The grass genera of the world

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L. Watson and M. J. Dallwitz

Triodia R.Br.

From the Greek treis (three) and odous (tooth), referring to 3-toothed or 3-lobed lemmas.

Including Triodon Baumg.

Excluding Plectrachne

Habit, vegetative morphology. Prickly perennial (‘porcupine grass’); caespitose. Culms 20–120(–240) cm high. Culm nodes glabrous. Plants conspicuously armed. 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; not pseudopetiolate; 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. About 40 species (with species formerly refered to Plectrachne excluded); Australia. Extreme xerophytic (with species formerly referred to Plectrachne excluded); 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. This description does not account for generic re-circumscriptions involving transference of Plectrachne species to Triodia (see Lazarides, in Austral. Syst. Bot. 10: 381–489 (1997). Leaf anatomical: Metcalfe 1960 and this project.

Illustrations. • T. pungens: Gardner, 1952. • T. racemigera, T. triticoides: Gardner, 1952. • Needle-like leaf blade tips of T. pungens. • Spikelet details (T. basedowii, T. lanigera, T. pungens). • Spikelet details (T. angusta, T. irritans, T. cunninghamii, T. fitzgeraldii, T. secunda). • Spikelet details (T. brizoides, T. intermedia, T. longiceps). • Spikelet details (T. pungens). • Spikelet details (T. procera, T. secunda, T. triticoides). • Abaxial epidermis of leaf blade (T. pungens). • T.S. leaf blade detail, 'draping' PCR tissue (T. hubbardii). • T.S. leaf blade, fluorescence image (T. pungens). • Leaf blade T.S.: immunofluorescent-labelled Rubisco in T. pungens (Hattersley, Watson and Osmond 1977). • Microhair of Triodia scariosa: longitudinal EM sections (Amarasinghe). • Microhair of Triodia scariosa: ultrastructural details of the basal cell (Amarasinghe). • Microhair of Triodia scariosa: more ultrastructural details of the basal cell (Amarasinghe)

The descriptions are offered for casual browsing only. We strongly advise against extracting comparative information from them. This is much more easily achieved using 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, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG).

Cite this publication as: ‘Watson, L., 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: 7th December 2015.’.