| # The grass genera of the world |

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

### Chaboissaea Fourn.

~ Muhlenbergia sensu lato

Habit, vegetative morphology. Annual, or perennial; caespitose, or decumbent. Culms (3–)5–70(–90) cm high; herbaceous; unbranched above (sometimes freely branched below). Culm nodes exposed; glabrous. Culm internodes hollow. Leaves not basally aggregated; non-auriculate; without auricular setae. Sheaths glabrous, usually shorter than the internodes, sometimes keeled. Leaf blades linear; narrow; 0.7–2.8(–3) mm wide; flat, or rolled (to loosely involute); not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane; somewhat truncate, or not truncate; 1.5–3.2 mm long, or 6–10 mm long (C. ligulata). Contra-ligule absent.

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

Inflorescence. Inflorescence paniculate (terminal, narrow, the branches distant, alternate, subdivided, strongly appressed); open to contracted. Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets pedicellate (the pedicels 0.2–3 mm long); imbricate.

Female-fertile spikelets. Spikelets about 2.5–3.6 mm long; dark grey or lead coloured to greyish yellow; compressed laterally; disarticulating above the glumes; disarticulating between the florets (?). Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal to more or less equal (to ‘subequal’); shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous (scabrous along the midnerve); pointed (acute or acuminate); awned, or awnless (often one or both awn-tipped); similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1–2; merely underdeveloped.

Female-fertile florets 1. Lemmas chartaceous; not becoming indurated; entire, or incised; pointed (acute to acuminate); sometimes minutely 2 lobed; not deeply cleft; awnless to awned. Awns 1; median; from a sinus, or dorsal, or apical (seemingly, from illustrations in Peterson and Annable 1992); if dorsally awned, from near the top; non-geniculate; straight, or flexuous; hairless; much shorter than the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairy (with miute appressed hairs below, along the midnerve and margins); more or less carinate (somewhat compressed-keeled, at least above); without a germination flap; 3 nerved. Palea present; relatively long; apically notched; awnless, without apical setae, or awned (the nerves often produced into two short awns); 2-nerved; 2-keeled. Palea back glabrous. Palea keels wingless. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 0.9–2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; ‘dark gray’.

Fruit, embryo and seedling. Fruit small (1–2.5 mm long); brownish; fusiform. Hilum short (?). Embryo large. Seed endospermic. 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. Papillae present; intercostal. Intercostal papillae consisting of one symmetrical projection per cell. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Stomata common. Subsidiaries dome-shaped. Intercostal short-cells not paired. Macrohairs absent, and prickles restricted to the blade margins. Costal silica bodies present and well developed; present in alternate cell files of the costal zones; saddle shaped.

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

C4; XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only, or interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section. Midrib with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (linked with the traversing columns of colourless cells). Combined sclerenchyma girders present (with primary bundles). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 8. 2n = 16 and 32, or 14, 16, and 18 (C. subbflora). 2 and 4 ploid (C. decumbens being tetraploid).

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 4 species (M. atacamensis Parodi, M. decumbens Swallen, M. ligulata Fourn., M. subbiflora Hitchc.)).

Distribution, phytogeography, ecology. Mexico, Argentina.

Helophytic to mesophytic; species of open habitats; glycophytic. Marshy meadows.

References, etc. Morphological/taxonomic: Peterson, P.M. and Annable, C.R. (1992). A revision of Chaboissaea (Poaceae: Eragrostideae). Madroño 39, 8–30 (from which the above is taken in its entirety). Leaf anatomical: exclusively from description and illustrations in Peterson and Annable 1992.

Illustrations. • Chaboissaea ligulata: Chase, J. Wash. Acad. Sci. 43 (1953).

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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