The grass genera of the world

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

Thyridolepis S. T. Blake

From the Greek thyridos (a window) and lepis (a scale), alluding to the peculiar lower glume.

Type species: Type: T. mitchelliana (Nees) S.T.Blake.

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 leaf sheaths rounded. 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, all 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 apically 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.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Neurachneae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Neurachninae. 3 species.

Distribution, phytogeography, ecology. Australia.

Xerophytic; species of open habitats. Dry grassland and scrub.

Economic aspects. Important native pasture species: T. mitchelliana (drought tolerant).

References, etc. Morphological/taxonomic: Blake 1972b. Leaf anatomical: Hattersley et al. 1982; studied by us - T. mitchelliana (Nees) Blake, T. multiculmis (Pilger) Blake, T. xerophila (Domin) Blake.

Illustrations. • T. mitchelliana, general morphology, details: Blake, 1972. • Intravaginal culm branching of T. mitchelliana. • General aspect, inflorescence of T. mitchelliana. • T. mitchelliana, as Neurachne: Hook. Ic. Pl. 13 (1877–79). • Spikelets of T. mitchelliana and T. multiculmis. • T. mitchelliana, close-up of inflorescence, glume details: this project. Thyridolepis mitchelliana. Abaxial spikelets, the lower (outer) glumes with a ‘window’ surmounted by bristles. • Spikelet of T. xerophylla. • Germinating caryopsis and seedling of T. mitchelliana. • T. multiculmis, abaxial epidermis of leaf blade: this project. • T. mitchelliana, abaxial epidermis of leaf blade: this project. • T. xerophylla, abaxial epidermis of leaf blade: this project. • T. mitchelliana, fluorescence image of leaf blade TS: this project

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or 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, and classifications. See also Guidelines for using data taken from Web publications.

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: 11th December 2017.’.