Triodia R.Br.
From the Greek treis (three) and odous (tooth), referring to 3-toothed or 3-lobed lemmas.
Including Triodon Baumg.
Habit, vegetative morphology. Prickly perennial (‘porcupine grass’); caespitose. Culms 20–120(–240) cm high. Culm nodes glabrous. The shoots aromatic (often resinous), or not aromatic. Leaves auriculate, or non-auriculate. Sheath margins free. The sheaths often viscid. Leaf blades linear; narrow; not setaceous; acicular; hard, woody, needle-like; without abaxial multicellular glands; without cross venation; persistent; once-folded in bud; ligule present; a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike (T. spicata), or paniculate; open, or contracted; when contracted, spicate, or more or less irregular; with capillary branchlets (notably, in T. pascoeana), or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; subsessile to pedicellate.
Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings (by contrast with Symplectrodia). Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus present. Callus short; blunt.
Glumes two; more or less equal; shorter than the spikelets (to subequal); shorter than the adjacent lemmas, or long relative to the adjacent lemmas; hairless; glabrous; awnless; carinate, or non-carinate. Lower glume 1–7(–20) nerved. Upper glume 1–7(–20) nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. Spikelets without proximal incomplete florets.
Female-fertile florets 4–15. Lemmas becoming indurated (usually, in the body); usually incised; 3 lobed (or 3-toothed, rarely entire); not deeply cleft (at least by contrast with Plectrachne, the lobes usually being shorter than the body); awnless, or mucronate; hairy (usually, on the body - the lobes often glabrous); carinate to non-carinate; 3–20 nerved. Palea present; relatively long; 2-nerved; 2-keeled. Palea keels winged, or wingless. Lodicules present; 2; free; fleshy, or membranous; glabrous; heavily vascularized. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small; ellipsoid. Hilum short. Pericarp fused. Embryo large; not waisted. Endosperm containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or conspicuous and lacking (the abaxial grooves lacking across the leaf centre). Papillae absent (but abundant adaxially). Microhairs present (probably, but well hidden in the deep, narrow and hairy abaxial grooves - common enough adaxially); chloridoid-type; with ‘partitioning membranes’ (in T. scariosa). The ‘partitioning membranes’ in the basal cell. Stomata absent or very rare (or if present abaxially, confined to the grooves and unseen). Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section infolded permanently; circular. The adaxial channel parallel-sided, with a digitate base.
C4. The anatomical organization unconventional. Organization of PCR tissue Triodia type (i.e. the ‘sheaths’ lateral-only to the main bundles, and at least in the lateral parts of the blade, draping over adjacent bundles, so that many PCR cells are very distant from the vascular tissue). Biochemical type NAD–ME (T. scariosa); XyMS+. PCR sheath outlines even. PCR cells without a suberised lamella. PCR cell chloroplasts ovoid; with well developed grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (linking the adaxial and abaxial grooves, at least in the middle part of the blade where the PCR cells do not ‘drape’); with arm cells. Leaf blade ‘nodular’ in section (with narrow abaxial grooves), or with distinct, prominent adaxial ribs and ‘nodular’ in section (sometimes lacking the abaxial grooves towards the margins); with the ribs very irregular in sizes. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles; without colourless mesophyll adaxially (but the blade often with abaxial blocks of colourless tissue towards the margins). Bulliforms present in discrete, regular adaxial groups (but incorporated in the colourless tissue); associated with colourless mesophyll cells to form deeply-penetrating fans (incorporated in or linked with the colourless girders). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; forming ‘figures’. Sclerenchyma all associated with vascular bundles, or not all bundle-associated. The ‘extra’ sclerenchyma when present, in abaxial groups, or in a continuous abaxial layer.
Phytochemistry. Leaf blade chlorophyll a:b ratio 4.52–4.91.
Taxonomy. Chloridoideae; Triodieae.
Distribution, ecology, phytogeography. 35 species; Australia. Extreme xerophytic; species of open habitats. On arid, sandy or stony soils.
Australian. North and East Australian and Central Australian. Tropical North and East Australian and Temperate and South-Eastern Australian.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.
References, etc. Morphological/taxonomic: Burbidge 1953, 1960; Jacobs 1971. Leaf anatomical: Metcalfe 1960 and this project.
Illustrations. • General aspect. • General morphology. • Leaf blades. Triodia pungens. Hard, needlelike leaf blades. • Spikelet details. • Spikelet details. • Spikelet details. • Spikelet details. • Spikelet details. • Abaxial epidermis of leaf blade. • Transverse section of leaf blade. Triodia pungens. • Transverse section of leaf blade. Triodia hubbardii.
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).
