Arthropogon Nees
From the Greek arthron (joint) and pogon (beard).
Excluding Achlaena
Habit, vegetative morphology. Perennial; caespitose. Culms 60–100 cm high; herbaceous; unbranched above. Culm nodes glabrous. Leaves mostly basal, or not basally aggregated. Leaf blades linear, or linear-lanceolate; narrow; 1–6(–10) mm wide; setaceous (A. filifolius), or not setaceous; without cross venation; a fringed membrane, or a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality; hermaphrodite, or female-only.
Inflorescence. Inflorescence paniculate; open; with capillary branchlets (A. filifolius), or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 3–11 mm long; compressed laterally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present (not stipitate, by contrast with Achlaena).
Glumes two; very unequal (G2 longer); awned (the G1 subulate); very dissimilar (the lower linear to awnlike, the upper equalling the spikelet, entire, bidentate or bilobed, awned). Lower glume 1 nerved, or 3 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate (e.g. A. scaber); male (e.g. A. filifolius), or sterile. The proximal lemmas awned (A. xerachne), or awnless; 3 nerved, or 5 nerved; decidedly exceeding the female-fertile lemmas; decidedly firmer than the female-fertile lemmas (leathery); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (membranous); not becoming indurated; awnless; without a germination flap; 0 nerved, or 1 nerved, or 3 nerved. Palea present, or absent; conspicuous but relatively short to very reduced; awnless, without apical setae; thinner than the lemma, or textured like the lemma (membranous or hyaline); not indurated (scarious); 2-nerved, or nerveless. Lodicules present; 2. Stamens 3. Ovary glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit deciduous with lemma and palea; small to medium sized; chestnut brown in A. villosus. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls (conspicuously pitted). Microhairs present; panicoid-type. Stomata common. Subsidiaries mostly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic. With large cushion-based macrohairs. Costal short-cells conspicuously in long rows (but the short-cells often rather long, or irregular in length). Costal silica bodies rounded and ‘panicoid-type’; shortly dumb-bell shaped, or nodular (and irregular forms, integrading with potato-shapes, etc.).
Transverse section of leaf blade, physiology. C4. The anatomical organization conventional, or unconventional. Organization of PCR tissue when unconventional, Arundinella type. XyMS+ (? - see photo of A. lanceolatus in Filgueiras 1982), or XyMS– (A. villosus). Mesophyll with radiate chlorenchyma; exhibiting ‘circular cells’, or without ‘circular cells’ (but with many small bundles much reduced in this direction). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (then epidermis seemingly extensively bulliform). All the vascular bundles accompanied by sclerenchyma (the small bundles and even some of the colourless groups with small abaxial strands). Combined sclerenchyma girders present; forming ‘figures’ (the primaries with I’s). Sclerenchyma all associated with vascular bundles.
Taxonomy. Panicoideae; Panicodae; Paniceae (Arthropogoneae).
Distribution, ecology, phytogeography. 5 species; Brazil. Species of open habitats. Savanna.
Neotropical. Caribbean and Central Brazilian.
Rusts and smuts. Rusts — Puccinia.
References, etc. Morphological/taxonomic: Filgueiras 1982. Leaf anatomical: this project for A. villosus; supplemented from photos in Filgueiras 1982.
Special comments. Most of the anatomical description refers to A. villosus, which has been examined directly. A photo of A. lanceolatus in Filgueiras (1982) suggests there is variation in XyMS.
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).