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; a fringed membrane.
Reproductive organization. Plants bisexual, 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. Spikelets with proximal incomplete 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 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 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.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae.
Distribution, ecology, phytogeography. 1 species; northern Australia. Species of open habitats. Grassy plains.
Australian. North and East Australian. Tropical North and East Australian.
References, etc. Leaf anatomical: this project.
Illustrations. • Abaxial epidermis of leaf blade
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).
