic (the pedicelled spikelet much reduced); all in heterogamous combinations. Plants exposed-cleistogamous (? - the greatly reduced ‘raceme’ inclosed within its spathe), or chasmogamous (?).

Inflorescence. Inflorescence paniculate; open; with capillary branchlets to without capillary branchlets; spatheate (and spatheolate); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes very much reduced (the ‘raceme’ shorter than the spatheole, bearing only the one fertile spikelet and its pedicelled satellite); the spikelet-bearing axes with only one spikelet-bearing ‘article’; solitary; disarticulating; disarticulating at the joints (i.e., each ‘raceme’ disarticulating at the only joint). ‘Articles’ without a basal callus-knob; disarticulating obliquely (the single ‘joint’ obliquely articulated on the somewhat swollen peduncle tip). Spikelets paired (no triplets); sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile (and often reduced to a vestigial pedicel).

Female-sterile spikelets. Pedicellate spikelets often reduced to a minute pedicel, which may be concealed among the callus hairs. When developed, acuminate with a glabrous callus.

Female-fertile spikelets. Spikelets 5–10 mm long; not noticeably compressed to compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long; pointed.

Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (exceeding them); free; hairless; glabrous; without conspicuous tufts or rows of hairs; awned (the G2 only, or sometimes the G1 two-awned), or awnless (the G2 then subulate-tipped or apiculate); non-carinate; very dissimilar (both leathery, the G1 apically truncate to bidentate and round-backed, the G2 subulate or apiculate at tip, naviculate). Lower glume not two-keeled (except towards the tip); convex on the back; not pitted; relatively smooth; 5 nerved, or 7 nerved (with a median). Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless (pointed to bilobed); 0 nerved, or 2 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas somewhat displaced; less firm than the glumes (hyaline); not becoming indurated; incised; 2 lobed; deeply cleft to not deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairless, or hairy; much longer than the body of the lemma (5–16 cm long). Awn bases twisted; not flattened. Lemmas hairy, or hairless; glabrous; non-carinate; without a germination flap; 1 nerved. Palea absent (according to Jacques-Félix 1962, and in the material seen - by contrast with ‘Anadelphia scyphofera’). Lodicules present; 2; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles basally fused; joined below. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid; not noticeably compressed (more or less cylindrical); glabrous. Embryo large. Endosperm hard.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal (but not over the midrib). Intercostal papillae not over-arching the stomata; consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell (large, thick walled). Mid-intercostal long-cells basically rectangular; having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 31–36 microns long; 5.1–5.4 microns wide at the septum. Microhair total length/width at septum 6.1–6.7. Microhair apical cells 19–24 microns long. Microhair apical cell/total length ratio 0.59–0.67. Stomata common; 24–26 microns long. Subsidiaries non-papillate; triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells seemingly absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed (in places, but extensively obscured by papillae); ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. Leaf blade with distinct, prominent adaxial ribs (the ribs very low). Midrib conspicuous; having a conventional arc of bundles (one median, with smaller laterals); with colourless mesophyll adaxially (e.g. M. macrochaeta), or without colourless mesophyll adaxially (but with the overlying adaxial epidermis bulliform). Bulliforms present in discrete, regular adaxial groups (the groups wide), or not present in discrete, regular adaxial groups (if the same configuration is interpreted as ‘epidermis extensively bulliform’); in simple fans; associating with colourless mesophyll cells to form arches over small vascular bundles (seemingly, in places, in M. funerea), or nowhere involved in bulliform-plus-colourless mesophyll arches. All the vascular bundles accompanied by sclerenchyma (in M. funerea), or many of the smallest vascular bundles unaccompanied by sclerenchyma (in M. trichaeta). Combined sclerenchyma girders present (with all the primaries and some of the smaller bundles, other small bundles with small strands only); forming ‘figures’ (the main bundles). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): cf. Panicoideae (as a synonym?); Andropogonodae; Andropogoneae; cf. Anthistiriinae. 7 species.

Distribution, phytogeography, ecology. Tropical West Africa.

References, etc. Leaf anatomical: studied by us - M. funereum Jac-Fél., M. macrochaetum Stapf, M. trichaetum Reznik.

Special comments. See comment under Anadelphia regarding unsatisfactory taxonomy involving Monium, Anadelphia and Pobeguinea.

Illustrations. • Monium macrochaetum: Hook. Ic. Pl. 31 (1922). • Monium trepidarium (as M. congestum): Jacques-Félix, 1962. • Monium funereum, 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: 15th June 2025. delta-intkey.com’.

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