| # The grass genera of the world |

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

### Nastus Juss.

Including Chloothamnus Büse, Oreiostachys Gamble, Stemmatospermum P. Beauv.

Habit, vegetative morphology. Arboresent or scrambling perennial. Culms woody and persistent; to 2–26 cm in diameter; scandent; branched above. Primary branches 3 (N. longispicula), or 4–20 (usually ‘many’). The branching dendroid. Culm leaf sheaths present. Culm leaves where recorded, with conspicuous blades. Culm leaf blades lanceolate, or ovate, or triangular. Rhizomes pachymorph. Plants unarmed. Leaf blades broad, or narrow; 3–30 mm wide; pseudopetiolate; disarticulating from the sheaths; rolled in bud. Ligule an unfringed membrane to a fringe of hairs. Contra-ligule consistently absent.

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

Inflorescence. Inflorescence without pseudospikelets (the ‘glumes’ all barren); reduced to a single spikelet, or few spikeleted, or many spikeleted; a single raceme, or paniculate (terminating leafy branches); spatheate (the panicles bracteate), or espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’, or paniculate; persistent. Spikelets not secund; subsessile, or pedicellate; consistently in ‘long-and-short’ combinations, or not in distinct ‘long-and-short’ combinations. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite.

Female-fertile spikelets. Spikelets 8.5–25 mm long; oblong, or lanceolate, or ovate; compressed laterally; disarticulating between the glumes (2–3 of them deciduous with the floret). Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret; the rachilla extension when present, with incomplete florets (with a rudiment).

Glumes present; several (4–6 ‘barren glumes’); increasing in size acropetally; shorter than the adjacent lemmas; hairy, or hairless; often apiculate, the lower sometimes with setiform tips. Lower glume 9–13 nerved (in material seen). Upper glume 9–13 nerved (in material seen). Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets 1. Lemmas similar in texture to the glumes (firmly membranous); entire; pointed; awnless, or mucronate (?); hairy, or hairless; 11–15 nerved (in material seen). Palea present; relatively long; not convolute; apically notched; awnless, without apical setae; several nerved (13–17 in material seen); 2-keeled, or keel-less (when rachilla extension present). Lodicules present; 3 (very large); free; membranous; ciliate; heavily vascularized. Stamens 6. Anthers not penicillate; without an apically prolonged connective. Ovary apically hairy; with a conspicuous apical appendage (commonly), or without a conspicuous apical appendage. The appendage broadly conical, fleshy (expanded, fleshy, sometimes hollow, but not attenuated into the style). Styles fused. Stigmas 3.

Fruit, embryo and seedling. Pericarp fleshy.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata (which are sunken); several per cell (mostly large, around the stomata). Long-cells markedly different in shape costally and intercostally (the costals longer); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (thin). Microhairs present; panicoid-type; (54–)57–78(–81) microns long; 8.4–9.6 microns wide at the septum. Microhair total length/width at septum 6–9. Microhair apical cells (24–)25.5–39(–40.5) microns long. Microhair apical cell/total length ratio 0.43–0.56. Stomata common (obscured by papillae); 24–30(–34.5) microns long. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or saddle shaped. With large short-pointed, bulbous intercostal prickles, their bases ringed by pits in the adjoining cells. Crown cells absent. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (but often paired). Costal silica bodies saddle shaped, tall-and-narrow, crescentic, and oryzoid (predominantly saddles, sometimes merging into the others); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+ (the MS sometimes double). Mesophyll with adaxial palisade; with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only (large, embedded in lignified tissue), or having complex vascularization. Bulliforms present in discrete, regular adaxial groups (these very large, in every intercostal zone); in simple fans, or in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with most bundles); forming ‘figures’ (in many bundles). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Hickeliinae. 7 species.

Distribution, phytogeography, ecology. Malesia, New Guinea.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - N. obtusus Holttum.

Special comments. Fruit data wanting.

Illustrations. • Nastus borbonicus, as Stemmatospermum verticillatum: P. Beauv. (1812). • Nastus elegantissimus (as Oreiostachys), with Bonia and Fargesia: Camus (1913). • Camus legend. • Nastus hooglandii, leaf blade TS: this project. • Nastus obtusus, 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: 15th June 2025. delta-intkey.com’.

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