| # The grass genera of the world |

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

### Steinchisma Raf.

~ Panicum (Subgenus Steinchisma, including (e.g.) Panicum hians = P. milioides)

Excluding Cliffordiochloa

Habit, vegetative morphology. Perennial. Culms herbaceous; sparsely to amply branched above, or unbranched above. The branching simple. Leaf blades not pseudopetiolate; without cross venation.

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

Inflorescence. Inflorescence paniculate; more or less contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; not two-ranked; pedicellate. Pedicel apices cupuliform.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes; with conventional internode spacings. The upper floret not stipitate. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal (the lower short); (the upper) long relative to the adjacent lemmas (almost as long as the spikelet); without conspicuous tufts or rows of hairs; awnless; non-carinate. Lower glume shorter than the lowest lemma. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed; becoming conspicuously hardened and enlarged laterally. The proximal lemmas awnless; 3 nerved; less firm than the female-fertile lemmas.

Female-fertile florets 1. Lemmas not saccate; decidedly firmer than the glumes; smooth; becoming indurated; entire; awnless; non-carinate; having the margins inrolled against the palea; with a clear germination flap. Palea present; awnless, without apical setae. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells differing markedly in wall thickness costally and intercostally (the costals thinner walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; of S. hians 54–57 microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 9–10. Microhair apical cells 27–34.5 microns long. Microhair apical cell/total length ratio 0.5–0.65. Stomata common; in S. hians 21–24 microns long. Subsidiaries mostly high dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (mostly ostensibly solitary, but a few obvious pairs); not silicified (in the material of S. hians seen). Small intercostal prickles abundant. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies abundant, ‘panicoid-type’; cross shaped, butterfly shaped, and dumb-bell shaped (short); not sharp-pointed.

Transverse section of leaf blade, physiology. C4 to C3 (intermediate, with C3-like mesophyll layout), or C3 (seemingly C3 in S. laxa and S. stevensianum). The anatomical organization unconventional (in that there are some organelles in the outer sheath). XyMS+. PCR cell chloroplasts centripetal. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section; with the ribs more or less constant in size (round topped). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in all the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the bundles with I’s or ‘anchors’). Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves containing flavonoid sulphates, or without flavonoid sulphates.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Otachyriinae. 8 species.

Distribution, phytogeography, ecology. Southern U.S.A. to Argentina.

Commonly adventive. Mesophytic. Damp grassland.

Economic aspects. Significant weed species: S. hians.

References, etc. Leaf anatomical: studied by us - S. hians (Panicum hians Ell.).

Illustrations. • Steinchisma laxum, as Panicum diandrum: Kunth (1835). • Steinchisma hians: Britton & Brown (1913), Ill. Flora of Northern U.S.A.. • Steinchisma hians, as Panicum: Hitchcock and Chase (1950). • Steinchisma hians, T.S. leaf blade - fluorescence image: 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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