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The grass genera of the world

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

Spinifex L.

From the Latin spina (a thorn) and facere (to make), alluding to sharp pointed leaves and/or female spikelet clusters.

Type species: Type: S. squarrosus L.

Including Ixalum Forst.

Habit, vegetative morphology. Perennial; rhizomatous and caespitose. Culms 50–100 cm high; herbaceous. Culm nodes hairy, or glabrous. Culm leaf sheaths rounded. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; hard, woody, needle-like, or not needle-like; without cross venation; persistent; rolled in bud. Ligule a fringe of hairs.

Reproductive organization. Plants dioecious; with hermaphrodite florets, or without hermaphrodite florets. The spikelets all alike in sexuality (on the same plant); female-only, or hermaphrodite (? - the female florets often containing well formed stamens), or male-only. Plants outbreeding.

Inflorescence. Inflorescence very peculiar - the female-fertile (hermaphrodite) spikelets solitary at the bases of long, bare rachides, which are bristle-like and clustered in dense spatheate umbels: the latter fall entire and are blown about; male spikelets in rigid spikes clustered in spatheate umbels; the umbel deciduous in its entirety. Inflorescence axes not ending in spikelets (the female-fertile spikelets solitary at the bases of the long, pointed rachides). Inflorescence spatheate. Spikelet-bearing axes persistent. Spikelets associated with bractiform involucres (consisting of spathes). The involucres shed with the fertile spikelets. Spikelets subsessile. Pedicel apices cupuliform.

Female-sterile spikelets. The male spikelets on separate plants, in spatheate umbels of rigid spikes, the spikelets falling from their pedicels; rachilla not prolonged, no hairy callus. Glumes unequal, shorter than the adjacent lemma, convex on the back, awnless, 3–7 nerved. Lemmas 2, similar, awnless, 5 nerved, each with a staminate flower. Paleas 2-nerved, about equalling the lemmas. Lodicules 2, often united, glabrous. Stamens 3, ovary rudimentary. 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.

Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate; compressed dorsiventrally; falling with the glumes (female-fertile spikelets falling with the umbel, tardily disarticulating from their pedicels). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; hairy, or hairless; awnless; non-carinate; similar (acute, papery, entire). Lower glume 7–11 nerved. Upper glume 7–11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 5 nerved; exceeded by the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (finally); smooth; becoming indurated to not becoming indurated; yellow in fruit; awnless; hairless; non-carinate; with a clear germination flap; 3–11 nerved. Palea present; relatively long; textured like the lemma; indurated; 2-nerved. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 3, or 0 (then 3 staminodes). Ovary apically glabrous. Styles fused. Stigmas 2; white.

Fruit, embryo and seedling. Fruit medium sized; ellipsoid; compressed dorsiventrally. Hilum short. Embryo large; waisted.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina curved.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (but commonly obscured by the macrohairs). 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 to having straight or only gently undulating walls. Microhairs present; panicoid-type; 108–120 microns long. Microhair apical cells 72–80 microns long. Microhair apical cell/total length ratio 0.67. Stomata common; 24–30 microns long. Subsidiaries parallel-sided, or dome-shaped, or triangular (basically, triangles with the apices truncated to varying extents). Guard-cells overlapped by the interstomatals (the stomata in deep pits). Intercostal short-cells common; in cork/silica-cell pairs, or not paired (then solitary); silicified (rarely), or not silicified. Intercostal silica bodies tall-and-narrow, or cubical. Numerous large, thick-walled macrohairs present. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present and well developed, or poorly developed (or few), or absent; horizontally-elongated smooth (sometimes, a few), or tall-and-narrow (or more or less cuboid, with points), or ‘panicoid-type’; sometimes cross shaped, or dumb-bell shaped; sharp-pointed (i.e., the cuboid forms), or not sharp-pointed.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (1 species); XyMS– (or ‘XyMS variable’). PCR sheath outlines uneven. PCR sheath extensions present. Maximum number of extension cells 3–10. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles (rarely). Bulliforms present in discrete, regular adaxial groups (the groups sometimes poorly defined); in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles scattered.

Special diagnostic feature. Female inflorescence a large, deciduous globular head of sessile, bristle-tipped racemes.

Cytology. Chromosome base number, x = 9. 2n = 18. 2 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 4 species.

Distribution, phytogeography, ecology. Eastern Asia, Indomalayan region, Pacific, Australia.

Xerophytic; species of open habitats; halophytic. Binding coastal sand dunes.

Rusts and smuts. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • S. hirsutus: P. Beauv. (1812). • S. hirsutus: • S. hirsutus, hermaphrodite: La Billardierre and Houton (1804), Novae Hollandiae Plantarum 2. • S. hirsutus, male: La Billardierre and Houton (1804), Novae Hollandiae Plantarum 2. • Caryopsis of S. hirsutus (hilum): this project. Spinifex hirsutus. Dorsiventrally compressed, with short (punctiform) hilum. • Caryopsis of S. hirsutus (embryo): this project. Spinifex hirsutus. ‘Large’, waisted embryo. • S. sericeus, abaxial epidermis of leaf blade: this project. • S. hirsutus, abaxial epidermis of leaf blade: this project. • S. hirsutus, TS of leaf blade: this project

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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: 13th November 2017.’.