Zygochloa S. T. Blake
From the Greek zygon (yoke, or pair) and chloa (grass), referring to dioecious spikelets.
Habit, vegetative morphology. Shrubby perennial (‘cane-grass’); rhizomatous (and tussock-forming). Culms 80–200 cm high; woody and persistent; to 0.9 cm in diameter (near the base); grooved on one side; branched above. Culm nodes glabrous. Culm internodes solid. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades broad to narrow; 4–10 mm wide (to 30 cm long); flat (short, stiff); without cross venation; disarticulating from the sheaths; a fringe of hairs.
Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality (on the same plant); female-only, or male-only. Plants outbreeding.
Inflorescence. Inflorescence a spatheate panicle of ‘bracteate’ heads; open. Inflorescence axes not ending in spikelets (interpreting one of the ‘bracts’ as a modified axis tip). Inflorescence spatheate (and ‘bracteate’); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes very much reduced (to a single spikelet accompanied by two basal bracts and the small, naked, bractlike axis tip, the units grouped into capitate heads); disarticulating; falling entire (the heads falling). Spikelets associated with bractiform involucres (each spikelet associated with the three chaffy, rigid-tipped ‘bracts’). The involucres shed with the fertile spikelets. Spikelets solitary; not secund; subsessile. Pedicel apices discoid. Spikelets not in distinct ‘long-and-short’ combinations.
Female-sterile spikelets. Male spikelets on separate individuals, in small bracteate heads 1–2 cm in diameter. Glumes similar, 5–7 nerved; lemmas 2, similar, awnless, 5 nerved, each with a male floret. Paleas conspicuous, with winged keels. 3 stamens, anthers 4 mm long, no gynoecium. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; without proximal incomplete florets; 2 floreted (both fertile). The lemmas awnless. Male florets 2; 3 staminate.
Female-fertile spikelets. Spikelets 6–10 mm long; lanceolate, or ovate; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; more or less equal; shorter than the adjacent lemmas; pointed, or not pointed; awnless; similar (papery). Lower glume 7–9 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; sterile. The proximal lemmas awnless; 5 nerved; becoming indurated.
Female-fertile florets 1. Lemmas abruptly acuminate; decidedly firmer than the glumes; smooth, or striate; becoming indurated (crustaceous); yellow in fruit; entire; pointed; awnless; hairless; non-carinate; having the margins inrolled against the palea; 5 nerved. Palea present; entire (ovate, abruptly acuminate); awnless, without apical setae; textured like the lemma; 2-nerved. Lodicules present; 2; fleshy. Stamens 0 (3 staminodes). Ovary glabrous. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit small (about 3 mm long). Hilum short.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. 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, or absent (not seen on male material); chloridoid-type; about 66 microns long; 9 microns wide at the septum. Microhair total length/width at septum 7.3. Microhair apical cells about 42 microns long. Microhair apical cell/total length ratio 0.64. Stomata common; 42–57 microns long. Subsidiaries parallel-sided, dome-shaped, and triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (solitary); silicified (when paired), or not silicified. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (the epidermis extensively, irregularly bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. Stems cane-like, spikelets in bracteate, globular 1–3.5 cm heads.
Taxonomy. Panicoideae; Panicodae; Paniceae.
Distribution, ecology, phytogeography. 1 species; Australia. Xerophytic; species of open habitats. Arid sandy and rocky places.
Australian. Central Australian.
References, etc. Morphological/taxonomic: Vickery 1975; Webster 1987. Leaf anatomical: this project.
Special comments. Fruit data wanting.
Illustrations. • Abaxial epidermis of leaf blade. • 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).
