The grass genera of the world

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

Arthragrostis Lazarides

From the Greek arthro (jointed) and agrostis (a forage plant, a kind of grass), in reference to the disarticulating spikelet-bearing axes.

Type species: Type: A. deschampsioides (Domin) Lazarides.

Habit, vegetative morphology. Annual. Culms 20–60 cm high; herbaceous. Culm nodes glabrous. Culm leaf sheaths rounded. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; 2–5 mm wide (to 10 cm long); flat; without cross venation. Ligule present; a fringed membrane.

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

Inflorescence. Inflorescence paniculate; open (7–10 cm long). Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the primary inflorescence branches deciduous). Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; solitary; not secund; pedicellate. Pedicel apices truncate. Spikelets not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 4–4.9 mm long; lanceolate; compressed dorsiventrally; falling with the glumes; with a distinctly elongated rachilla internode between the glumes and with distinctly elongated rachilla internodes between the florets. The upper floret conspicuously stipitate. The stipe beneath the upper floret filiform (not appendaged); homogeneous. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; hairless (G1 glabrous, G2 scabrid); pointed (G2 acuminate), or not pointed (G1 acute to rounded); awnless; non-carinate; very dissimilar. Lower glume 7 nerved. Upper glume 11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 9–11 nerved; considerably longer than the upper lemmas; less firm than the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas acute; decidedly firmer than the glumes (cartilaginous); smooth; white in fruit; entire; pointed to blunt; awnless; hairless; glabrous; non-carinate; having the margins inrolled against the palea; with a clear germination flap; obscurely nerved. Palea present; relatively long; entire; awnless, without apical setae; cartilaginous, like the lemma. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals very much narrower). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. With numerous large, cushion-based macrohairs. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly small butterfly shaped and dumb-bell shaped.

Transverse section of leaf blade, physiology. C4; XyMS+. PCR sheath outlines uneven. PCR sheath extensions absent. Leaf blade adaxially flat. Midrib conspicuous (via a prominent, flat abaxial keel, and a large abaxial sclerenchyma girder associated with the median bundle); having a conventional arc of bundles (there being a smaller lateral on either side of the median). Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent (the larger bundles with small abaxial strands or girders only). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Panicinae. 3 species.

Distribution, phytogeography, ecology. Australia.

Mesophytic; species of open habitats. In scrub.

References, etc. Morphological/taxonomic: Lazarides 1985. Leaf anatomical: studied by us - A. aristispicula B.K. Simon, A. deschampsioides (Domin) Lazarides.

Special comments. Fruit data wanting. Illustrations. • A. deschampsioides, 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: 11th December 2017.’.