| # The grass genera of the world |

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

### Leptoloma Chase

From the Greek leptos (thin) and loma (border), alluding to the lemma margins.

~ Digitaria

Habit, vegetative morphology. Perennial; rhizomatous, or caespitose (with a knotty rhizomatous base). Culms 25–80 cm high; herbaceous. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; 2–6 mm wide (rather rigid); not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane; truncate; 1 mm long.

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

Inflorescence. Inflorescence paniculate; deciduous in its entirety; open; with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 2–4 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent (although there may be hair tufts from bases of G2 and L1).

Glumes two (the lower minute and vestigial), or one per spikelet; the G2 relatively large; (when both present), very unequal; (the upper) long relative to the adjacent lemmas; (the upper) often hairy (between the veins); awnless; non-carinate. Lower glume 0 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, reduced. The proximal incomplete florets sterile. The proximal lemmas awnless; 5–7 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas (membranous, often hairy between the veins); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (thinly cartilaginous); striate (minutely rugulose); not becoming indurated; brown in fruit; entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea (hyaline); with a clear germination flap; 3 nerved. Palea present; relatively long; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved. Lodicules present; 2; joined, or free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls. Microhairs present; panicoid-type; (51–)60–66(–75) microns long; 3.6–4.5(–5.4) microns wide at the septum. Microhair total length/width at septum 11.3–18.3. Microhair apical cells (16.5–)22.5–31.5(–39) microns long. Microhair apical cell/total length ratio 0.32–0.52. Stomata common; 25.5–28.5 microns long. Subsidiaries parallel-sided, dome-shaped, and triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapped by the interstomatals (mostly, but a few more or less flush). Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly dumb-bell shaped (some with points); sharp-pointed, or not sharp-pointed (some dumb-bells have points).

Transverse section of leaf blade, physiology. C4; XyMS–. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (constituting most of epidermis). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Tissues of the culm bases with abundant starch.

Cytology. 2n = 72, or 36, or 70 (mostly 72).

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): cf. Panicoideae; Panicodae; Paniceae (?); cf. Anthephorinae (?). 1 species (L. cognatum).

Distribution, phytogeography, ecology. North America.

Rusts and smuts. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma. Ustilaginaceae — Sorosporium.

References, etc. Leaf anatomical: studied by us.

Special comments. Fruit data wanting.

Illustrations. • Leptoloma cognatum: Britton (1913), Ill. Flora of Northern U.S.A., 1.

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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