| # The grass genera of the world |

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

### Steirachne Ekman

Habit, vegetative morphology. Perennial; caespitose. Culms 120 cm high; herbaceous; unbranched above. Culm nodes glabrous. Young shoots intravaginal. Leaves non-auriculate. Leaf blades linear (acuminate, setaceous-tipped); narrow; 0.5–2 mm wide; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane, or a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants with hidden cleistogenes. The hidden cleistogenes in the leaf sheaths.

Inflorescence. Inflorescence paniculate; open (compound, the primary branches spiralled); with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 7–11 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with distinctly elongated rachilla internodes between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present. Callus short.

Glumes present; two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; pointed (acute); awnless; carinate; similar (chaffy). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets several; merely underdeveloped (some larger than the perfect florets, but not conspicuously different in shape, by contrast with Ectrosia).

Female-fertile florets 7–8. Lemmas lanceolate-ovate; similar in texture to the glumes (membranous); not becoming indurated; entire; pointed (very acute); mucronate to awned (acuminate-aristate). Awns 1; median; apical; non-geniculate; hairless; much shorter than the body of the lemma. Lemmas hairless; glabrous; carinate (save at the broadly rounded base); without a germination flap; 3 nerved, or 5 nerved (the laterals not excurrent). Palea present; relatively long; apically notched; awnless, without apical setae, or with apical setae (via slightly excurrent nerves); not indurated (membranous); 2-nerved; 2-keeled. Palea keels winged (sulcate and 2-winged); serrate-scabrid. Lodicules present; 2; free (minute); fleshy; glabrous. Stamens 2; with free filaments (short). Anthers 0.8 mm long; not penicillate (greyish); without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

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 (rather thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs present; elongated; clearly two-celled; panicoid-type (but distal cells quite broad). Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs 36–39 microns long. Microhair basal cells 15 microns long. Microhairs 8.4–9.3 microns wide at the septum. Microhair total length/width at septum 3.9–4.6. Microhair apical cells 19.5–24 microns long. Microhair apical cell/total length ratio 0.54–0.67. Stomata common; 24–30 microns long. Subsidiaries low dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent. Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; saddle shaped, tall-and-narrow, crescentic, and oryzoid (but predominantly broad to narrow saddles); not sharp-pointed.

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

C4; XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present. Maximum number of extension cells 3–4. Leaf blade with distinct, prominent adaxial ribs (round-topped). Midrib not readily distinguishable (a somewhat larger bundle and rib); with one bundle only. Bulliforms present in discrete, regular adaxial groups (in every adaxial groove); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (nearly all the bundles). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

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

Distribution, phytogeography, ecology. Brazil.

Species of open habitats.

References, etc. Morphological/taxonomic: Ekman 1911. Leaf anatomical: studied by us - S. diandra Ekman.

Illustrations. • Steirachne diandra, as Eragrostis barbata: Fl. Brasiliensis 2 (1878). • Steirachne diandra, 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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