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The grass genera of the world

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

Psilathera Link

~ Sesleria

Habit, vegetative morphology. Perennial. Culms 3–10 cm high; herbaceous. Leaves non-auriculate. Leaf blades narrow; 1–1.5 mm wide; setaceous, or not setaceous; not pseudopetiolate; without cross venation. Ligule an unfringed membrane; not truncate; 1–2 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile; overtly heteromorphic (the sterile spikelets represented by ovate to lanceolate bracts at the base of the inflorescence).

Inflorescence. Inflorescence paniculate; contracted; capitate, or more or less ovoid (6–10 x 4–6 mm); espatheate (but with bracts at base of inflorescence); not comprising ‘partial inflorescences’ and foliar organs. Spikelets not secund.

Female-sterile spikelets. The sterile spikelets vestigial, represented by bracts at the base of the inflorescence.

Female-fertile spikelets. Spikelets 2 mm long; not noticeably compressed; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus present.

Glumes two; more or less equal; long relative to the adjacent lemmas; awned (the awns to 2 mm long, straight or hooked), or awnless (but mucronate); carinate; similar (ovate, abruptly contracted above). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets without proximal incomplete florets.

Female-fertile florets 1–2. Lemmas decidedly firmer than the glumes; not becoming indurated; incised; 5 lobed (toothed); not deeply cleft; awned. Awns 5; median and lateral (via the excurrent veins); the median similar in form to the laterals; non-geniculate; about as long as the body of the lemma to much longer than the body of the lemma. The lateral awns shorter than the median (the median to 1.5 mm long, the laterals about 1 mm). Lemmas non-carinate (dark blue, broadly ovate); without a germination flap; 5 nerved. Palea present; relatively long (exceeding the lemma); awned (with two 1–1.5 mm awns); 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 3. Ovary apically hairy. Stigmas 2.

Fruit, embryo and seedling. Fruit small (2 mm long); with hairs confined to a terminal tuft. Hilum short. Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation fairly conspicuous. Papillae absent. Long-cells fairly markedly different in shape costally and intercostally (the costals narrower and more consistently rectangular); of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells fusiform, or rectangular and fusiform (in places); having straight or only gently undulating walls (the walls heavily pitted). Microhairs absent. Stomata absent or very rare (none seen). Intercostal short-cells absent or very rare. With a few costal prickles. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (solitary and a few short rows). Costal silica bodies present and well developed (but scarce); horizontally-elongated crenate/sinuous and horizontally-elongated smooth.

Transverse section of leaf blade, physiology. C3; XyMS+. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (round topped, one ber bundle). Midrib conspicuous (by its position on the fold of the blade, and the pointed keel); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (? - not clear in the material seen); if present, in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma (the sclerenchyma confined to a small abaxial strand in the keel, and marginal fibre groups). Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Seslerieae. Soreng et al. (2015): Pooideae (as a synonym?); Poodae; Poeae; Sesleriinae. 1–2 species (P. ovata, P. tenella).

Distribution, phytogeography, ecology. Southern & central Europe.

References, etc. Leaf anatomical: studied by us - P. tenella (Host) Link.

Illustrations. • P. ovata, as Cynosurus: Sturm and Sturm (1798), Deutschlands Flora 2

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.’.