Thyridolepis S. T. Blake
From the Greek thyridos (a window) and lepis (a scale), alluding to the peculiar lower glume.
Habit, vegetative morphology. Perennial (with basal scaly, woolly cataphylls); caespitose, or decumbent. Culms 15–50 cm high; woody and persistent, or herbaceous; tuberous, or not tuberous. Culm nodes hairy, or glabrous. Culm internodes solid. Young shoots extravaginal and intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear to ovate; narrow; 1.5–4.5 mm wide; not setaceous; somewhat pseudopetiolate; without cross venation; disarticulating from the sheaths; rolled in bud; ligule present; a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile (the lowermost spikelets being reduced). Plants exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence a single raceme (spikelike, bristly); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; shortly pedicellate. Pedicel apices oblique, or discoid.
Female-fertile spikelets. Spikelets 4–7.5 mm long; oblong, or elliptic, or lanceolate; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present.
Glumes two; more or less equal; long relative to the adjacent lemmas; dorsiventral to the rachis; hairy; awnless; non-carinate; very dissimilar (both leathery, the lower blunt, with a transverse row of tubercle-based bristles along the top of a rectangular, semi-transparent or pigmented ‘window’, the upper broader, rostrate, with tufts of tubercle-based bristles along the margins). Lower glume 7–11 nerved. Upper glume 7–11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, reduced. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 5 nerved; more or less equalling the female-fertile lemmas; becoming indurated (not gibbous).
Female-fertile florets 1. Lemmas similar in texture to the glumes; not becoming indurated (thinly rigid as in Paraneurachne, by contrast with Neurachne); brown in fruit; entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 3–5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved. Lodicules present, or absent; when present, 2; free; fleshy; glabrous. Stamens 3. Anthers very short; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2 (and only 2 styles, no appendage on the grain).
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with a negligible mesocotyl internode.
Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (36–)48–72(–75) microns long; 5.4–9.6 microns wide at the septum. Microhair total length/width at septum 4.3–10.6. Microhair apical cells (21–)25–38(–42) microns long. Microhair apical cell/total length ratio 0.47–0.64. Stomata common; 21–39 microns long. Subsidiaries triangular, or dome-shaped and triangular (T. xerophila), or parallel-sided, dome-shaped, and triangular (T. multiculmis); including both triangular and parallel-sided forms on the same leaf, or not including both parallel-sided and triangular forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs, or not paired; silicified, or not silicified. Two of the species with cushion-based macrohairs and/or prickles. Crown cells present, or absent. Costal short-cells conspicuously in long rows (but sometimes also short rows, solitaries, pairs). Costal silica bodies ‘panicoid-type’; cross shaped, butterfly shaped, dumb-bell shaped, and nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. PBS cells without a suberised lamella. Mesophyll with radiate chlorenchyma; with adaxial palisade; Isachne-type. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (sometimes associated with/comprising hair cushions); often in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (combining strong abaxial girders with adaxial strands, the latter linked with the bundles by vertically-elongated colourless cells). Sclerenchyma all associated with vascular bundles (apart from strong marginal groups).
Special diagnostic feature. Lower glume with a rectangular window, surmounted by bristles.
Cytology. Chromosome base number, x = 9. 2n = 18 and 36. 2 and 4 ploid.
Taxonomy. Panicoideae; Panicodae; Neurachneae.
Distribution, ecology, phytogeography. 3 species; Australia. Xerophytic; species of open habitats. Dry grassland and scrub.
Australian. North and East Australian and Central Australian. Tropical North and East Australian.
Economic importance. Important native pasture species: T. mitchelliana (drought tolerant).
References, etc. Morphological/taxonomic: Blake 1972b. Leaf anatomical: Hattersley et al. 1982; this project.
Illustrations. • General morphology. • Vegetative detail. Thyridolepis mitchelliana. Intravaginal culm branching. • General aspect, inflorescence. Thyridolepis mitchelliana. • Spikelet. • Inflorescence detail. Thyridolepis mitchelliana. Abaxial spikelets, the lower (outer) glumes with a ‘window’ surmounted by bristles. • Spikelet. • Abaxial epidermis of leaf blade. • Abaxial epidermis of leaf blade. • Abaxial epidermis of leaf blade. • Transverse section of leaf blade. Thyridolepis mitchelliana.
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).
