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The grass genera of the world

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

Lygeum Loefl. ex L.

Including Linospartum Adans., Spartum P. Beauv.

Habit, vegetative morphology. Wiry perennial; rhizomatous (the rhizomes scaly). Culms 30–70 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades narrow (junciform); without cross venation; persistent; once-folded in bud. Ligule present; an unfringed membrane; not truncate (acute); 7 mm long.

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

Inflorescence. Inflorescence reduced to a single spikelet; of one terminal spikelet, enclosed in an indurated spathe until it protrudes from the side at maturity; spatheate (the hard spathes ovate, acute or with a laminate tip). Spikelet-bearing axes very much reduced (to a single spikelet).

Female-fertile spikelets. Spikelets unconventional (through apparent absence of glumes, and congenital fusion of lemmas and paleas); 35–45 mm long; compressed laterally; the spikelet falling whole. Rachilla terminated by a female-fertile floret.

Glumes absent. Spikelets with female-fertile florets only.

Female-fertile florets 2. Lemmas leathery, 2 cm long, the two connate by their margins over the lower half into a rigid, hairy tube, the upper halves free; becoming indurated; awnless; hairy (below, glabrous above); non-carinate; 9 nerved. Palea present (the two connate by their backs below); relatively long (3–4 cm: much exceeding the lemms); awnless, without apical setae; 2-nerved. Lodicules absent. Stamens 3. Anthers about 15 mm long; not penicillate. Ovary apically glabrous. Styles fused (assuming the ostensibly single style represents fusion of two). Stigmas 1.

Fruit, embryo and seedling. Fruit medium sized (8–9 mm long); fusiform. Hilum long-linear. Embryo small. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast.

Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 7 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (rather thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present (but infrequent); chloridoid-type (sic: large and spectacular, in the material seen); 72–93 microns long; 21.6–24 microns wide at the septum. Microhair total length/width at septum 3–4.3. Microhair apical cells 24–25.5 microns long. Microhair apical cell/total length ratio 0.27–0.33. Stomata common; (45–)54–57 microns long. Subsidiaries triangular. Guard-cells overlapped by the interstomatals. Intercostal short-cells common; silicified. Intercostal silica bodies rounded. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (rarely). Costal silica bodies exclusively rounded; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; 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 (in the furrows, small and variable in size cf. Ammophila). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; forming ‘figures’. Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups (these columnar); opposite some of the furrows.

Phytochemistry. Leaves without flavonoid sulphates.

Special diagnostic feature. Plant coarsely tufted, with wiry leaf blades, the inflorescence of one very peculiar spikelet enclosed in a sheath.

Cytology. Chromosome base number, x = 10. 2n = 40 (the chromosomes ‘large’). 4 ploid (the 40 chromosomes large).

Classification. Watson & Dallwitz (1994): Stipoideae; Lygeae. Soreng et al. (2015): Pooideae; Lygeae. 1 species (L. spartum).

Distribution, phytogeography, ecology. Mediterranean.

Xerophytic; species of open habitats.

Economic aspects. Esparto grass, yielding fibre for paper, rope etc.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: ‘Uromycesdactylidis. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960, and studied by us.

Special comments. An isolated genus of uncertain taxonomic affinities, despite good descriptive data. Primitive numerical taxonomic analyses of Metcalfe’s leaf blade anatomical descriptions conducted in 1963 (Watson, unpublished) presented Lygeum with Nardus as an ‘outlying’ group, and this has been a consistent feature of most analyses performed subsequently in course of developing this data set. They seem closest to Stipeae, but are prime candidates for comparative DNA studies. Illustrations. • L. spartum (as ‘sparteum’): P. Beauv. (1812). • L. spartum: Loefling and C. Linnaeus (1758), Inter Hispanicum t.2. • L. spartum, abaxial epidermis of leaf blade: 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.’.