The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms 40–200 cm high; herbaceous; unbranched above. Young shoots intravaginal. Leaves mostly basal; non-auriculate. The sheath bases woolly-tomentose. Leaf blades broad (up to 2 cm in A. oreogena), or narrow; flat, or rolled; without cross venation; disarticulating from the sheaths. Ligule a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; narrow; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 6–26 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets (above the persistent first floret). Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus present. Callus short; blunt.
Glumes two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairy (pilose), or hairless; sometimes glabrous; pointed (acute, acuminate or minutely bidentate); more or less awned (mucronate to aristate, apically or from between short teeth); carinate; very dissimilar (with entire G1 and bidentate G2), or similar. Lower glume 3 nerved, or 5 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with incomplete florets. The incomplete florets both distal and proximal to the female-fertile florets (usually). The distal incomplete florets merely underdeveloped. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; male (usually - though in three species the L1 is occasionally hermaphrodite). The proximal lemmas awned (from a slight or deep sinus, the awn short and straight to long and geniculate); 5 nerved; exceeded by the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (thinly membranous to papery); not becoming indurated.
Female-fertile florets 5–10. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated; incised; 2 lobed; deeply cleft, or not deeply cleft (but always strongly bidentate); awned. Awns 1, or 3; median, or median and lateral (the lobes being aristate); the median different in form from the laterals (when laterals present); from a sinus; geniculate; hairless; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas usually hairy. The hairs in tufts (one on each side); not in transverse rows. Lemmas non-carinate (dorsally rounded); 5 nerved. Palea present; relatively long; entire to apically notched; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled. Stamens 3. Anthers 1–6.4 mm long. Stigmas 2.
Ovule, embryology. Synergids not haustorial.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (intercostals much broader); of similar wall thickness costally and intercostally (rather thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present (but scarce in material seen); panicoid-type (probably, but apical cells not seen); 36–45 microns long; 6–7 microns wide at the septum. Microhair total length/width at septum 5–6.5. Microhair apical cells 6–9 microns long. Microhair apical cell/total length ratio 0.15–0.2. Stomata common (but not abundant); 33–39 microns long. Subsidiaries low dome-shaped. Guard-cells overlapped by the interstomatals (sometimes; slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows (but the short-cells often quite long). Costal silica bodies panicoid-type; predominantly elongated dumb-bell shaped.
Transverse section of leaf blade, physiology. C3 (indisputably); XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes (small round-topped, alternating with large flat-topped). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (in the furrows). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); forming figures (the primaries with massive Is). Sclerenchyma not all bundle-associated (with a small abaxial group opposite each furrow). The extra sclerenchyma in abaxial groups; abaxial-hypodermal, the groups isolated.
Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae. 6 species.
Distribution, phytogeography, ecology. Angola, Tanzania, Malawi.
Xerophytic; species of open habitats.
References, etc. Morphological/taxonomic: Kabuye and Renvoize 1975. Leaf anatomical: studied by us - A. geniculata (Rendle) C.E. Hubb.
Special comments. 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: 11th December 2017. delta-intkey.com/grass’.