| # The grass genera of the world |

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

### Thellungia Stapf

~ Eragrostis, Sporobolus

Habit, vegetative morphology. Robust perennial; caespitose. Culms 80–150 cm high; herbaceous. Culm nodes glabrous. Leaves mostly basal; non-auriculate. Leaf blades narrow; 2–5 mm wide; flat; without abaxial multicellular glands; not pseudopetiolate; without cross venation; persistent. Ligule a fringe of hairs.

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

Inflorescence. Inflorescence paniculate; contracted (the primary branches short, erect-appressed); spicate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; subsessile.

Female-fertile spikelets. Spikelets about 4 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret (all the florets hermaphrodite?); hairless; the rachilla extension (when present) with incomplete florets, or naked. Hairy callus absent.

Glumes two; very unequal; shorter than the adjacent lemmas; pointed; awnless; similar (membranous, narrow). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets; without proximal incomplete florets.

Female-fertile florets (1–)3–4. Lemmas similar in texture to the glumes (membranous); not becoming indurated; entire; pointed; awnless; hairless; glabrous; carinate. The keel wingless. Lemmas 1 nerved. Palea present; conspicuous but relatively short (about one half the lemma length); entire (pointed); awnless, without apical setae; not indurated; 2-nerved. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit small; compressed laterally. Hilum short. Pericarp free. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type (the basal and apical cells both short). Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs (21–)22.5–24(–27) microns long. Microhair basal cells 18 microns long. Microhairs 11.4–14.4 microns wide at the septum. Microhair total length/width at septum 1.7–2.1. Microhair apical cells 10.5–13.5 microns long. Microhair apical cell/total length ratio 0.44–0.56. Stomata common; 27–36 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (some solitary, a few threes). Intercostal silica bodies absent. Costal short-cells conspicuously in long rows (but in places the ‘short-cells’ are quite long). Costal silica bodies present in alternate cell files of the costal zones; saddle shaped and ‘panicoid-type’, or tall-and-narrow (a few, bordering the veins); the panicoid type cross shaped (but saddles and intermediates predominating); not sharp-pointed.

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

C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; 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 each groove); in simple fans (these predominating, with large, deeply penetrating median cells), or associated with colourless mesophyll cells to form deeply-penetrating fans (a few). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primary bundles only - the rest mostly with strands adaxially); forming ‘figures’ (all the primary bundles with massive ‘anchors’). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Zoysieae; Sporobolinae (as a synonym of Sporobolus). 1 species (T. advena).

Distribution, phytogeography, ecology. Australia.

References, etc. Leaf anatomical: studied by us.

Special comments. Bridging Sporobolus and Eragrostis, and incompletely separable from the latter in terms of the current descriptions.

Illustrations. • Thellungia advena: Hook. Ic. Pl. 32 (1933). • Thellungia advena: Lazarides (1981). • Thellungia advena, 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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