The grass genera of the world
Type species: Sitanion elymoides Raf., = Elymus elymoides (Raf.) Swezey?.
Habit, vegetative morphology. Perennial; caespitose. Culms 11–100 cm high; herbaceous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; auriculate. Leaf blades narrow; to 6 mm wide; flat, or folded, or rolled (convolute); without cross venation. Ligule an unfringed membrane; truncate; 0.3–1 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 (sterile spikelets accompanying the female-fertile ones, either irregularly in the clusters, or the central spikelet fertile and the laterals sterile).
Inflorescence. Inflorescence a single spike, or a false spike, with spikelets on contracted axes (with 1–4, but usually 2(-3), spikelets per node, very bristly via acicular glumes, awned lemmas and reduced spikelets); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; disarticulating at the joints. Spikelets associated with bractiform involucres (constituted by glumes), or unaccompanied by bractiform involucres, not associated with setiform vestigial branches; usually, fairly consistently paired; not secund; sessile.
Female-sterile spikelets. Sometimes with 1(-2)of the spikelets in each group sterile and reduced to groups of awns.
Female-fertile spikelets. Spikelets 5–15 mm long; not noticeably compressed; falling with the glumes (the pairs/clusters falling with the rachis segment); disarticulating between the florets (the rachilla often also fragile), or not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus absent.
Glumes two; relatively large; more or less equal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; displaced (borne side by side); awned (the awns scabrid, straight or flexuous); non-carinate; very dissimilar, or similar (cartilaginous basally, long, entire, bifid or deeply cleft into one to several awns). Lower glume 1–4 nerved. Upper glume 1–4 nerved. Spikelets usually with incomplete florets. The incomplete florets distal to the female-fertile florets (S. longifolium), or both distal and proximal to the female-fertile florets (usually, in at least one of the spikelets of a group). The distal incomplete florets 1; merely underdeveloped. The proximal incomplete florets when present, 1; epaleate; sterile. The proximal lemmas awned (reduced to an awn).
Female-fertile florets 1–6. Lemmas lanceolate; less firm than the glumes to similar in texture to the glumes; not becoming indurated (firm); incised; slightly 2 lobed; not deeply cleft (slightly bidentate); awned. Awns 1, or 3, or 5; median, or median and lateral (the lateral nerves sometimes excurrent as bristles); the median similar in form to the laterals (when laterals present); from a sinus, or apical; non-geniculate; much longer than the body of the lemma; entered by several veins. Lemmas hairy, or hairless; non-carinate; without a germination flap; 3–5 nerved. Palea present; relatively long; awnless, without apical setae, or awned; 2-nerved (these sometimes extending into awns to 5 mm long); 2-keeled. Lodicules present; 2; free; membranous; ciliate, or glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Anthers 1–2 mm long. Ovary apically hairy. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit adhering to lemma and/or palea; medium sized (5–6 mm long); longitudinally grooved; compressed dorsiventrally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo small. Endosperm hard; without lipid. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (the costals somewhat narrower); of similar wall thickness costally and intercostally (rather thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (conspicuously pitted). Microhairs absent. Stomata common; (33–)34–36 microns long. Subsidiaries low dome-shaped (exclusively). Guard-cells overlapped by the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Short prickles common. Crown cells absent (but the prickles with crown-cell like bases). Costal short-cells neither distinctly grouped into long rows nor predominantly paired (solitary, paired and in short rows). Costal silica bodies tall-and-narrow, or crescentic; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the largest bundles); forming figures (conspicuous Is). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 28. 4 ploid. Haplomic genome content H and S.
Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 4 species.
Distribution, phytogeography, ecology. Western temperate North America.
Hybrids. Integeneric hybrids with Agropyron (×Agrositanion Bowden), Elymus, Hordeum (×Sitordeum Bowden), Lophopyrum. See also ×Elysitanion Bowden.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia striiformis, Puccinia montanensis, and Puccinia recondita. Smuts from Ustilaginaceae. Ustilaginaceae Ustilago.
References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: this project.
Special comments. Sitanion is probably best regarded as a nonsense genus, given that in recent times the 40+ associated species names (including the type species) have all been dismissed as synonyms of Elymus sensu lato, etc., or hybrids. Illustrations. • S. hystrix: Hitchcock and Chase (1950). • S. hystrix, 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: 13th November 2017. delta-intkey.com/grass’.