| # The grass genera of the world |

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

### Tetrarrhena R.Br.

From the Greek tetra (four) and arrhen (male), alluding to four stamens.

~ Ehrharta

Habit, vegetative morphology. Perennial; stoloniferous and decumbent. Culms woody and persistent to herbaceous; scandent (often), or not scandent (wiry, often long and scrambling, ‘sometimes capable of entangling a horse’); branched above. The branching simple. Culm nodes glabrous. Culm internodes hollow. Young shoots extravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; flat (or concave), or rolled; not pseudopetiolate; cross veined (rarely), or without cross venation; persistent. Ligule an unfringed membrane to a fringed membrane; truncate; short. Contra-ligule absent.

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

Inflorescence. Inflorescence few spikeleted; a single raceme (spike-like, the axis flexuous); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; subsessile.

Female-fertile spikelets. Spikelets 4.8–7 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; shorter than the adjacent lemmas; not pointed (truncate); awnless; similar (leathery to scarious). Lower glume 1 nerved. Upper glume 5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 2; epaleate; sterile. The proximal lemmas awnless; faintly 7 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (tough); not becoming indurated.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (leathery); not becoming indurated; entire; blunt; awnless; hairless; carinate to non-carinate; 7 nerved. Palea present; relatively long, or conspicuous but relatively short; entire (acute); awnless, without apical setae; thinner than the lemma (membranous); not indurated; 1-nerved; one-keeled (laterally compressed). Lodicules present (large); 2; membranous; ciliate, or glabrous; toothed, or not toothed; relatively heavily vascularized (cf. Ehrharta). Stamens 4 (usually), or 2 (T. oreophila). Anthers 2–3 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases.

Fruit, embryo and seedling. Fruit compressed laterally. Hilum short. Embryo small. Endosperm containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with a negligible mesocotyl internode.

Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 5 veined.

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. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (30–)34–60(–63) microns long; 4.5–5.1 microns wide at the septum (T. oreophila), or 9.6–18 microns wide at the septum. Microhair total length/width at septum 2.1–7.1, or 10 (in T. oreophila). Microhair apical cells (10.5–)12–35(–36) microns long. Microhair apical cell/total length ratio 0.31–0.71. Stomata absent or very rare; 22.5–45 microns long. Subsidiaries dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or rounded (or oval), or crescentic. Costal short-cells conspicuously in long rows. Costal silica bodies rounded, or ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. PBS cells without a suberised lamella. Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma; without adaxial palisade; without arm cells; without fusoids. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib not readily distinguishable; 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; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Ehrharteae. Soreng et al. (2015): Oryzoideae; Ehharteae. 5 species.

Distribution, phytogeography, ecology. Australia.

Shade species.

Rusts and smuts. Rusts — Puccinia.

References, etc. Morphological/taxonomic: Vickery 1975; Willemse 1982. Leaf anatomical: Metcalfe 1960; studied by us - T. distichophylla R. Br., T. juncea R. Br., T. laevis R. Br., T. oreophila D.I. Morris.

Illustrations. • Tetrarrhena juncea, as tenacissima: Hooker (1860), Erebus and Terror Voyage, 3. • General aspect and spikelet of T. laevis. • Tetrarrhena laevis, abaxial epidermis of leaf blade: this project. • Tetrarrhena juncea, TS 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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