| # The grass genera of the world |

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

### Lamprothyrsus Pilger

From the Greek lampros (splendid) and thyrsos (an ornamental wand), referring to the large silvery inflorescence.

~ Cortaderia

Type species: Type: L. hieronymi (Kuntze) Pilger.

Habit, vegetative morphology. Cortaderia-like perennial; caespitose. Culms 100–230 cm high; herbaceous. Young shoots intravaginal. Leaves not basally aggregated. Leaf blades linear; narrow; rolled (long, involute); without cross venation; disarticulating from the sheaths. Ligule a fringe of hairs.

Reproductive organization. Plants (gyno?) dioecious (males rarer than females); without hermaphrodite florets. The spikelets hermaphrodite and female-only (?), or female-only, or male-only. Plants outbreeding. Apomictic (non-pseudogamous).

Inflorescence. Inflorescence paniculate; open to contracted (large, to 50 cm long, with many spikelets); non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets compressed dorsiventrally; disarticulating above the glumes; disarticulating between the florets (at the bases of the rachilla joints). Rachilla prolonged beyond the uppermost female-fertile floret; hairy (long-villous); the rachilla extension with incomplete florets. Hairy callus present. Callus linear.

Glumes two; very unequal; shorter than the spikelets (1/2–2/3 as long); long relative to the adjacent lemmas (slightly longer); hairless; glabrous; pointed; awned to awnless; similar (hyaline, acuminate to an awn point). Lower glume 0 nerved, or 1 nerved. Upper glume 0 nerved, or 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 4–10. Lemmas hyaline; not becoming indurated; incised; 2 lobed; deeply cleft (into setae almost as long as the awns); awned. Awns 3; median and lateral (the lemma teeth acuminate into long delicate awns); (the median) different in form from the laterals; from a sinus; non-geniculate to geniculate; recurving (flat, spreading from near the scarcely twisted base, flexuous or loosely twisted above). Lemmas hairy (with silvery hairs); non-carinate; 5 nerved. Palea present; relatively long (longer than the body of the lemma); apically notched; awnless, without apical setae; 2-keeled. Palea back hairy (pilose). Palea keels hairy. Lodicules present; 2; free; ciliate, or glabrous. Stamens 0 (3 staminodes). Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Hilum long-linear. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Ovule, embryology. Outer integument covering no more than the chalazal half of the ovule. Inner integument discontinuous distally. Synergids haustorial (strongly developed).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or lacking (L. peruvianus). Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls (rather thick). Microhairs present, or absent (L. peruvianus); panicoid-type. Stomata absent or very rare (L. peruvianus), or common (L. hieronymi). Subsidiaries low dome-shaped, or triangular (slightly). Intercostal short-cells common. Costal short-cells conspicuously in long rows (L. hieronymi), or neither distinctly grouped into long rows nor predominantly paired (short-cells regularly spaced, solitary in L. peruvianus). Costal silica bodies absent (L. peruvianus), or present and well developed (L. hieronymi); of L. hieronymi ‘panicoid-type’; somewhat dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs (round- and flat-topped); with the ribs very irregular in sizes. Midrib conspicuous (the large bundle having a slight abaxial keel); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with adaxial ‘sheath extensions’); forming ‘figures’ (I’s or anchors with all the bundles). Sclerenchyma not all bundle-associated (there being an abaxial, more or less interrupted lignified hypodermis). The ‘extra’ sclerenchyma in abaxial groups.

Special diagnostic feature. The lemma awns lateral and median, the median strongly flattened.

Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. 3 species.

Distribution, phytogeography, ecology. Tropical South America.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - L. peruvianus Hitchcock.

Special comments. Fruit data wanting.

Illustrations. • Lamprothyrsus hieronymi: Nicora & Rúgolo de Agrasar (1987). • Lamprothyrsus peruvianus, T.S. of leaf blade mid-region: this project. • Lamprothyrsus peruvianus, T.S. of lateral part 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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