Brachyachne (Benth.) Stapf
From the Greek brachys (short) and achne (scale, chaff), alluding to lemmas shorter than glumes.
Excluding Lepturidium
Habit, vegetative morphology. Annual, or perennial; stoloniferous, or caespitose. Culms 870 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves non-auriculate. Leaf blades linear; narrow; setaceous, or not setaceous; flat, or rolled (involute and filiform); without abaxial multicellular glands; without cross venation; persistent; a fringed membrane to a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence usually of spicate main branches (occasionally the racemes single); digitate. Rachides hollowed, or flattened (or triquetrous). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary (appressed); secund (the racemes unilateral); biseriate; subsessile.
Female-fertile spikelets. Spikelets adaxial; strongly compressed laterally; disarticulating above the glumes. Rachilla usually prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets, or naked. Hairy callus present. Callus short; pointed, or blunt.
Glumes two; more or less equal; exceeding the spikelets (enclosing the floret); long relative to the adjacent lemmas; lateral to the rachis; pointed, or not pointed (sometimes minutely incised, with a tiny mucro); awnless; (at least the lower) carinate (the keel weak to very strong); with the keel conspicuously winged (especially the lower, in B. convergens), or without a median keel-wing; very dissimilar (broad, usually thinly leathery, the lower curved in profile, the upper straighter). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped (tiny). Spikelets without proximal incomplete florets.
Female-fertile florets 1. Lemmas less firm than the glumes to similar in texture to the glumes (membranous to hyaline); not becoming indurated; entire, or incised; when entire, pointed, or blunt; when incised, 2 lobed; not deeply cleft; awnless, or mucronate (rarely); hairy (long-haired on the nerves or all over); carinate (folded along the mid-nerve); 3 nerved. Palea present; relatively long to conspicuous but relatively short; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (with long hairs). Lodicules present; 2; joined, or free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; not waisted. Endosperm containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata; consisting of one symmetrical projection per cell. Long-cells the intercostals broader, often short; of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells, or exhibiting many atypical long-cells. Mid-intercostal long-cells rectangular (to square); having markedly sinuous walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 6 microns long. Stomata common. Subsidiaries non-papillate. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (mainly solitary); silicified (mostly), or not silicified (usually). Intercostal silica bodies imperfectly developed; tall-and-narrow (rare). Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines uneven, or even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral, or centripetal. Mesophyll with radiate chlorenchyma. Leaf blade nodular in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles.
Taxonomy. Chloridoideae; main chloridoid assemblage. Native Couch.
Distribution, ecology, phytogeography. 10 species; Africa, Australia. Helophytic to mesophytic; species of open habitats; glycophytic. Seasonal swamps and moist rock crevices.
Paleotropical and Australian. African and Indomalesian. Sudano-Angolan and West African Rainforest. Malesian and Papuan. North and East Australian and Central Australian. Sahelo-Sudanian, Somalo-Ethiopian, and South Tropical African. Tropical North and East Australian.
Economic importance. Significant weed species: B. convergens (in North America).
References, etc. Leaf anatomical: this project.
Illustrations. General aspect. General aspect. Spikelet. Brachyachne convergens.
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).