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The grass genera of the world

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

Digastrium (Hackel) A. Camus

~ Ischaemum

Habit, vegetative morphology. Perennial. Culms herbaceous. Culm nodes hairy, or glabrous. Leaves not basally aggregated; non-auriculate. Leaf blades broad, or narrow; without cross venation; persistent. Ligule present; an unfringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile; overtly heteromorphic; all in heterogamous combinations.

Inflorescence. Inflorescence of spicate main branches, or a single raceme (the spike-like racemes with thick, inflated joints and pedicels); often digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’; solitary to clustered; with substantial rachides (the joints thick, inflated); disarticulating; disarticulating at the joints. ‘Articles’ non-linear. Spikelets paired; not secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets sterile.

Female-sterile spikelets. The pedicellate spikelets sterile, reduced to glumes.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; awnless. Lower glume not pitted; relatively smooth; 5–7 nerved. Upper glume 5–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate; male. The proximal lemmas awnless; not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes; incised; 2 lobed (bifid); awned. Awns 1; median; from a sinus; geniculate. Lemmas hairless; non-carinate; 3 nerved. Palea present; 2-nerved (?). Lodicules present; 2; free; fleshy; ciliate, or glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; many or several per cell. Long-cells of similar wall thickness costally and intercostally (rather thin walled). Intercostal zones mainly with typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type and chloridoid-type (the basal cells fairly long, the apical cells sometimes partially collapsing but quite thick walled, hemispherical to somewhat elongated); (24–)25.5–27(–30) microns long; (7.5–)8.4–9 microns wide at the septum. Microhair total length/width at septum 2.7–3.6. Microhair apical cells 7.5–9–9.6 microns long. Microhair apical cell/total length ratio 0.29–0.37. Stomata common; (27–)28.5–30(–36) microns long. Subsidiaries papillate; triangular. Intercostal short-cells common to absent or very rare; not paired (solitary). Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly dumb-bell shaped; sharp-pointed.

Transverse section of leaf blade, physiology. C4. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the major bundles); forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Ischaeminae (?). 2 species.

Distribution, phytogeography, ecology. Australasia.

References, etc. Leaf anatomical: studied by us - D. fragile (Hack.) A. Camus.

Special comments. Fruit data wanting. Illustrations. • D. fragile, as Ischaemum: Stanley & Ross, Fl. S.E. Queensland (1989)

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.’.