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The grass genera of the world

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

Peridictyon O. Seberg, S. Frederiksen & C. Baden

From the Greek peri- (around) and dictyon (a net), alluding to ‘netlike withering of the basal leaf sheaths’.

~ Festucopsis sancta (Janka) Meld.

Habit, vegetative morphology. Perennial; loosely caespitose. Culms (37–)47–80(–110) cm high; unbranched above; 2–3 noded. Culm nodes glabrous. Young shoots intravaginal. Leaves auriculate (the auricles (0.1-)0.3–0.7(-0.8) mm long). Sheath margins joined (the innovation leaves), or free. The basal sheaths disintegrating into a brownish mass of reticulate fibres. Leaf blades linear; narrow; (1–)1.6–2.6(–3.1) mm wide; not setaceous (junciform); rolled; not pseudopetiolate; disarticulating from the sheaths (‘with an abscission layer at junction of sheath and blade’). Ligule an unfringed membrane; truncate; ‘extremely short’.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence rather few spikeleted ((6-)7–13(-15)); a single spike ((5-)8–14(-17 cm long). Rachides flattened. Inflorescence espatheate. Spikelet-bearing axes persistent (?). Spikelets solitary; not secund; distichous (?); sessile.

Female-fertile spikelets. Spikelets (11–)12–19(–21) mm long; green; compressed laterally, or not noticeably compressed (?); disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus absent. Callus very short.

Glumes two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous; pointed; awned (the awn apical, 0.5–1.3 mm long); non-carinate; similar (lanceolate, leathery). Lower glume 2–4 nerved. Upper glume 3–6 nerved. Spikelets presumably with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 5–10. Lemmas entire (?); awned. Awns 1; median; apical (?); non-geniculate; much shorter than the body of the lemma (3–9 mm long). Lemmas hairless; glabrous; non-carinate. Palea present; relatively long (equalling to slightly shorter than the lemma); 2-nerved; 2-keeled. Palea keels hairy (ciliate above). Lodicules present; 2; presumably membranous; ciliate. Stamens 3. Anthers 4.2–6(–6.3) mm long. Ovary apically hairy. Stigmas 2.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea (to the lemma); medium sized (4.5–5.5 mm long); with hairs confined to a terminal tuft. Hilum long-linear. Endosperm containing only simple starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally (indistinguishable); of similar wall thickness costally and intercostally (thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (the sinuosity quite coarse, regular, associated with conspicuous pitting, and pits also conspicuous in the outside walls). Microhairs absent. Stomata absent or very rare. Intercostal short-cells absent or very rare; in cork/silica-cell pairs; silicified. Intercostal silica bodies rounded and crescentic. No macrohairs or prickles seen. Crown cells absent. Costal short-cells predominantly paired. Costal silica bodies present and well developed; rounded and crescentic.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (broadly round topped). Midrib conspicuous (by the rather pointed abaxial keel, and its larger abaxial girder); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (these small-celled, in the furrows). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries, the minor bundles with small adaxial strands and abaxial strands or girders); forming ‘figures’ (the primaries with massive I’s). Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in a continuous abaxial layer (linking the abaxial sclerenchyma of the bundles).

Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Mean diploid 2c DNA value unknown, but chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 1 species (P. sanctum).

Distribution, phytogeography, ecology. Greece and Bulgaria.

Species of open habitats; glycophytic. Calcareous, stony or rocky slopes.

References, etc. Morphological/taxonomic: Seberg et al. 1991. Leaf anatomical: studied by us.

Special comments. Morphological description scarcely adequate - e.g. spikelet orientation unknown. Fruit data wanting.

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.’.