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The grass genera of the world

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

Achlaena Griseb.

~ Arthropogon

Type species: A. piptostachya (Grisb) Pilg.).

Habit, vegetative morphology. Perennial; caespitose. Culms 50–100 cm high; herbaceous. Culm nodes glabrous. Leaves mostly basal; non-auriculate. Leaf blades linear-lanceolate; narrow; 2–6 mm wide; flat, or rolled (involute); not pseudopetiolate; without cross venation; persistent. Ligule a fringed membrane; 0.5–1 mm long.

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

Inflorescence. Inflorescence paniculate; open (long exserted, 7–15 cm long, the branches somewhat glutinous); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; pedicellate.

Female-fertile spikelets. Spikelets 6–8 mm long; compressed laterally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present (stipitate, minutely barbed). Callus pointed.

Glumes narrow, two; relatively large; very unequal (G1 shorter); (the longer) long relative to the adjacent lemmas; without conspicuous tufts or rows of hairs; pointed; awned (G1 extending into, G2 narrowed into slender, antrorse-scabrid awns); very dissimilar (G1 subulate, G2 broader, somewhat hardened). Lower glume 1 nerved. Upper glume 5 nerved, or 7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 5 nerved, or 7 nerved; more or less equalling the female-fertile lemmas; decidedly firmer than the female-fertile lemmas (rather hard).

Female-fertile florets 1. Lemmas less firm than the glumes; not becoming indurated (thin, hyaline); entire; pointed; awnless (but acuminate); without a germination flap; 1 nerved, or 3 nerved. Palea present; relatively long to conspicuous but relatively short; awnless, without apical setae; thinner than the lemma (hyaline); not indurated; 2-nerved. Lodicules present; 2; free. Stamens 2.

Fruit, embryo and seedling. Hilum short (oval). Embryo small (about 1/4 of the grain length).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated (plump); clearly two-celled; panicoid-type; 72–81 microns long; 18–21 microns wide at the septum. Microhair total length/width at septum 3.5–4.3. Microhair apical cells 43.5–49.5 microns long. Microhair apical cell/total length ratio 0.56–0.63. Stomata common; 48–52.5 microns long. Subsidiaries triangular (predominating), or dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (in places), or not paired. Costal short-cells predominantly paired. Costal silica bodies oryzoid to ‘panicoid-type’; when panicoid type, cross shaped (i.e. silica bodies vertical dumb-bell shaped to cross shaped).

Transverse section of leaf blade, physiology. C4. The anatomical organization unconventional. Organization of PCR tissue Arundinella type (with extra PCR cells as lateral extensions from the sheaths of small bundles, as isolated clusters, and solitary). XyMS+. PCR sheath extensions absent. Mesophyll without adaxial palisade; exhibiting ‘circular cells’. Leaf blade slightly ‘nodular’ in section; with the ribs more or less constant in size (low, flat to roundish-topped). Midrib conspicuous; having a conventional arc of bundles (with numerous major and minor bundles); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (most of the main bundles with large I’s). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae (Arthropogoneae). Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Arthropogoninae. 1 species (A. piptostachya).

Distribution, phytogeography, ecology. Cuba and Jamaica.

Species of open habitats. Open woods, dry slopes, savanna.

References, etc. Morphological/taxonomic: e.g. Filgueiras 1982. Leaf anatomical: studied by us.

Special comments. Evidently close to Arthropogon, but seems fairly distinct morphologically and anatomically, as well as geographically. Fruit data wanting. Illustrations. • A. piptostachya: Hitchcock , W.I. Grasses (1936).

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: 11th December 2017.’.