| # The grass genera of the world |

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

### Monanthochloë Engelm.

From the Greek monos (single), anthos (flower) and chloë (grass), re unisexual flowers.

~ Distichlis

Including Halochloa Griseb., Solenophyllum Baillon

Habit, vegetative morphology. ‘Ericoid’ perennial; rhizomatous and stoloniferous (decumbent, mat-forming). Culms 5–20 cm high; herbaceous; branched above. Leaves not basally aggregated; conspicuously distichous; non-auriculate; without auricular setae. Leaf blades linear-lanceolate to lanceolate; narrow; 1–4 mm wide (to 1 cm long); thick, firm, folded or involute; acicular (subulate); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane; minute. Contra-ligule absent.

Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality (on the same plant); female-only, or male-only. Plants outbreeding.

Inflorescence. Inflorescence reduced to a single spikelet; inconspicuous, the spikelets borne singly, more or less concealed by leaf sheaths; spatheate, or espatheate (depending on interpretation); a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs (depending on interpretation).

Female-sterile spikelets. Male spikelets without glumes, with 2–5 three-stamened florets and incomplete distal florets. The male spikelets without glumes; with proximal incomplete florets; 2–5 floreted. Male florets 3 staminate.

Female-fertile spikelets. Spikelets unconventional (being without glumes); 8–10 mm long; compressed laterally to not noticeably compressed; disarticulating only tardily, at the lowest rachilla node; not disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes absent. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless.

Female-fertile florets 2–5. Lemmas convolute, oblong-lanceolate, leathery or leaflike in texture; not becoming indurated; entire; pointed; awnless; hairless; non-carinate (rounded on the back); perhaps with a germination flap - see illustration by Nicora and de Agrasar (1987); 9 nerved. Palea present; relatively long; convolute around the flower; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma (leathery); 2-nerved (narrow); 2-keeled. Palea keels winged (to embrace the floret above); ciliate. Lodicules absent. Stamens 0 (three staminodes). Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; ellipsoid. Hilum short. Pericarp fused. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae seemingly consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell. Intercostal zones seemingly without typical long-cells (not observable in detail, being obscured by large papillae and prickles). Microhairs present; chloridoid-type (overarched by semicircles of prickles). Stomata common (but largely obscured). Prickles abundant. Costal short-cells predominantly paired (in places), or neither distinctly grouped into long rows nor predominantly paired (then solitary). Costal silica bodies present throughout the costal zones; rounded (mostly, but mostly more or less vertically elongated), or saddle shaped (few); not sharp-pointed.

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

C4; XyMS+. PCR sheath outlines seemingly even (in the poor material seen). PCR sheaths of the primary vascular bundles complete. PCR sheath extensions seemingly absent. PCR cell chloroplasts centripetal. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size (except for the lower one over the midrib). Midrib conspicuous (in lacking an adaxial rib, and having no adaxial strand); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in the furrows); seemingly exclusively in simple fans (these quite small). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles (the bundles other than that of the midrib all with massive adaxial strands and abaxial strands or girders). The lamina margins with fibres.

Cytology. Chromosome base number, x = 10. 2n = 40.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Monanthochloinae. 3 species.

Distribution, phytogeography, ecology. America, West Indies.

Helophytic; species of open habitats; halophytic. Inland salt pans.

Rusts and smuts. Rusts — Puccinia.

References, etc. Leaf anatomical: studied by us - M. littoralis Engelm.

Illustrations. • Monanthochloe acerosa: Nicora & Rúgolo de Agrasar (1987). • Monanthochloe littoralis: Hitchcock (1936), W.I. Grasses.. • Monanthochloe littoralis, abaxial epidermis of leaf blade: this project. • Monanthochloe littoralis, Leaf blade TS: 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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