Acamptoclados Nash
Sometimes referred to 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; a fringe of hairs (the adjoining blade also hairy). Contra-ligule present (partial, of small hairs).
Reproductive organization. Plants bisexual, 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.
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 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.
Taxonomy. Chloridoideae; main chloridoid assemblage.
Distribution, ecology, phytogeography. 1 species; North America to Mexico. Mesophytic to xerophytic; species of open habitats. Plains and sandy prairies.
Holarctic. Boreal. Atlantic North American. Southern Atlantic North American.
References, etc. Leaf anatomical: this project.
Illustrations. • Abaxial epidermis of leaf blade. Acamptoclados sessilispica.
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
