Digastrium (Hackel) A. Camus
Sometimes referred to 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, 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 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.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae.
Distribution, ecology, phytogeography. 2 species; Australasia.
Paleotropical and Australian. Indomalesian. Papuan. North and East Australian. Tropical North and East Australian.
References, etc. Leaf anatomical: this project.
Special comments. Fruit data wanting.
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).