The grass genera of the world

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

Thyridachne C.E. Hubb.

From the Greek thyridos (a window) and achne (chaff), alluding to the peculiar lower lemma.

Including Tisserantiella Mimeur

Habit, vegetative morphology. Annual. Culms herbaceous. Leaf blades linear; narrow; without cross venation. Ligule membranous.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence a single raceme, or paniculate (narrow, slender, spiciform); contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets mostly paired; sessile and pedicellate. Pedicel apices minutely cupuliform. Spikelets consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite.

Female-fertile spikelets. Spikelets abaxial; compressed dorsiventrally (falcate in lateral view); falling with the glumes; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; hairless; awnless; non-carinate; very dissimilar (the G1 small, broad, sub-orbicular and thinly membranous, the G2 gibbous and enveloping the spikelet by its inflexed margins, oblong-elliptical, obtusely bi- to tri-lobed at the summit, basally membranous, leathery below but hyaline at the base of the median line). Lower glume much shorter than half length of lowest lemma (about a quarter as long as G2); 0 nerved. Upper glume distinctly saccate (gibbous); 5 nerved (obscurely). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate; male, or sterile. The proximal lemmas apically obscurely trilobed, channelled down the back, the channel membranous and enlarging below to form a ‘window’, the margins and apex also membranous, leathery elsewhere; awnless; obscurely 3 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas (equalling G2); thinly leathery.

Female-fertile florets 1. Lemmas broadly oval; less firm than the glumes to similar in texture to the glumes (somewhat leathery or cartilaginous, with membranous apices); not becoming indurated; entire; blunt; awnless; hairless; non-carinate; 3 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; keel-less (or flat). Lodicules absent. Stamens 3; with free filaments. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit compressed dorsiventrally (plano-concave to plano-convex). Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much more regularly rectangular); of similar wall thickness costally and intercostally (fairly thick walled). Intercostal zones with typical long-cells. Mid-intercostal long-cells more or less rectangular; having markedly sinuous walls (the sinuosity very coarse, irregular). Microhairs present, or absent (very scarce - commoner adaxially); panicoid-type; 21–27 microns long; 5.7–6 microns wide at the septum. Microhair total length/width at septum 3.5–4.7. Microhair apical cells 12.6–21 microns long. Microhair apical cell/total length ratio 0.6–0.78. Stomata common; 33–39 microns long. Subsidiaries non-papillate; rather low triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (the pairs tiny, superposed); silicified. Intercostal silica bodies rounded. No macrohairs or prickles seen. Costal short-cells predominantly paired. Costal silica bodies rounded (predominating), or crescentic, or tall-and-narrow (a few).

Transverse section of leaf blade, physiology. C3 (with large mesophyll lacunae); XyMS+. Leaf blade with distinct, prominent adaxial ribs (the ribs topped by clusters of large, thin walled macrohairs); with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (if the large, thin walled ‘colourless’ tissue between the bundles and the ad- and abaxial fibre groups is interpreted as sclerenchyma). Sclerenchyma all associated with vascular bundles (apart from large fibre groups in the distended blade margins).

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Anthephorinae. 1 species (T. tisserantii).

Distribution, phytogeography, ecology. Tropical Africa.

Helophytic (in shallow pools); glycophytic.

References, etc. Morphological/taxonomic: Hubbard 1949. Leaf anatomical: studied by us.

Illustrations. • T. tisserantii: Jacques-Félix, 1962. • Abaxial epidermis of leaf blade of T. tisserantii: 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.’.