| # The grass genera of the world |

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

### Pentarrhaphis Kunth

~ Bouteloua sensu lato

Including Polyschistis Presl, Strombodurus Steud.

Habit, vegetative morphology. Perennial; caespitose. Culms 30–60 cm high; herbaceous; unbranched above (slender). Culm nodes glabrous. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate. Leaf blades linear; narrow; to 2 mm wide; setaceous (at the tips); without cross venation; persistent. Ligule a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality (P. polymorpha); hermaphrodite, or hermaphrodite and sterile (2-spikeleted racemelets, P. polymorpha having both well developed, the others with one well developed and the other reduced to its awnlike glumes); all in heterogamous combinations.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the clusters cuneate, bristly). Inflorescence axes not ending in spikelets (with a forked rachis prolongation). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (to the clusters, which in two species are reduced to a single fertile spikelet and a vestigial one reduced to its awns, the rachis terminating in a forked bristle (5 bristles in total); in P. polymorpha, both spikelets are well developed); disarticulating; falling entire (i.e., the reduced glomerules falling). Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches, or with ‘involucres’ of ‘bristles’. The ‘bristles’ when present, deciduous with the spikelets. Spikelets not secund; shortly pedicellate.

Female-fertile spikelets. Spikelets more or less morphologically ‘conventional’ (there is scope to argue that the structure regarded here as the ‘fertile spikelet’ is really two spikelets, but this would necessitate arguing that the ‘upper one’ has no glume); about 4 mm long; compressed dorsiventrally; falling with the glumes (and with the associated rudiments); not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (beneath the sterile floret, glabrous above it); the rachilla extension with incomplete florets.

Glumes present; two (the G1 represented by one of the bristles, hard to recognise as such); shorter than the adjacent lemmas; (the upper) hairy (having long white hairs over the lower half); apically two-lobed; awned (the lower reduced to an awn, the upper with a 1.5 mm awn from a sinus); (the upper) non-carinate (rounded, hyaline); very dissimilar (the lower a hirsute bristle, the upper acicular to lanceolate). Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1 (male or sterile).

Female-fertile florets 1. Lemmas membranous or cartilaginous; not becoming indurated; incised; 4 lobed (two large lateral lobes, and the central awn flanked by two teeth); deeply cleft (three cleft, laterally to halfway and shallowly in association with the central awn); awned. Awns 3 (all recurved-spreading); median and lateral; the median similar in form to the laterals; from a sinus (from between the central teeth); non-geniculate; recurving; hairless (scabrid); about as long as the body of the lemma (all three awns of similar lengths). The lateral awns about equalling the median (from the inner edges of the outer lobes). Lemmas hairy; non-carinate (rounded); without a germination flap; 3 nerved. Palea present; relatively long; apically notched (rather deeply); awnless, without apical setae, or with apical setae (via excurrent nerves); not indurated (hyaline, glabrous); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3; with free filaments (these short). Anthers long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit ellipsoid.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs present; elongated; clearly two-celled; panicoid-type to chloridoid-type (the apical cell thin-walled, often collapsed); (34.5–)36–39(–42) microns long; (6–)7.5–8.4 microns wide at the septum. Microhair total length/width at septum 4.3–5.8. Microhair apical cells (13.5–)14.4–18(–19.5) microns long. Microhair apical cell/total length ratio 0.39–0.43. Stomata common; (27–)28.5–30(–33) microns long. Subsidiaries dome-shaped and triangular (mostly dome-shaped). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic and saddle shaped (small). Costal short-cells conspicuously in long rows. Costal silica bodies saddle shaped (larger towards the blade margins); not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS+ (the sheath cells thick-walled). PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells (but not in the marginal flanges). Leaf blade adaxially flat (with expanded leaf margins, each bearing two large bundles and a small one on the outside). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the large marginal bundles, the rest mostly having only scanty adaxial and abaxial strands); forming ‘figures’ (the marginal bundles). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Boutelouinae (as a synonym of Bouteloua). 3 species.

Distribution, phytogeography, ecology. Mexico to Columbia.

Species of open habitats. Dry scrub.

References, etc. Leaf anatomical: studied by us - P. scabra H.B.K.

Special comments. Fruit data wanting.

Illustrations. • Pentarrhaphis scabra: Kunth, Nova Genera et Species Plantarum (1815).

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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