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The grass genera of the world

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

Spathia Ewart

Habit, vegetative morphology. Annual; caespitose. The flowering culms leafy. Culms 20–75 cm high; herbaceous; branched above. Culm nodes hairy. Culm internodes solid. Leaves not basally aggregated; non-auriculate. The sheaths usually inflated. Leaf blades narrow; 2–4 mm wide (reducing in length on the upper culm, where the sheaths become enlarged to constitute spathes); without cross venation; disarticulating from the sheaths. Ligule a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic (the pedicellate spikelets less hairy, awnless); in both homogamous and heterogamous combinations (each raceme with one basal, homogamous pair). Plants exposed-cleistogamous.

Inflorescence. Inflorescence of spicate main branches (of sessile or subsessile ‘racemes’); digitate; spatheate (with one broad, membranous spathe enclosing the inflorescence); a complex of ‘partial inflorescences’ and intervening foliar organs (up to 3 partial inflorescences), or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’; clustered (3–5); with very slender rachides; disarticulating; disarticulating at the joints. ‘Articles’ linear; not appendaged; disarticulating obliquely; densely long-hairy (with brown hairs). Spikelets paired; not secund; sessile and pedicellate, or subsessile and pedicellate; consistently in ‘long-and-short’ combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only.

Female-sterile spikelets. The less hairy, awnless pedicellate spikelet with two glumes and a floret containing 2 stamens, the callus short and oblong. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes (two); 1 floreted. The lemmas awnless. Male florets 2 staminate.

Female-fertile spikelets. Spikelets 5.5–6.2 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. The callus hairs brown (long, dense). Callus blunt.

Glumes two; more or less equal; free; hairy (the hairs brown); awnless; very dissimilar (the lower bicarinate and blunt, the upper cymbiform and pointed). Lower glume two-keeled; convex on the back; 7–9 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; sterile. The proximal lemmas awnless; 0 nerved; less firm than the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas stipe-like beneath the awn; less firm than the glumes; not becoming indurated; entire; awned. Awns 1; median; apical; geniculate; hairless (glabrous); much longer than the body of the lemma. Lemmas non-carinate; 0–1 nerved. Palea absent. Lodicules present; 2; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers about 0.6 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm hard; containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae slightly over-arching the stomata, or not over-arching the stomata; consisting of one oblique swelling per cell. 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; 48–60 microns long; (3.9–)5.4–5.7(–6) microns wide at the septum. Microhair total length/width at septum 9.4–13. Microhair apical cells (16.5–)19.5–22.5(–24) microns long. Microhair apical cell/total length ratio 0.32–0.47. Stomata common; (22.5–)24–25.5(–27) microns long. Subsidiaries triangular. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’ (large); not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles (rarely); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups to not present in discrete, regular adaxial groups; sometimes more or les in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 1 species (S. neurosa).

Distribution, phytogeography, ecology. Northern Australia.

Species of open habitats. Grassy plains.

References, etc. Leaf anatomical: studied by us.

Illustrations. • S. neurosa: Lazarides (1981). • S. neurosa, abaxial epidermis of leaf blade: this project. • S. neurosa, 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.’.