| # The grass genera of the world |

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

### Tripsacum L.

From the Greek tri (three) and psakas (small pieces), re breaking up of spikes into (at least) three pieces.

Including Dactylodes Kuntze, Digitaria Adans.

Habit, vegetative morphology. Perennial; forming clumps, from thick knotty rhizomes. Culms 70–400 cm high. Leaves not basally aggregated; non-auriculate. Leaf blades broad, or narrow; flat. Ligule an unfringed membrane to a fringed membrane; short.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets segregated, in different parts of the same inflorescence branch. The spikelets overtly heteromorphic. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence of spicate main branches (terminal and axillary inflorescences of 1–5 racemes, the male spikelets distal to the females on the same rachis); open; digitate, or non-digitate (when unbranched), or subdigitate. Primary inflorescence branches 1–5. Rachides hollowed (in association with the female spikelets). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikelike; with substantial rachides (the female part becoming bony); disarticulating; disarticulating at the joints (in the lower, female part - the male section falling whole). ‘Articles’ non-linear (the female spikelets sunken in the hollows). Spikelets solitary (female spikelets, sometimes accompanied by a rudiment), or paired (males); secund (above: the male spikelets on one side of rachis), or not secund (below: female spikelets opposite); sessile (female), or sessile and pedicellate (male); consistently in ‘long-and-short’ combinations (male), or not in distinct ‘long-and-short’ combinations (female). The ‘shorter’ spikelets female-only, or male-only. The ‘longer’ spikelets male-only.

Female-sterile spikelets. Male spikelets 5–12 mm long, with 2 membranous glumes and 2 florets. The male spikelets with glumes (two); 2 floreted.

Female-fertile spikelets. Spikelets morphologically ‘conventional’ (but the inner parts hyaline); 5–10 mm long; abaxial (?); compressed laterally, or not noticeably compressed, or compressed dorsiventrally (?); falling with the glumes (and the joint). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal (indurate, fused with the rachis); long relative to the adjacent lemmas (enclosing the female spikelets); dorsiventral to the rachis; hairless; awnless; non-carinate. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate, or epaleate; sterile. The proximal lemmas awnless; 0 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; awnless; hairless; non-carinate; without a germination flap; 0 nerved. Palea present (hyaline); awnless, without apical setae; not indurated (hyaline). Lodicules absent. Stamens 0. Ovary apically glabrous. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Hilum short. Embryo large. Endosperm hard; without lipid. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type (but often balanoform and blunt tipped); 49–78 microns long (T. dactyloides), or 81–90 microns long (T. laxum); 12–13.5 microns wide at the septum (in T. laxum). Microhair total length/width at septum 6.2–7.5 (laxum). Microhair apical cells 25–45 microns long (T. dactyloides), or 55–66 microns long (T. laxum). Microhair apical cell/total length ratio 0.54 (T. dactyloides), or 0.69–0.73 (laxum). Stomata common; 57–60 microns long. Subsidiaries dome-shaped to triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Intercostal silica bodies cross-shaped, or crescentic, or vertically elongated-nodular. Costal zones with short-cells. Costal short-cells conspicuously in long rows (in places), or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies tall-and-narrow (few), or ‘panicoid-type’; cross shaped to dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR cell chloroplasts with reduced grana. Mesophyll with non-radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous (keeled); having a conventional arc of bundles (a large median, and a few to many small laterals); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans (sometimes the groups large celled - Zea-type). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with all but the smaller bundles).

Phytochemistry. Leaves containing flavonoid sulphates (1 species), or without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 9. 2n = 36, 72, 90, and 108. 4, 8, 10, and 12 ploid. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Maydeae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Tripsacinae. About 12 species.

Distribution, phytogeography, ecology. Warm America.

Commonly adventive. Helophytic, or mesophytic; shade species and species of open habitats. Open woodland and damp places.

Economic aspects. Significant weed species: T. laxum. Cultivated fodder: several, notably T. andersonii (Guatemala), T. dactyloides, T. laxum.

Hybrids. Intergeneric hybrids with Zea.

Rusts and smuts. Rusts — Physopella and Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - T. laxum Nash.

Illustrations. • Tripsacum dactyloides: Lamson-Scribner (1897), American Grasses. • T. dactyloides: Nicora & Rúgolo de Agrasar (1987). • Tripsacum laxum, abaxial epidermis of leaf blade: 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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