| # The grass genera of the world |

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

### Leptothrium Kunth

Including Latipes Kunth

Habit, vegetative morphology. Perennial; caespitose. Culms 10–75 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Plants unarmed. Leaves not basally aggregated; non-auriculate. Sheath margins free. Leaf blades narrow; 1–2 mm wide (to 8 cm long); flat, or rolled; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs. Contra-ligule absent.

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

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (an elongated false raceme), or a single raceme (the ‘clusters’ each reduced to one peduncled spikelet in L. rigidum); contracted (the ‘pedicels’ (peduncles) flattened, cuneate, fringed, the rachis long and slender); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (i.e., the panicle branches reduced to the pedicel-like peduncle and one or two spikelets); disarticulating; falling entire (the peduncles falling). Spikelets solitary (L. rigidum), or paired (L. senegalensis); not secund; sessile.

Female-fertile spikelets. Spikelets 3–8 mm long; compressed laterally (except for the larger asymmetric spikelet in L. senegalensis); falling with the glumes (and the pedicels); with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large (asymmetric in L. senegalensis); very unequal; (the upper) long relative to the adjacent lemmas (exceeding the lemma); pointed (subulate-acuminate); awnless (subulate, muticate, leathery, shining); with the keel conspicuously winged (in upper part of G2 in L. rigidum), or without a median keel-wing; very dissimilar (G1 of L. rigidum and of one spikelet of the pair in L. senegalensis dorsally flattened, ciliate towards the tip, recurving, more or less free of the rest of the spikelet; G2 shorter, laterally flattened towards the tip, tuberculate-spiny or not). Lower glume tuberculate, or prickly; 1 nerved, or 3–5 nerved. Upper glume 5 nerved; prickly, or not prickly. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; pointed; awnless; hairless; glabrous; carinate; without a germination flap; 1 nerved, or 3 nerved. Palea present; very reduced (and delicate); entire; awnless, without apical setae; nerveless; keel-less. Lodicules present; 2; free; fleshy, or membranous; glabrous; not or scarcely vascularized. Stamens 3. Anthers relatively long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2 mm long); compressed laterally. Hilum short. Pericarp loosely adherent. Embryo large; waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent; when seen, intercostal. Intercostal papillae consisting of one oblique swelling per cell. Long-cells the costal cells longer; of similar wall thickness costally and intercostally (medium thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 21–33 microns long. Microhair basal cells 18 microns long. Microhairs 11.4–13.5 microns wide at the septum. Microhair total length/width at septum 1.7–2.8. Microhair apical cells 7.5–8.4 microns long (L. rigidum), or 9.6–12.6 microns long (L. senegalensis). Microhair apical cell/total length ratio 0.23–0.48. Stomata common; 16.5–18 microns long (L. rigidum), or 21–34.5 microns long (L. senegalensis). Subsidiaries low dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare (very rare in L. senegalensis); in cork/silica-cell pairs (and solitary); silicified. Intercostal silica bodies absent. Costal prickles abundant. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; mostly dumb-bell shaped; not sharp-pointed.

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

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (round-topped). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (the groups large, between each bundle pair); in simple fans (the large median cells deeply penetrating). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with most bundles); forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 10.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Gymnopogoninae. 2 species.

Distribution, phytogeography, ecology. Caribbean & Senegal to Pakistan.

Xerophytic; halophytic, or glycophytic. Dry bushland, open seashore, sandy thickets.

Economic aspects. Cultivated fodder: L. senegalense used for re-seeding denuded ground. Important native pasture species: L. senegalense.

References, etc. Leaf anatomical: studied by us - L. senegalense (formerly Latipes), L. rigidum Kunth.

Illustrations. • Leptothrium senegalense, as Latipes: Kunth (1835). • Leptathrium rigidum: Hitchcock (1936). • Leptothrium senegalense: Rose Innes, Ghana Grasses (1977).

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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