The grass genera of the world
~ Achnatherum, Stipa
Type species: J. ichu Ruiz & Pav.
Habit, vegetative morphology. Perennial; caespitose. Culms 25–150 cm high; herbaceous; unbranched above ("simple"). Culm nodes glabrous. Culm leaves present. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; 0.2–2 mm wide; not setaceous; flat, or folded, or rolled (then involute); without cross venation; persistent; rolled in bud, or once-folded in bud (?). Ligule an unfringed membrane; truncate; 0.1–0.5 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality; hermaphrodite. Plants without hidden cleistogenes (?).
Inflorescence. Inflorescence many spikeleted; paniculate; not deciduous (?); contracted; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate (the pedicels flattened, scabrous in J. plumosa).
Female-fertile spikelets. Spikelets 6–10 mm long; ovate; compressed laterally, or not noticeably compressed; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. The callus hairs white. Callus long (1–1.5 mm); pointed.
Glumes two; very unequal to more or less equal; shorter than the spikelets, or about equalling the spikelets; shorter than the adjacent lemmas (usually), or long relative to the adjacent lemmas (rarely, about equal to slightly longer than the lemma); hairless; glabrous; pointed; awnless; carinate, or non-carinate (?); similar (lanceolate). Lower glume 0.7–0.9 times the length of the upper glume; shorter than the lowest lemma (usually), or about equalling the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas narrowly fusiform; not convolute (?); not saccate; without a crown; decidedly firmer than the glumes; smooth; becoming indurated to not becoming indurated (less firm than in most Stipeae); brown in fruit (light brown to pinkish in J. plumosa); awned. Awns 1; median; apical (?); geniculate (twice bent); hairless (scabrous, sometimes only minutely so); much longer than the body of the lemma (15–30 mm long in J. plumosa); persistent. Awn bases twisted. Lemmas hairy (the hairs long, restricted to the upper part of the lemma, characteristically pappus-like); non-carinate (terete); without a germination flap (?). Palea present; conspicuous but relatively short (e.g., only about 20% of the lemma length in J. plumosa); not convolute; tightly clasped by the lemma; awnless, without apical setae; thinner than the lemma; indurated, or not indurated (?); keel-less. Palea back glabrous. Stamens 3. Anthers 3.5 mm long.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small to medium sized (3–5 mm long); narrowly fusiform.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls and having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries non-papillate; dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (and also some short rows); silicified. Intercostal silica bodies present and perfectly developed; crescentic and cross-shaped (plus some imperfect panicoid forms). Costal silica bodies present and well developed; present throughout the costal zones; horizontally-elongated crenate/sinuous, horizontally-elongated smooth, rounded, and panicoid-type (with intermediates); including small, irregular dumb-bells and nodular forms, some of the latter almost crenate.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma (the chlorenchyma spongy); without adaxial palisade. Leaf blade nodular in section to adaxially flat. Midrib with one bundle only; without colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (accompanying all the bundles); forming figures. The lamina margins with fibres.
Special diagnostic feature. The upper part of the lemma exhibiting a conspicuous, pappus-like arrangement of long hairs.
Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. About 10 species (most of them not yet formally transferred from Stipa or Achnatherum).
Distribution, phytogeography, ecology. South and Central America, including Andes; ranging from Mexico to Argentina and Chile.
Not commonly adventive. Mesophytic to xerophytic; species of open habitats.
Economic aspects. J. ichu was, at least at one time, used for thatching in the Andes.
References, etc. Morphological/taxonomic: Description encoded by T.D. Macfarlane (1998) from Gardener, Jessop & Symon (1996) and Jacobs & Everett (1997). Leaf anatomical: this project: present description restricted to incomplete observations by L.W. on preparations from J. ichu.
Special comments. An as yet incomplete description of a Stipa segregate, previously Stipa subg. Jarava). Jarava includes S. ambigua, Stipa breviseta, Stipa eriostachya, S. gynerioides, S. ichu (= Achnatherum ichu), S. plumosa (= Stipa papposa, Achnatherum papposa), S. pseudoichu, S. pugionata, S. pungens, S. subaristata. The present morphological description is based mainly on J. plumosa (= Stipa papposa nom. illeg., Achnatherum papposum). Fruit data wanting.
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: 13th November 2017. delta-intkey.com/grass’.