Aciachne Benth.
Habit, vegetative morphology. Perennial; cushion-forming and caespitose. Culms 1–2 cm high; herbaceous; unbranched above. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae. Sheath margins free. The sheaths overlapping, whitish, shining. Leaf blades linear; narrow; 0.3–0.8 mm wide; setaceous (recurved); acicular (and involute, pungent); without cross venation; persistent; an unfringed membrane; 1–1.5 mm long.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (the reduced inflorescence often exhibiting vestigial spikelets). Plants exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence reduced to a single spikelet, or few spikeleted; greatly reduced, barely extruded from the sheaths at anthesis; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets about 3 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes present; two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; not pointed (obtuse); awnless; non-carinate (rounded on the back); similar. Lower glume 3 nerved, or 5 nerved. Upper glume 5 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas fusiform; convolute; without a crown; similar in texture to the glumes (hard); becoming indurated (shiny); entire; pointed; awned. Awns 1; median; apical (the lemma extending into the sharp, firm point); non-geniculate; hairless; much shorter than the body of the lemma to about as long as the body of the lemma; persistent (with no line of demarcation from the body of the lemma). Lemmas hairless; non-carinate (abaxially rounded); having the margins lying flat on the palea; 3 nerved. Palea present; relatively long; tightly clasped by the lemma; not prow-tipped; awnless, without apical setae; textured like the lemma; 2-nerved; keel-less. Lodicules present; 3. Third lodicule present. Lodicules free; membranous (stipoid); glabrous; not toothed; heavily vascularized (the anterior members with one strong vein). Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit small (1.3–1.6 mm long); ellipsoid; not noticeably compressed (terete). Hilum long-linear. Embryo small; not waisted. Endosperm hard; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode; with one scutellum bundle. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent (and also absent adaxially). Stomata absent or very rare. Intercostal short-cells common; in cork/silica-cell pairs. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies rounded, or ‘panicoid-type’.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; in simple fans (or these ill defined). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in a continuous abaxial layer.
Cytology. Chromosome base number, x = 11. 2n = 22. 2 ploid.
Taxonomy. Stipoideae; Stipeae.
Distribution, ecology, phytogeography. 3 species; high Andes, northern Argentina to Costa Rica. Xerophytic; species of open habitats; glycophytic. High altitude grassland.
Neotropical. Andean.
References, etc. Morphological/taxonomic: Macfarlane and Watson 1980; Laegaard 1987. Leaf anatomical: this project.
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).