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The grass genera of the world

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

Apocopis Nees

Including Amblyachyrum Steud.

Habit, vegetative morphology. Annual, or perennial (low, delicate). Culms herbaceous; branched above, or unbranched above. Leaf blades narrow; not pseudopetiolate; without cross venation. Ligule an unfringed membrane (ciliolate).

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets (rarely), or without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, or hermaphrodite and sterile (when the pedicelled spikelet detectable); overtly heteromorphic (the pedicelled members much reduced or absent, the lowermost spikelets awnless); all in heterogamous combinations.

Inflorescence. Inflorescence of solitary ‘racemes’, or these 2–3(-4)nate but closely appressed, terminal, exserted; digitate, or non-digitate (when the ‘racemes’ solitary). Primary inflorescence branches 1–3(–4). Inflorescence spatheate, or espatheate; a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikes, or ‘racemes’; solitary, or paired, or clustered; with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ without a basal callus-knob; not appendaged; disarticulating obliquely; somewhat hairy (bearded at the apex, ciliate on the margins). Spikelets paired (or the pedicellate members suppressed); sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets sterile (usually reduced to the pedicel, which is basally adnate to the lower glume of the sessile spikelet).

Female-fertile spikelets. Spikelets slightly compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus blunt.

Glumes two (often dark coloured); very unequal (G2 much smaller); long relative to the adjacent lemmas (the lower only, the upper being much smaller); not pointed (truncate); awnless (G2 sometimes with nerves excurrent as mucros); non-carinate; very dissimilar (G2 2–3 keeled, G1 flattened on the back and broadened above). Lower glume not two-keeled; convex on the back; not pitted; relatively smooth; obscurely 7–9 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; male. The proximal lemmas awnless; 0 nerved, or 1 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas linear; less firm than the glumes; incised; not deeply cleft (notched); mucronate (from the sinus), or awned. Awns 1; median; from a sinus (or mucronate); geniculate; hairy (puberulous); much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; non-carinate; without a germination flap; 1 nerved. Palea present; conspicuous but relatively short; convolute around the flower; entire (truncate or obtuse); awnless, without apical setae; not indurated (hyaline, glabrous); nerveless. Lodicules absent. Stamens 2. Anthers 0.75–3.5 mm long. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (large, scabrid). Intercostal papillae over-arching the stomata (laterally); consisting of one oblique swelling per cell to consisting of one symmetrical projection per cell. Long-cells of similar wall thickness costally and intercostally. Intercostal zones exhibiting many atypical long-cells (many being short and broad). Mid-intercostal long-cells intercostal long cells mostly hexagonal, many nearly isodiametric; having straight or only gently undulating walls. Microhairs present; panicoid-type; 30–45 microns long; 5.1–8.1 microns wide at the septum. Microhair total length/width at septum 3.2–8.3. Microhair apical cells 15–31.5 microns long. Microhair apical cell/total length ratio 0.48–0.75. Stomata common; 18–36 microns long. Subsidiaries variously dome-shaped (but the domes often more or less flat-topped), or triangular (in A. mangalorensis). Guard-cells overlapped by the interstomatals (slightly so, where not obscured by papillae). Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows (but many pairs and short rows over midrib). Costal silica bodies horizontally-elongated crenate/sinuous (a few, over the midrib), or ‘panicoid-type’ (imperfect forms, especially over the midrib), or acutely-angled (in the form of numerous, sharp-pointed crosses over all veins but the midrib); often sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous (by virtue of its slight abaxial expansion, and adaxial colourless tissue); with one bundle only to having a conventional arc of bundles (depending on interpretation); with colourless mesophyll adaxially (small group, over midrib). Bulliforms not present in discrete, regular adaxial groups (the adaxial epidermis mainly bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. 2n = 20 and 40.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Germainiinae. 15 species.

Distribution, phytogeography, ecology. Burma, India, China and Southeast Asia.

Xerophytic; species of open habitats. In dry shallow soils.

References, etc. Leaf anatomical: studied by us - A. courtallumensis (Steud.) Henr., A. mangalorensis (Hochst.) Henr.

Illustrations. • A. wightii: Rangachariyar Kadambi (1921), Hndbk. of S. Indian Grasses. • A. wightii: Rangachariyar Kadambi (1921), Hndbk. of S. Indian Grasses

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.’.