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The grass genera of the world

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

Piptatherum P. Beauv.

~ Oryzopsis

Type species: Type: P. coerulescens (Desf.) P.Beauv.

Including Urachne Trin., Oloptum, Piptatheropsis p.p.

Habit, vegetative morphology. Perennial; densely or loosely caespitose. Culms 10–140 cm high; herbaceous; at least sometimes unbranched above. Culm nodes glabrous. Culm internodes solid, or hollow (?). Young shoots extravaginal, or intravaginal. Leaves non-auriculate. Leaf blades broad to narrow; 0.7–15 mm wide; not setaceous; flat, or folded, or rolled (involute); not pseudopetiolate; without cross venation; persistent; rolled in bud, or once-folded in bud (?). Ligule an unfringed membrane; truncate to not truncate; 0.2–15 mm long.

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

Inflorescence. Inflorescence paniculate; open (usually with 1–3(-5) branches at the lower nodes); with capillary branchlets, or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 2–9 mm long; compressed dorsiventrally (dorsally compressed to subterete); disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus short (0.1–0.3 mm long, mostly incurved); blunt (glabrous).

Glumes present; two; more or less equal (subequal); about equalling the spikelets, or exceeding the spikelets; long relative to the adjacent lemmas; generally with small asperities, at least above; pointed; awnless; non-carinate; similar. Lower glume 3–5 nerved (-7). Upper glume 3–7 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas not convolute (the palea back exposed); not saccate; with an apical ‘crown’; decidedly firmer than the glumes; becoming indurated; brown in fruit, or black in fruit (usually dark brown to black and shiny, brown in P. miliaceum); inconspicuously incised, or entire; sometimes obscurely 2 lobed; not deeply cleft; awned. Awns 1 (fine); median (to excentric?); from a sinus, or apical (when lemma lobes absent); non-geniculate; usually straight (erect, neither twisted nor curved); hairless (scabrous); much shorter than the body of the lemma to much longer than the body of the lemma; deciduous (except in P. virescens). Lemmas hairy (the hairs white or golden to brown), or hairless; non-carinate; having the margins inrolled against the palea; 3–5 nerved (rarely more?). Palea present (only the margins covered by the lemma); relatively long (equalling the lemma); prow-tipped; awnless, without apical setae; textured like the lemma; not indurated (leathery); 2-nerved; keel-less. Palea back glabrous to hairy (usually hairy?). Lodicules present; 3. Third lodicule present. Lodicules free; membranous (two ‘stipoid’ and two-nerved, one thinner and nerveless); glabrous; not toothed; heavily vascularized (the stipoid pair), or not or scarcely vascularized (the third). Stamens 3. Anthers 1.5–4.5 mm long; penicillate (usually), or not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small to medium sized (1.5–4.0 mm long); compressed dorsiventrally. Hilum long-linear. Embryo large to small (usually about a third of the grain length). Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast (the epiblast short, truncate); without a scutellar tail (with a 95–130 degree angle between coleoptile and coleorhiza); with a negligible mesocotyl internode. Embryonic leaf margins meeting (unreliably - these embryo data, from Reeder, may refer to Oryzopsis).

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

Ovule, embryology. Micropyle oblique. Outer integument extensive, being absent only from the micropylar region; two cells thick at the micropylar margin. Inner integument continuous, the micropyle constricted; thickened around the micropyle. Synergids not haustorial (‘Oryzopsis micrantha’); without large, globular starch grains.

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 (fairly thin to fairly thick (P. miliaceum) walled, the costals somewhat thicker). Mid-intercostal long-cells rectangular; having markedly sinuous walls (and heavily pitted, in P. miliaceum), or having markedly sinuous walls to having straight or only gently undulating walls. Microhairs absent (but the stipoid type, q.v., sometimes occur adaxially). Stomata common (e.g. P. paradoxum), or absent or very rare (e.g. P. racemosum); 21–34 microns long. Subsidiaries non-papillate; low to high dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or in cork/silica-cell pairs and not paired (some solitary); silicified (in the pairs). Intercostal silica bodies absent; rounded, or rounded to crescentic, or tall-and-narrow. Macrohairs not seen in either P. paradoxum or P. racemosum. Costal short-cells conspicuously in long rows (mostly, with a few pairs), or neither distinctly grouped into long rows nor predominantly paired (P. miliaceum). Costal silica bodies ‘panicoid-type’ (predominating in the rows of costal short-cells of both P. paradoxum and P. racemosum), or rounded, tall-and-narrow, and crescentic; when panicoid type, cross shaped, or dumb-bell shaped, or cross shaped to dumb-bell shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll slightly with radiate chlorenchyma, or with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs (e.g. P. miliaceum), or ‘nodular’ in section (P. racemosum); with the ribs more or less constant in size (e.g. P. paradoxum), or with the ribs very irregular in sizes (e.g. P. racemosum). Midrib conspicuous (via the sclerenchyma mass), or not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma (P. paradoxum), or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with most larger bundles); forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings.

Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid. Chromosomes ‘medium sized’.

Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. 25 species, or 26 species.

Distribution, phytogeography, ecology. Old World subtropics, North America.

Commonly adventive. Mesophytic to xerophytic.

Economic aspects. Significant weed species: P. miliaceum. Cultivated fodder: P. miliaceum.

Hybrids. Hybridizes with Achnatherum hymenoides (Stipa sensu lato).

References, etc. Morphological/taxonomic: Freitag 1975. Leaf anatomical: Metcalfe 1960; this project; Devesa 1992.

Special comments. Including the North American species usually known as Oryzopsis micranthum and O. racemosa in Piptatherum (cf. Barkworth 1993) permits this genus to be distinguished morphologically from Oryzopsis sensu stricto, while disavowing Freitag’s geographical distinction. Illustrations. • P. coerulescens: P. Beauv. (1812). • P. miliaceum: Gardner, 1952


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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’.

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