| # The grass genera of the world |

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

### Nassella Desv.

Needle Grasses, Serrated Tussock.

~ Stipa p.p.

Type species: Lecto: N. pungens Desv.

Including Amelichloa, Anatherostipa p.p.

Habit, vegetative morphology. Perennial; caespitose. Culms 25–130 cm high; herbaceous; sparsely to amply branched above, or unbranched above (usually). The branching simple. Culm nodes hairy, or glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves mostly basal, or not basally aggregated. Leaf blades linear; narrow; 1–4(–5) mm wide; setaceous (sometimes filiform), or not setaceous; flat, or folded, or rolled (convolute or involute), or acicular; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate. Contra-ligule absent (?).

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence paniculate; deciduous in its entirety, or not deciduous; open, or contracted; with capillary branchlets (at least sometimes), or without capillary branchlets (?); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets (1–)2–22 mm long; compressed laterally, or not noticeably compressed; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. The callus hairs brown. Callus short to long (0.5–4 mm long); pointed, or blunt.

Glumes two; very unequal to more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (exceeding them); hairless; pointed; awned to awnless (long-acuminate); non-carinate (rounded on the back); similar (tapering from near the base, often anthocyanic). Lower glume 3 nerved (?). Upper glume 3 nerved (?). Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas tightly convolute (the margins much overlapped, concealing the palea); saccate (above, the gibbous floret characteristic of Nassella sensu stricto), or not saccate (the floret being symmetrical in most species of Nassella sensu lato); with an apical ‘crown’ (with or without a corona of hairs, and less conspicuous in the species with reduced awns and gibbous florets); decidedly firmer than the glumes; papillose or tuberculate, at least above; becoming indurated; entire to incised (depending on degree of fusion of the lobes, and interpretation of the ‘crown’); not deeply cleft; awned. Awns 1; median (or borne asymmetrically); from a sinus, or apical (depending on interpretation of the ‘crown’); geniculate; hairless (scabrid), or hairy; about as long as the body of the lemma (?), or much longer than the body of the lemma (mostly, commonly 11 cm or more long); entered by several veins; deciduous (in gibbous-floreted Nassella sensu stricto), or persistent. Lemmas hairy, or hairless; when ‘hairless’, glabrous, or scabrous (or tuberculate); non-carinate; having the margins lying flat on the palea (but very convolute); without a germination flap; obscurely 3 nerved (?); with the nerves confluent towards the tip. Palea present; conspicuous but relatively short to very reduced (consistently less than a third of the lemma length); not prow-tipped; entire; awnless, without apical setae; thinner than the lemma (scarious); not indurated; consistently nerveless; keel-less. Palea back glabrous. Lodicules present; 2 (in material of N. trichotoma seen); membranous (‘stipoid’); glabrous; not toothed; not or scarcely vascularized. Stamens 1–3. Anthers penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit small to medium sized (?); ovate or oblong to pyriform; not grooved; compressed laterally, or not noticeably compressed. Hilum long-linear. Embryo large to small; waisted, or not waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast (the epiblast very long to short, notched or not); without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

First seedling leaf with a well-developed lamina. The lamina narrow; curved.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (e.g. N. hyalina, N. filiculmis, N. leucotricha), or lacking (at least, fairly inconspicuous in N. trichotoma). Papillae absent. Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the costals usually smaller); of similar wall thickness costally and intercostally (e.g. all thick-walled and pitted in N. trichotoma), or differing markedly in wall thickness costally and intercostally (very to fairly thin walled with the costals somewhat thicker, in N. hyalina, N. filiculmis, N. leucotricha). Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls (in N. hyalina, and fairly straight in N. leucotricha). Microhairs absent. Stomata common (in N. hyalina), or absent or very rare (scarce in N. trichotoma, none seen in the other species); in N. trichotoma 28.5–30 microns long. Subsidiaries non-papillate; low to high dome-shaped. Intercostal short-cells common; mostly in cork/silica-cell pairs; silicified, or silicified to not silicified (N. leucotricha). Intercostal silica bodies absent to imperfectly developed (N. leucotricha), or present and perfectly developed; rounded, or crescentic (often, somewhat), or tall-and-narrow (and very irregular in N. leucotricha). Numerous large, thick walled, mainly costal prickles in N. filiculmis and N. trichotoma, none seen in N. leucotricha. Costal short-cells conspicuously in long rows (mostly, but pairs also common in N. hyalina). Costal silica bodies present and well developed; present throughout the costal zones; ‘panicoid-type’, or tall-and-narrow, or horizontally-elongated smooth to rounded (panicoid forms conspicuous in all four species examined, the other forms and cuboids also recorded in N. hyalina); mostly cross shaped (N. hyalina), or dumb-bell shaped (mostly, short, in N. filiculmis and N. trichotoma), or dumb-bell shaped and nodular (especially in N. leucotricha).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (N. filiculmis, N. trichotoma), or with the ribs very irregular in sizes (N. leucotricha). Midrib not readily distinguishable (except positionally); 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 (only N. filiculmis); in simple fans (in Ammophila-type groups of small cells, or strong to weak fans, in the bases of the furrows). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with most bundles); forming ‘figures’ (I’s and/or ‘anchors’). Sclerenchyma all associated with vascular bundles (N. hyalina, N. leucotricha), or not all bundle-associated (N. filiculmis, N. trichotoma). The ‘extra’ sclerenchyma when present, in abaxial groups (represented in N. filiculmis by occasional cells detached from the ‘feet’ of the ‘anchors’), or in a continuous abaxial layer (in N. trichotoma); abaxial-hypodermal, the groups isolated.

Phytochemistry. Tissues of the culm bases with abundant starch.

Special diagnostic feature. Spikelet with a single gibbous floret, the lemma awn placed off-centre (Nassella sensu stricto), or spikelet not as in Nassella (q.v.) (mostly).

Cytology. 2n = 38 (N. trichotoma).

Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. About 80 species.

Distribution, phytogeography, ecology. North and (mainly) South America.

Commonly adventive. Mesophytic to xerophytic; species of open habitats; glycophytic.

Economic aspects. Significant weed species: N. trichotoma (in pastures).

Hybrids. Hybrids between N. viridula and Achnatherum hymenoides - ×Stiporyzopsis B.L. Johnson & Rogler, ×Achnella Barkworth.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminella.

References, etc. Morphological/taxonomic: Barkworth 1990. Leaf anatomical: Metcalfe 1960, 2 species; studied by us - N. pubiflora (Trin. & Rupr.) Desv., N. trichotoma (Nees) Hackel ex Arechav.

Special comments. This description is an attempt to portray Nassella sensu lato (cf. Barkworth 1990), which takes in numerous South American species formerly assigned to Stipa.

Illustrations. • Nassella trichotoma, as Stipa: Kunth (1835). • General aspect (Nassella trichotoma): Gibbs Russell et al., 1990. • Nassella trichotoma, abaxial epidermis of leaf blade: this project. • Nassella trichotoma, TS part of leaf blade: this project. • Nassella trichotoma, entire leaf blade transverse section: 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: 15th June 2025. delta-intkey.com’.

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