| # The grass genera of the world |

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

### Acamptoclados Nash

~ Eragrostis (E. sessilispica Buckl.)

Habit, vegetative morphology. Perennial; caespitose. Culms (30–)40–50(–60) cm high (?); herbaceous; unbranched above; tuberous (when young); 1 noded (above the basal tuft of leaves). Culm nodes hidden by leaf sheaths. Plants unarmed. Young shoots extravaginal. Leaves mostly basal (the culm internodes very short); villous in the auricle positions. Glabrous, pilose at the throat. Leaf blades linear (narrowly so, stiff and subulate-tipped, almost acicular); narrow; 1–3 mm wide; flat, or rolled (flat to loosely involute); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs (the adjoining blade also hairy). Contra-ligule present (partial, of small hairs).

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

Inflorescence. Inflorescence paniculate (the long-internoded primary branches distant, stiffly spreading, mostly bearing basal secondary branches, the latter mostly short and sometimes reduced to a single spikelet, the spikelets appressed); deciduous in its entirety; open (the axis curving or loosely spiral, pilose in the axils). Rachides hollowed and flattened. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelets distant, solitary; not secund; subsessile.

Female-fertile spikelets. Spikelets (7–)8–10(–12) mm long; compressed laterally; disarticulating above the glumes; not disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous); the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; more or less equal; shorter than the adjacent lemmas; lateral to the rachis; hairless; glabrous; pointed; awnless; carinate; similar (firmly membranous to cartilaginous). Lower glume longer than half length of lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 5–8. Lemmas similar in texture to the glumes (firmly membranous to cartilaginous); becoming somewhat indurated; entire; pointed; awnless; hairless; glabrous; carinate (the lateral nerves also slightly raised); without a germination flap; 3 nerved. Palea present; relatively long (prominently bowed out below); apically notched; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea keels slightly winged (above). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers medium sized; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; apparently not white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (about 1.5 mm long); not noticeably compressed. Hilum short. Pericarp free, or loosely adherent (?). Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally (rather thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs (45–)46–54(–61.5) microns long. Microhair basal cells 24–30 microns long. Microhairs 7.5–10.5 microns wide at the septum. Microhair total length/width at septum 6.1–7.2. Microhair apical cells (21–)25.5–27(–30) microns long. Microhair apical cell/total length ratio 0.47–0.55. Stomata common; 30–33 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (bordering the veins); not paired (solitary); not silicified. Intercostal silica bodies absent. Prickles abundant costally. Crown cells absent (but costal prickles with round or rectangular pitted bases). Costal short-cells predominantly paired (but many solitary). Costal silica bodies present throughout the costal zones; rounded to saddle shaped (a few), or crescentic (predominating).

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes (large, tall, square- or round-topped, and infrequent small ones). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (the adaxial fibre groups being contiguous with bundle sheath extensions); forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 1 species (A. sessilispicus).

Distribution, phytogeography, ecology. North America to Mexico.

Mesophytic to xerophytic; species of open habitats. Plains and sandy prairies.

References, etc. Leaf anatomical: studied by us.

Illustrations. • Acamptoclados sessilispicus (as Eragrostis): Hitchcock and Chase (1950). • A. sessilispicus: Britton and Brown (1913). • Acamptoclados sessilispicus, abaxial epidermis of leaf blade: this project. R.S.B.S. Taxonomy Laboratory (Canberra) slide. Slides and full details now housed at the Western Australian Herbarium.

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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